PostgreSQL

Support for the PostgreSQL database.

The following table summarizes current support levels for database release versions.

Supported PostgreSQL versions

Support type

Versions

Supported version

9.6+

Best effort

8+

DBAPI Support

The following dialect/DBAPI options are available. Please refer to individual DBAPI sections for connect information.

Sequences/SERIAL/IDENTITY

PostgreSQL supports sequences, and SQLAlchemy uses these as the default means of creating new primary key values for integer-based primary key columns. When creating tables, SQLAlchemy will issue the SERIAL datatype for integer-based primary key columns, which generates a sequence and server side default corresponding to the column.

To specify a specific named sequence to be used for primary key generation, use the Sequence() construct:

Table('sometable', metadata,
        Column('id', Integer, Sequence('some_id_seq'), primary_key=True)
    )

When SQLAlchemy issues a single INSERT statement, to fulfill the contract of having the “last insert identifier” available, a RETURNING clause is added to the INSERT statement which specifies the primary key columns should be returned after the statement completes. The RETURNING functionality only takes place if PostgreSQL 8.2 or later is in use. As a fallback approach, the sequence, whether specified explicitly or implicitly via SERIAL, is executed independently beforehand, the returned value to be used in the subsequent insert. Note that when an insert() construct is executed using “executemany” semantics, the “last inserted identifier” functionality does not apply; no RETURNING clause is emitted nor is the sequence pre-executed in this case.

To force the usage of RETURNING by default off, specify the flag implicit_returning=False to create_engine().

PostgreSQL 10 and above IDENTITY columns

PostgreSQL 10 and above have a new IDENTITY feature that supersedes the use of SERIAL. The Identity construct in a Column can be used to control its behavior:

from sqlalchemy import Table, Column, MetaData, Integer, Computed

metadata = MetaData()

data = Table(
    "data",
    metadata,
    Column(
        'id', Integer, Identity(start=42, cycle=True), primary_key=True
    ),
    Column('data', String)
)

The CREATE TABLE for the above Table object would be:

CREATE TABLE data (
    id INTEGER GENERATED BY DEFAULT AS IDENTITY (START WITH 42 CYCLE),
    data VARCHAR,
    PRIMARY KEY (id)
)

Changed in version 1.4: Added Identity construct in a Column to specify the option of an autoincrementing column.

Note

Previous versions of SQLAlchemy did not have built-in support for rendering of IDENTITY, and could use the following compilation hook to replace occurrences of SERIAL with IDENTITY:

from sqlalchemy.schema import CreateColumn
from sqlalchemy.ext.compiler import compiles


@compiles(CreateColumn, 'postgresql')
def use_identity(element, compiler, **kw):
    text = compiler.visit_create_column(element, **kw)
    text = text.replace(
        "SERIAL", "INT GENERATED BY DEFAULT AS IDENTITY"
     )
    return text

Using the above, a table such as:

t = Table(
    't', m,
    Column('id', Integer, primary_key=True),
    Column('data', String)
)

Will generate on the backing database as:

CREATE TABLE t (
    id INT GENERATED BY DEFAULT AS IDENTITY,
    data VARCHAR,
    PRIMARY KEY (id)
)

Server Side Cursors

Server-side cursor support is available for the psycopg2, asyncpg dialects and may also be available in others.

Server side cursors are enabled on a per-statement basis by using the Connection.execution_options.stream_results connection execution option:

with engine.connect() as conn:
    result = conn.execution_options(stream_results=True).execute(text("select * from table"))

Note that some kinds of SQL statements may not be supported with server side cursors; generally, only SQL statements that return rows should be used with this option.

Deprecated since version 1.4: The dialect-level server_side_cursors flag is deprecated and will be removed in a future release. Please use the Connection.stream_results execution option for unbuffered cursor support.

Transaction Isolation Level

Most SQLAlchemy dialects support setting of transaction isolation level using the create_engine.isolation_level parameter at the create_engine() level, and at the Connection level via the Connection.execution_options.isolation_level parameter.

For PostgreSQL dialects, this feature works either by making use of the DBAPI-specific features, such as psycopg2’s isolation level flags which will embed the isolation level setting inline with the "BEGIN" statement, or for DBAPIs with no direct support by emitting SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL <level> ahead of the "BEGIN" statement emitted by the DBAPI. For the special AUTOCOMMIT isolation level, DBAPI-specific techniques are used which is typically an .autocommit flag on the DBAPI connection object.

To set isolation level using create_engine():

engine = create_engine(
    "postgresql+pg8000://scott:tiger@localhost/test",
    isolation_level = "REPEATABLE READ"
)

To set using per-connection execution options:

with engine.connect() as conn:
    conn = conn.execution_options(
        isolation_level="REPEATABLE READ"
    )
    with conn.begin():
        # ... work with transaction

There are also more options for isolation level configurations, such as “sub-engine” objects linked to a main Engine which each apply different isolation level settings. See the discussion at Setting Transaction Isolation Levels including DBAPI Autocommit for background.

Valid values for isolation_level on most PostgreSQL dialects include:

  • READ COMMITTED

  • READ UNCOMMITTED

  • REPEATABLE READ

  • SERIALIZABLE

  • AUTOCOMMIT

Setting READ ONLY / DEFERRABLE

Most PostgreSQL dialects support setting the “READ ONLY” and “DEFERRABLE” characteristics of the transaction, which is in addition to the isolation level setting. These two attributes can be established either in conjunction with or independently of the isolation level by passing the postgresql_readonly and postgresql_deferrable flags with Connection.execution_options(). The example below illustrates passing the "SERIALIZABLE" isolation level at the same time as setting “READ ONLY” and “DEFERRABLE”:

with engine.connect() as conn:
    conn = conn.execution_options(
        isolation_level="SERIALIZABLE",
        postgresql_readonly=True,
        postgresql_deferrable=True
    )
    with conn.begin():
        #  ... work with transaction

Note that some DBAPIs such as asyncpg only support “readonly” with SERIALIZABLE isolation.

New in version 1.4: added support for the postgresql_readonly and postgresql_deferrable execution options.

Temporary Table / Resource Reset for Connection Pooling

The QueuePool connection pool implementation used by the SQLAlchemy Engine object includes reset on return behavior that will invoke the DBAPI .rollback() method when connections are returned to the pool. While this rollback will clear out the immediate state used by the previous transaction, it does not cover a wider range of session-level state, including temporary tables as well as other server state such as prepared statement handles and statement caches. The PostgreSQL database includes a variety of commands which may be used to reset this state, including DISCARD, RESET, DEALLOCATE, and UNLISTEN.

To install one or more of these commands as the means of performing reset-on-return, the PoolEvents.reset() event hook may be used, as demonstrated in the example below (requires SQLAlchemy 1.4.43 or greater). The implementation will end transactions in progress as well as discard temporary tables using the CLOSE, RESET and DISCARD commands; see the PostgreSQL documentation for background on what each of these statements do.

The create_engine.pool_reset_on_return parameter is set to None so that the custom scheme can replace the default behavior completely. The custom hook implementation calls .rollback() in any case, as it’s usually important that the DBAPI’s own tracking of commit/rollback will remain consistent with the state of the transaction:

from sqlalchemy import create_engine
from sqlalchemy import event

postgresql_engine = create_engine(
    "postgresql+pyscopg2://scott:tiger@hostname/dbname",

    # disable default reset-on-return scheme
    pool_reset_on_return=None,
)


@event.listens_for(postgresql_engine, "reset")
def _reset_postgresql(dbapi_connection, connection_record, reset_state):
    dbapi_connection.execute("CLOSE ALL")
    dbapi_connection.execute("RESET ALL")
    dbapi_connection.execute("DISCARD TEMP")

    # so that the DBAPI itself knows that the connection has been
    # reset
    dbapi_connection.rollback()

Changed in version 1.4.43: Ensured the PoolEvents.reset() event is invoked for all “reset” occurrences, so that it’s appropriate as a place for custom “reset” handlers. Previous schemes which use the PoolEvents.checkin() handler remain usable as well.

See also

Reset On Return - in the Connection Pooling documentation

Setting Alternate Search Paths on Connect

The PostgreSQL search_path variable refers to the list of schema names that will be implicitly referred towards when a particular table or other object is referenced in a SQL statement. As detailed in the next section Remote-Schema Table Introspection and PostgreSQL search_path, SQLAlchemy is generally organized around the concept of keeping this variable at its default value of public, however, in order to have it set to any arbitrary name or names when connections are used automatically, the “SET SESSION search_path” command may be invoked for all connections in a pool using the following event handler, as discussed at Setting a Default Schema for New Connections:

from sqlalchemy import event
from sqlalchemy import create_engine

engine = create_engine("postgresql+psycopg2://scott:tiger@host/dbname")

@event.listens_for(engine, "connect", insert=True)
def set_search_path(dbapi_connection, connection_record):
    existing_autocommit = dbapi_connection.autocommit
    dbapi_connection.autocommit = True
    cursor = dbapi_connection.cursor()
    cursor.execute("SET SESSION search_path='%s'" % schema_name)
    cursor.close()
    dbapi_connection.autocommit = existing_autocommit

The reason the recipe is complicated by use of the .autocommit DBAPI attribute is so that when the SET SESSION search_path directive is invoked, it is invoked outside of the scope of any transaction and therefore will not be reverted when the DBAPI connection has a rollback.

Remote-Schema Table Introspection and PostgreSQL search_path

Section Best Practices Summarized

keep the search_path variable set to its default of public, without any other schema names. Ensure the username used to connect does not match remote schemas, or ensure the "$user" token is removed from search_path. For other schema names, name these explicitly within Table definitions. Alternatively, the postgresql_ignore_search_path option will cause all reflected Table objects to have a Table.schema attribute set up.

The PostgreSQL dialect can reflect tables from any schema, as outlined in Reflecting Tables from Other Schemas.

In all cases, the first thing SQLAlchemy does when reflecting tables is to determine the default schema for the current database connection. It does this using the PostgreSQL current_schema() function, illustated below using a PostgreSQL client session (i.e. using the psql tool):

test=> select current_schema();
current_schema
----------------
public
(1 row)

Above we see that on a plain install of PostgreSQL, the default schema name is the name public.

However, if your database username matches the name of a schema, PostgreSQL’s default is to then use that name as the default schema. Below, we log in using the username scott. When we create a schema named scott, it implicitly changes the default schema:

test=> select current_schema();
current_schema
----------------
public
(1 row)

test=> create schema scott;
CREATE SCHEMA
test=> select current_schema();
current_schema
----------------
scott
(1 row)

The behavior of current_schema() is derived from the PostgreSQL search path variable search_path, which in modern PostgreSQL versions defaults to this:

test=> show search_path;
search_path
-----------------
"$user", public
(1 row)

Where above, the "$user" variable will inject the current username as the default schema, if one exists. Otherwise, public is used.

When a Table object is reflected, if it is present in the schema indicated by the current_schema() function, the schema name assigned to the “.schema” attribute of the Table is the Python “None” value. Otherwise, the “.schema” attribute will be assigned the string name of that schema.

With regards to tables which these Table objects refer to via foreign key constraint, a decision must be made as to how the .schema is represented in those remote tables, in the case where that remote schema name is also a member of the current search_path.

By default, the PostgreSQL dialect mimics the behavior encouraged by PostgreSQL’s own pg_get_constraintdef() builtin procedure. This function returns a sample definition for a particular foreign key constraint, omitting the referenced schema name from that definition when the name is also in the PostgreSQL schema search path. The interaction below illustrates this behavior:

test=> CREATE TABLE test_schema.referred(id INTEGER PRIMARY KEY);
CREATE TABLE
test=> CREATE TABLE referring(
test(>         id INTEGER PRIMARY KEY,
test(>         referred_id INTEGER REFERENCES test_schema.referred(id));
CREATE TABLE
test=> SET search_path TO public, test_schema;
test=> SELECT pg_catalog.pg_get_constraintdef(r.oid, true) FROM
test-> pg_catalog.pg_class c JOIN pg_catalog.pg_namespace n
test-> ON n.oid = c.relnamespace
test-> JOIN pg_catalog.pg_constraint r  ON c.oid = r.conrelid
test-> WHERE c.relname='referring' AND r.contype = 'f'
test-> ;
               pg_get_constraintdef
---------------------------------------------------
 FOREIGN KEY (referred_id) REFERENCES referred(id)
(1 row)

Above, we created a table referred as a member of the remote schema test_schema, however when we added test_schema to the PG search_path and then asked pg_get_constraintdef() for the FOREIGN KEY syntax, test_schema was not included in the output of the function.

On the other hand, if we set the search path back to the typical default of public:

test=> SET search_path TO public;
SET

The same query against pg_get_constraintdef() now returns the fully schema-qualified name for us:

test=> SELECT pg_catalog.pg_get_constraintdef(r.oid, true) FROM
test-> pg_catalog.pg_class c JOIN pg_catalog.pg_namespace n
test-> ON n.oid = c.relnamespace
test-> JOIN pg_catalog.pg_constraint r  ON c.oid = r.conrelid
test-> WHERE c.relname='referring' AND r.contype = 'f';
                     pg_get_constraintdef
---------------------------------------------------------------
 FOREIGN KEY (referred_id) REFERENCES test_schema.referred(id)
(1 row)

SQLAlchemy will by default use the return value of pg_get_constraintdef() in order to determine the remote schema name. That is, if our search_path were set to include test_schema, and we invoked a table reflection process as follows:

>>> from sqlalchemy import Table, MetaData, create_engine, text
>>> engine = create_engine("postgresql://scott:tiger@localhost/test")
>>> with engine.connect() as conn:
...     conn.execute(text("SET search_path TO test_schema, public"))
...     metadata_obj = MetaData()
...     referring = Table('referring', metadata_obj,
...                       autoload_with=conn)
...
<sqlalchemy.engine.result.CursorResult object at 0x101612ed0>

The above process would deliver to the MetaData.tables collection referred table named without the schema:

>>> metadata_obj.tables['referred'].schema is None
True

To alter the behavior of reflection such that the referred schema is maintained regardless of the search_path setting, use the postgresql_ignore_search_path option, which can be specified as a dialect-specific argument to both Table as well as MetaData.reflect():

>>> with engine.connect() as conn:
...     conn.execute(text("SET search_path TO test_schema, public"))
...     metadata_obj = MetaData()
...     referring = Table('referring', metadata_obj,
...                       autoload_with=conn,
...                       postgresql_ignore_search_path=True)
...
<sqlalchemy.engine.result.CursorResult object at 0x1016126d0>

We will now have test_schema.referred stored as schema-qualified:

>>> metadata_obj.tables['test_schema.referred'].schema
'test_schema'

See also

Interaction of Schema-qualified Reflection with the Default Schema - discussion of the issue from a backend-agnostic perspective

The Schema Search Path - on the PostgreSQL website.

INSERT/UPDATE…RETURNING

The dialect supports PG 8.2’s INSERT..RETURNING, UPDATE..RETURNING and DELETE..RETURNING syntaxes. INSERT..RETURNING is used by default for single-row INSERT statements in order to fetch newly generated primary key identifiers. To specify an explicit RETURNING clause, use the _UpdateBase.returning() method on a per-statement basis:

# INSERT..RETURNING
result = table.insert().returning(table.c.col1, table.c.col2).\
    values(name='foo')
print(result.fetchall())

# UPDATE..RETURNING
result = table.update().returning(table.c.col1, table.c.col2).\
    where(table.c.name=='foo').values(name='bar')
print(result.fetchall())

# DELETE..RETURNING
result = table.delete().returning(table.c.col1, table.c.col2).\
    where(table.c.name=='foo')
print(result.fetchall())

INSERT…ON CONFLICT (Upsert)

Starting with version 9.5, PostgreSQL allows “upserts” (update or insert) of rows into a table via the ON CONFLICT clause of the INSERT statement. A candidate row will only be inserted if that row does not violate any unique constraints. In the case of a unique constraint violation, a secondary action can occur which can be either “DO UPDATE”, indicating that the data in the target row should be updated, or “DO NOTHING”, which indicates to silently skip this row.

Conflicts are determined using existing unique constraints and indexes. These constraints may be identified either using their name as stated in DDL, or they may be inferred by stating the columns and conditions that comprise the indexes.

SQLAlchemy provides ON CONFLICT support via the PostgreSQL-specific insert() function, which provides the generative methods Insert.on_conflict_do_update() and Insert.on_conflict_do_nothing():

>>> from sqlalchemy.dialects.postgresql import insert
>>> insert_stmt = insert(my_table).values(
...     id='some_existing_id',
...     data='inserted value')
>>> do_nothing_stmt = insert_stmt.on_conflict_do_nothing(
...     index_elements=['id']
... )
>>> print(do_nothing_stmt)
INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s) ON CONFLICT (id) DO NOTHING
>>> do_update_stmt = insert_stmt.on_conflict_do_update( ... constraint='pk_my_table', ... set_=dict(data='updated value') ... ) >>> print(do_update_stmt)
INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s) ON CONFLICT ON CONSTRAINT pk_my_table DO UPDATE SET data = %(param_1)s

New in version 1.1.

See also

INSERT .. ON CONFLICT - in the PostgreSQL documentation.

Specifying the Target

Both methods supply the “target” of the conflict using either the named constraint or by column inference:

  • The Insert.on_conflict_do_update.index_elements argument specifies a sequence containing string column names, Column objects, and/or SQL expression elements, which would identify a unique index:

    >>> do_update_stmt = insert_stmt.on_conflict_do_update(
    ...     index_elements=['id'],
    ...     set_=dict(data='updated value')
    ... )
    >>> print(do_update_stmt)
    
    INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s) ON CONFLICT (id) DO UPDATE SET data = %(param_1)s
    >>> do_update_stmt = insert_stmt.on_conflict_do_update( ... index_elements=[my_table.c.id], ... set_=dict(data='updated value') ... ) >>> print(do_update_stmt)
    INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s) ON CONFLICT (id) DO UPDATE SET data = %(param_1)s
  • When using Insert.on_conflict_do_update.index_elements to infer an index, a partial index can be inferred by also specifying the use the Insert.on_conflict_do_update.index_where parameter:

    >>> stmt = insert(my_table).values(user_email='a@b.com', data='inserted data')
    >>> stmt = stmt.on_conflict_do_update(
    ...     index_elements=[my_table.c.user_email],
    ...     index_where=my_table.c.user_email.like('%@gmail.com'),
    ...     set_=dict(data=stmt.excluded.data)
    ... )
    >>> print(stmt)
    
    INSERT INTO my_table (data, user_email) VALUES (%(data)s, %(user_email)s) ON CONFLICT (user_email) WHERE user_email LIKE %(user_email_1)s DO UPDATE SET data = excluded.data
  • The Insert.on_conflict_do_update.constraint argument is used to specify an index directly rather than inferring it. This can be the name of a UNIQUE constraint, a PRIMARY KEY constraint, or an INDEX:

    >>> do_update_stmt = insert_stmt.on_conflict_do_update(
    ...     constraint='my_table_idx_1',
    ...     set_=dict(data='updated value')
    ... )
    >>> print(do_update_stmt)
    
    INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s) ON CONFLICT ON CONSTRAINT my_table_idx_1 DO UPDATE SET data = %(param_1)s
    >>> do_update_stmt = insert_stmt.on_conflict_do_update( ... constraint='my_table_pk', ... set_=dict(data='updated value') ... ) >>> print(do_update_stmt)
    INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s) ON CONFLICT ON CONSTRAINT my_table_pk DO UPDATE SET data = %(param_1)s
  • The Insert.on_conflict_do_update.constraint argument may also refer to a SQLAlchemy construct representing a constraint, e.g. UniqueConstraint, PrimaryKeyConstraint, Index, or ExcludeConstraint. In this use, if the constraint has a name, it is used directly. Otherwise, if the constraint is unnamed, then inference will be used, where the expressions and optional WHERE clause of the constraint will be spelled out in the construct. This use is especially convenient to refer to the named or unnamed primary key of a Table using the Table.primary_key attribute:

    >>> do_update_stmt = insert_stmt.on_conflict_do_update(
    ...     constraint=my_table.primary_key,
    ...     set_=dict(data='updated value')
    ... )
    >>> print(do_update_stmt)
    
    INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s) ON CONFLICT (id) DO UPDATE SET data = %(param_1)s

The SET Clause

ON CONFLICT...DO UPDATE is used to perform an update of the already existing row, using any combination of new values as well as values from the proposed insertion. These values are specified using the Insert.on_conflict_do_update.set_ parameter. This parameter accepts a dictionary which consists of direct values for UPDATE:

>>> stmt = insert(my_table).values(id='some_id', data='inserted value')
>>> do_update_stmt = stmt.on_conflict_do_update(
...     index_elements=['id'],
...     set_=dict(data='updated value')
... )
>>> print(do_update_stmt)
INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s) ON CONFLICT (id) DO UPDATE SET data = %(param_1)s

Warning

The Insert.on_conflict_do_update() method does not take into account Python-side default UPDATE values or generation functions, e.g. those specified using Column.onupdate. These values will not be exercised for an ON CONFLICT style of UPDATE, unless they are manually specified in the Insert.on_conflict_do_update.set_ dictionary.

Updating using the Excluded INSERT Values

In order to refer to the proposed insertion row, the special alias Insert.excluded is available as an attribute on the Insert object; this object is a ColumnCollection which alias contains all columns of the target table:

>>> stmt = insert(my_table).values(
...     id='some_id',
...     data='inserted value',
...     author='jlh'
... )
>>> do_update_stmt = stmt.on_conflict_do_update(
...     index_elements=['id'],
...     set_=dict(data='updated value', author=stmt.excluded.author)
... )
>>> print(do_update_stmt)
INSERT INTO my_table (id, data, author) VALUES (%(id)s, %(data)s, %(author)s) ON CONFLICT (id) DO UPDATE SET data = %(param_1)s, author = excluded.author

Additional WHERE Criteria

The Insert.on_conflict_do_update() method also accepts a WHERE clause using the Insert.on_conflict_do_update.where parameter, which will limit those rows which receive an UPDATE:

>>> stmt = insert(my_table).values(
...     id='some_id',
...     data='inserted value',
...     author='jlh'
... )
>>> on_update_stmt = stmt.on_conflict_do_update(
...     index_elements=['id'],
...     set_=dict(data='updated value', author=stmt.excluded.author),
...     where=(my_table.c.status == 2)
... )
>>> print(on_update_stmt)
INSERT INTO my_table (id, data, author) VALUES (%(id)s, %(data)s, %(author)s) ON CONFLICT (id) DO UPDATE SET data = %(param_1)s, author = excluded.author WHERE my_table.status = %(status_1)s

Skipping Rows with DO NOTHING

ON CONFLICT may be used to skip inserting a row entirely if any conflict with a unique or exclusion constraint occurs; below this is illustrated using the Insert.on_conflict_do_nothing() method:

>>> stmt = insert(my_table).values(id='some_id', data='inserted value')
>>> stmt = stmt.on_conflict_do_nothing(index_elements=['id'])
>>> print(stmt)
INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s) ON CONFLICT (id) DO NOTHING

If DO NOTHING is used without specifying any columns or constraint, it has the effect of skipping the INSERT for any unique or exclusion constraint violation which occurs:

>>> stmt = insert(my_table).values(id='some_id', data='inserted value')
>>> stmt = stmt.on_conflict_do_nothing()
>>> print(stmt)
INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s) ON CONFLICT DO NOTHING

FROM ONLY …

The dialect supports PostgreSQL’s ONLY keyword for targeting only a particular table in an inheritance hierarchy. This can be used to produce the SELECT ... FROM ONLY, UPDATE ONLY ..., and DELETE FROM ONLY ... syntaxes. It uses SQLAlchemy’s hints mechanism:

# SELECT ... FROM ONLY ...
result = table.select().with_hint(table, 'ONLY', 'postgresql')
print(result.fetchall())

# UPDATE ONLY ...
table.update(values=dict(foo='bar')).with_hint('ONLY',
                                               dialect_name='postgresql')

# DELETE FROM ONLY ...
table.delete().with_hint('ONLY', dialect_name='postgresql')

PostgreSQL-Specific Index Options

Several extensions to the Index construct are available, specific to the PostgreSQL dialect.

Covering Indexes

The postgresql_include option renders INCLUDE(colname) for the given string names:

Index("my_index", table.c.x, postgresql_include=['y'])

would render the index as CREATE INDEX my_index ON table (x) INCLUDE (y)

Note that this feature requires PostgreSQL 11 or later.

New in version 1.4.

Partial Indexes

Partial indexes add criterion to the index definition so that the index is applied to a subset of rows. These can be specified on Index using the postgresql_where keyword argument:

Index('my_index', my_table.c.id, postgresql_where=my_table.c.value > 10)

Operator Classes

PostgreSQL allows the specification of an operator class for each column of an index (see https://www.postgresql.org/docs/current/interactive/indexes-opclass.html). The Index construct allows these to be specified via the postgresql_ops keyword argument:

Index(
    'my_index', my_table.c.id, my_table.c.data,
    postgresql_ops={
        'data': 'text_pattern_ops',
        'id': 'int4_ops'
    })

Note that the keys in the postgresql_ops dictionaries are the “key” name of the Column, i.e. the name used to access it from the .c collection of Table, which can be configured to be different than the actual name of the column as expressed in the database.

If postgresql_ops is to be used against a complex SQL expression such as a function call, then to apply to the column it must be given a label that is identified in the dictionary by name, e.g.:

Index(
    'my_index', my_table.c.id,
    func.lower(my_table.c.data).label('data_lower'),
    postgresql_ops={
        'data_lower': 'text_pattern_ops',
        'id': 'int4_ops'
    })

Operator classes are also supported by the ExcludeConstraint construct using the ExcludeConstraint.ops parameter. See that parameter for details.

New in version 1.3.21: added support for operator classes with ExcludeConstraint.

Index Types

PostgreSQL provides several index types: B-Tree, Hash, GiST, and GIN, as well as the ability for users to create their own (see https://www.postgresql.org/docs/current/static/indexes-types.html). These can be specified on Index using the postgresql_using keyword argument:

Index('my_index', my_table.c.data, postgresql_using='gin')

The value passed to the keyword argument will be simply passed through to the underlying CREATE INDEX command, so it must be a valid index type for your version of PostgreSQL.

Index Storage Parameters

PostgreSQL allows storage parameters to be set on indexes. The storage parameters available depend on the index method used by the index. Storage parameters can be specified on Index using the postgresql_with keyword argument:

Index('my_index', my_table.c.data, postgresql_with={"fillfactor": 50})

New in version 1.0.6.

PostgreSQL allows to define the tablespace in which to create the index. The tablespace can be specified on Index using the postgresql_tablespace keyword argument:

Index('my_index', my_table.c.data, postgresql_tablespace='my_tablespace')

New in version 1.1.

Note that the same option is available on Table as well.

Indexes with CONCURRENTLY

The PostgreSQL index option CONCURRENTLY is supported by passing the flag postgresql_concurrently to the Index construct:

tbl = Table('testtbl', m, Column('data', Integer))

idx1 = Index('test_idx1', tbl.c.data, postgresql_concurrently=True)

The above index construct will render DDL for CREATE INDEX, assuming PostgreSQL 8.2 or higher is detected or for a connection-less dialect, as:

CREATE INDEX CONCURRENTLY test_idx1 ON testtbl (data)

For DROP INDEX, assuming PostgreSQL 9.2 or higher is detected or for a connection-less dialect, it will emit:

DROP INDEX CONCURRENTLY test_idx1

New in version 1.1: support for CONCURRENTLY on DROP INDEX. The CONCURRENTLY keyword is now only emitted if a high enough version of PostgreSQL is detected on the connection (or for a connection-less dialect).

When using CONCURRENTLY, the PostgreSQL database requires that the statement be invoked outside of a transaction block. The Python DBAPI enforces that even for a single statement, a transaction is present, so to use this construct, the DBAPI’s “autocommit” mode must be used:

metadata = MetaData()
table = Table(
    "foo", metadata,
    Column("id", String))
index = Index(
    "foo_idx", table.c.id, postgresql_concurrently=True)

with engine.connect() as conn:
    with conn.execution_options(isolation_level='AUTOCOMMIT'):
        table.create(conn)

PostgreSQL Index Reflection

The PostgreSQL database creates a UNIQUE INDEX implicitly whenever the UNIQUE CONSTRAINT construct is used. When inspecting a table using Inspector, the Inspector.get_indexes() and the Inspector.get_unique_constraints() will report on these two constructs distinctly; in the case of the index, the key duplicates_constraint will be present in the index entry if it is detected as mirroring a constraint. When performing reflection using Table(..., autoload_with=engine), the UNIQUE INDEX is not returned in Table.indexes when it is detected as mirroring a UniqueConstraint in the Table.constraints collection .

Changed in version 1.0.0: - Table reflection now includes UniqueConstraint objects present in the Table.constraints collection; the PostgreSQL backend will no longer include a “mirrored” Index construct in Table.indexes if it is detected as corresponding to a unique constraint.

Special Reflection Options

The Inspector used for the PostgreSQL backend is an instance of PGInspector, which offers additional methods:

from sqlalchemy import create_engine, inspect

engine = create_engine("postgresql+psycopg2://localhost/test")
insp = inspect(engine)  # will be a PGInspector

print(insp.get_enums())
Object Name Description

PGInspector

class sqlalchemy.dialects.postgresql.base.PGInspector(bind)
method sqlalchemy.dialects.postgresql.base.PGInspector.get_enums(schema=None)

Return a list of ENUM objects.

Each member is a dictionary containing these fields:

  • name - name of the enum

  • schema - the schema name for the enum.

  • visible - boolean, whether or not this enum is visible in the default search path.

  • labels - a list of string labels that apply to the enum.

Parameters:

schema – schema name. If None, the default schema (typically ‘public’) is used. May also be set to ‘*’ to indicate load enums for all schemas.

New in version 1.0.0.

method sqlalchemy.dialects.postgresql.base.PGInspector.get_foreign_table_names(schema=None)

Return a list of FOREIGN TABLE names.

Behavior is similar to that of Inspector.get_table_names(), except that the list is limited to those tables that report a relkind value of f.

New in version 1.0.0.

method sqlalchemy.dialects.postgresql.base.PGInspector.get_table_oid(table_name, schema=None)

Return the OID for the given table name.

method sqlalchemy.dialects.postgresql.base.PGInspector.get_view_names(schema=None, include=('plain', 'materialized'))

Return all view names in schema.

Parameters:
  • schema – Optional, retrieve names from a non-default schema. For special quoting, use quoted_name.

  • include

    specify which types of views to return. Passed as a string value (for a single type) or a tuple (for any number of types). Defaults to ('plain', 'materialized').

    New in version 1.1.

PostgreSQL Table Options

Several options for CREATE TABLE are supported directly by the PostgreSQL dialect in conjunction with the Table construct:

  • TABLESPACE:

    Table("some_table", metadata, ..., postgresql_tablespace='some_tablespace')

    The above option is also available on the Index construct.

  • ON COMMIT:

    Table("some_table", metadata, ..., postgresql_on_commit='PRESERVE ROWS')
  • WITH OIDS:

    Table("some_table", metadata, ..., postgresql_with_oids=True)
  • WITHOUT OIDS:

    Table("some_table", metadata, ..., postgresql_with_oids=False)
  • INHERITS:

    Table("some_table", metadata, ..., postgresql_inherits="some_supertable")
    
    Table("some_table", metadata, ..., postgresql_inherits=("t1", "t2", ...))
    
    .. versionadded:: 1.0.0
  • PARTITION BY:

    Table("some_table", metadata, ...,
          postgresql_partition_by='LIST (part_column)')
    
    .. versionadded:: 1.2.6

See also

PostgreSQL CREATE TABLE options - in the PostgreSQL documentation.

PostgreSQL Constraint Options

The following option(s) are supported by the PostgreSQL dialect in conjunction with selected constraint constructs:

  • NOT VALID: This option applies towards CHECK and FOREIGN KEY constraints when the constraint is being added to an existing table via ALTER TABLE, and has the effect that existing rows are not scanned during the ALTER operation against the constraint being added.

    When using a SQL migration tool such as Alembic that renders ALTER TABLE constructs, the postgresql_not_valid argument may be specified as an additional keyword argument within the operation that creates the constraint, as in the following Alembic example:

    def update():
        op.create_foreign_key(
            "fk_user_address",
            "address",
            "user",
            ["user_id"],
            ["id"],
            postgresql_not_valid=True
        )

    The keyword is ultimately accepted directly by the CheckConstraint, ForeignKeyConstraint and ForeignKey constructs; when using a tool like Alembic, dialect-specific keyword arguments are passed through to these constructs from the migration operation directives:

    CheckConstraint("some_field IS NOT NULL", postgresql_not_valid=True)
    
    ForeignKeyConstraint(["some_id"], ["some_table.some_id"], postgresql_not_valid=True)

    New in version 1.4.32.

    See also

    PostgreSQL ALTER TABLE options - in the PostgreSQL documentation.

Table values, Table and Column valued functions, Row and Tuple objects

PostgreSQL makes great use of modern SQL forms such as table-valued functions, tables and rows as values. These constructs are commonly used as part of PostgreSQL’s support for complex datatypes such as JSON, ARRAY, and other datatypes. SQLAlchemy’s SQL expression language has native support for most table-valued and row-valued forms.

Table-Valued Functions

Many PostgreSQL built-in functions are intended to be used in the FROM clause of a SELECT statement, and are capable of returning table rows or sets of table rows. A large portion of PostgreSQL’s JSON functions for example such as json_array_elements(), json_object_keys(), json_each_text(), json_each(), json_to_record(), json_populate_recordset() use such forms. These classes of SQL function calling forms in SQLAlchemy are available using the FunctionElement.table_valued() method in conjunction with Function objects generated from the func namespace.

Examples from PostgreSQL’s reference documentation follow below:

  • json_each():

    >>> from sqlalchemy import select, func
    >>> stmt = select(func.json_each('{"a":"foo", "b":"bar"}').table_valued("key", "value"))
    >>> print(stmt)
    SELECT anon_1.key, anon_1.value
    FROM json_each(:json_each_1) AS anon_1
  • json_populate_record():

    >>> from sqlalchemy import select, func, literal_column
    >>> stmt = select(
    ...     func.json_populate_record(
    ...         literal_column("null::myrowtype"),
    ...         '{"a":1,"b":2}'
    ...     ).table_valued("a", "b", name="x")
    ... )
    >>> print(stmt)
    SELECT x.a, x.b
    FROM json_populate_record(null::myrowtype, :json_populate_record_1) AS x
  • json_to_record() - this form uses a PostgreSQL specific form of derived columns in the alias, where we may make use of column() elements with types to produce them. The FunctionElement.table_valued() method produces a TableValuedAlias construct, and the method TableValuedAlias.render_derived() method sets up the derived columns specification:

    >>> from sqlalchemy import select, func, column, Integer, Text
    >>> stmt = select(
    ...     func.json_to_record('{"a":1,"b":[1,2,3],"c":"bar"}').table_valued(
    ...         column("a", Integer), column("b", Text), column("d", Text),
    ...     ).render_derived(name="x", with_types=True)
    ... )
    >>> print(stmt)
    SELECT x.a, x.b, x.d
    FROM json_to_record(:json_to_record_1) AS x(a INTEGER, b TEXT, d TEXT)
  • WITH ORDINALITY - part of the SQL standard, WITH ORDINALITY adds an ordinal counter to the output of a function and is accepted by a limited set of PostgreSQL functions including unnest() and generate_series(). The FunctionElement.table_valued() method accepts a keyword parameter with_ordinality for this purpose, which accepts the string name that will be applied to the “ordinality” column:

    >>> from sqlalchemy import select, func
    >>> stmt = select(
    ...     func.generate_series(4, 1, -1).
    ...     table_valued("value", with_ordinality="ordinality").
    ...     render_derived()
    ... )
    >>> print(stmt)
    SELECT anon_1.value, anon_1.ordinality
    FROM generate_series(:generate_series_1, :generate_series_2, :generate_series_3)
    WITH ORDINALITY AS anon_1(value, ordinality)

New in version 1.4.0b2.

Column Valued Functions

Similar to the table valued function, a column valued function is present in the FROM clause, but delivers itself to the columns clause as a single scalar value. PostgreSQL functions such as json_array_elements(), unnest() and generate_series() may use this form. Column valued functions are available using the FunctionElement.column_valued() method of FunctionElement:

  • json_array_elements():

    >>> from sqlalchemy import select, func
    >>> stmt = select(func.json_array_elements('["one", "two"]').column_valued("x"))
    >>> print(stmt)
    SELECT x
    FROM json_array_elements(:json_array_elements_1) AS x
  • unnest() - in order to generate a PostgreSQL ARRAY literal, the array() construct may be used:

    >>> from sqlalchemy.dialects.postgresql import array
    >>> from sqlalchemy import select, func
    >>> stmt = select(func.unnest(array([1, 2])).column_valued())
    >>> print(stmt)
    SELECT anon_1
    FROM unnest(ARRAY[%(param_1)s, %(param_2)s]) AS anon_1

    The function can of course be used against an existing table-bound column that’s of type ARRAY:

    >>> from sqlalchemy import table, column, ARRAY, Integer
    >>> from sqlalchemy import select, func
    >>> t = table("t", column('value', ARRAY(Integer)))
    >>> stmt = select(func.unnest(t.c.value).column_valued("unnested_value"))
    >>> print(stmt)
    SELECT unnested_value
    FROM unnest(t.value) AS unnested_value

Row Types

Built-in support for rendering a ROW may be approximated using func.ROW with the sqlalchemy.func namespace, or by using the tuple_() construct:

>>> from sqlalchemy import table, column, func, tuple_
>>> t = table("t", column("id"), column("fk"))
>>> stmt = t.select().where(
...     tuple_(t.c.id, t.c.fk) > (1,2)
... ).where(
...     func.ROW(t.c.id, t.c.fk) < func.ROW(3, 7)
... )
>>> print(stmt)
SELECT t.id, t.fk
FROM t
WHERE (t.id, t.fk) > (:param_1, :param_2) AND ROW(t.id, t.fk) < ROW(:ROW_1, :ROW_2)

Table Types passed to Functions

PostgreSQL supports passing a table as an argument to a function, which it refers towards as a “record” type. SQLAlchemy FromClause objects such as Table support this special form using the FromClause.table_valued() method, which is comparable to the FunctionElement.table_valued() method except that the collection of columns is already established by that of the FromClause itself:

>>> from sqlalchemy import table, column, func, select
>>> a = table( "a", column("id"), column("x"), column("y"))
>>> stmt = select(func.row_to_json(a.table_valued()))
>>> print(stmt)
SELECT row_to_json(a) AS row_to_json_1
FROM a

New in version 1.4.0b2.

ARRAY Types

The PostgreSQL dialect supports arrays, both as multidimensional column types as well as array literals:

JSON Types

The PostgreSQL dialect supports both JSON and JSONB datatypes, including psycopg2’s native support and support for all of PostgreSQL’s special operators:

HSTORE Type

The PostgreSQL HSTORE type as well as hstore literals are supported:

ENUM Types

PostgreSQL has an independently creatable TYPE structure which is used to implement an enumerated type. This approach introduces significant complexity on the SQLAlchemy side in terms of when this type should be CREATED and DROPPED. The type object is also an independently reflectable entity. The following sections should be consulted:

Using ENUM with ARRAY

The combination of ENUM and ARRAY is not directly supported by backend DBAPIs at this time. Prior to SQLAlchemy 1.3.17, a special workaround was needed in order to allow this combination to work, described below.

Changed in version 1.3.17: The combination of ENUM and ARRAY is now directly handled by SQLAlchemy’s implementation without any workarounds needed.

from sqlalchemy import TypeDecorator
from sqlalchemy.dialects.postgresql import ARRAY

class ArrayOfEnum(TypeDecorator):
    impl = ARRAY

    def bind_expression(self, bindvalue):
        return sa.cast(bindvalue, self)

    def result_processor(self, dialect, coltype):
        super_rp = super(ArrayOfEnum, self).result_processor(
            dialect, coltype)

        def handle_raw_string(value):
            inner = re.match(r"^{(.*)}$", value).group(1)
            return inner.split(",") if inner else []

        def process(value):
            if value is None:
                return None
            return super_rp(handle_raw_string(value))
        return process

E.g.:

Table(
    'mydata', metadata,
    Column('id', Integer, primary_key=True),
    Column('data', ArrayOfEnum(ENUM('a', 'b, 'c', name='myenum')))

)

This type is not included as a built-in type as it would be incompatible with a DBAPI that suddenly decides to support ARRAY of ENUM directly in a new version.

Using JSON/JSONB with ARRAY

Similar to using ENUM, prior to SQLAlchemy 1.3.17, for an ARRAY of JSON/JSONB we need to render the appropriate CAST. Current psycopg2 drivers accommodate the result set correctly without any special steps.

Changed in version 1.3.17: The combination of JSON/JSONB and ARRAY is now directly handled by SQLAlchemy’s implementation without any workarounds needed.

class CastingArray(ARRAY):
    def bind_expression(self, bindvalue):
        return sa.cast(bindvalue, self)

E.g.:

Table(
    'mydata', metadata,
    Column('id', Integer, primary_key=True),
    Column('data', CastingArray(JSONB))
)

PostgreSQL Data Types and Custom SQL Constructs

As with all SQLAlchemy dialects, all UPPERCASE types that are known to be valid with PostgreSQL are importable from the top level dialect, whether they originate from sqlalchemy.types or from the local dialect:

from sqlalchemy.dialects.postgresql import (
    ARRAY,
    BIGINT,
    BIT,
    BOOLEAN,
    BYTEA,
    CHAR,
    CIDR,
    DATE,
    DOUBLE_PRECISION,
    ENUM,
    FLOAT,
    HSTORE,
    INET,
    INTEGER,
    INTERVAL,
    JSON,
    JSONB,
    MACADDR,
    MACADDR8,
    MONEY,
    NUMERIC,
    OID,
    REAL,
    SMALLINT,
    TEXT,
    TIME,
    TIMESTAMP,
    UUID,
    VARCHAR,
    INT4RANGE,
    INT8RANGE,
    NUMRANGE,
    DATERANGE,
    TSRANGE,
    TSTZRANGE,
    TSVECTOR,
)

Types which are specific to PostgreSQL, or have PostgreSQL-specific construction arguments, are as follows:

Object Name Description

aggregate_order_by

Represent a PostgreSQL aggregate order by expression.

All(other, arrexpr[, operator])

A synonym for the ARRAY-level Comparator.all() method. See that method for details.

Any(other, arrexpr[, operator])

A synonym for the ARRAY-level Comparator.any() method. See that method for details.

array

A PostgreSQL ARRAY literal.

ARRAY

PostgreSQL ARRAY type.

array_agg(*arg, **kw)

PostgreSQL-specific form of array_agg, ensures return type is ARRAY and not the plain ARRAY, unless an explicit type_ is passed.

BIT

BYTEA

CIDR

ENUM

PostgreSQL ENUM type.

HSTORE

Represent the PostgreSQL HSTORE type.

hstore

Construct an hstore value within a SQL expression using the PostgreSQL hstore() function.

INET

INTERVAL

PostgreSQL INTERVAL type.

JSON

Represent the PostgreSQL JSON type.

JSONB

Represent the PostgreSQL JSONB type.

MACADDR

MACADDR8

MONEY

Provide the PostgreSQL MONEY type.

OID

Provide the PostgreSQL OID type.

REGCLASS

Provide the PostgreSQL REGCLASS type.

TIME

PostgreSQL TIME type.

TIMESTAMP

Provide the PostgreSQL TIMESTAMP type.

TSVECTOR

The TSVECTOR type implements the PostgreSQL text search type TSVECTOR.

UUID

PostgreSQL UUID type.

class sqlalchemy.dialects.postgresql.aggregate_order_by(target, *order_by)

Represent a PostgreSQL aggregate order by expression.

E.g.:

from sqlalchemy.dialects.postgresql import aggregate_order_by
expr = func.array_agg(aggregate_order_by(table.c.a, table.c.b.desc()))
stmt = select(expr)

would represent the expression:

SELECT array_agg(a ORDER BY b DESC) FROM table;

Similarly:

expr = func.string_agg(
    table.c.a,
    aggregate_order_by(literal_column("','"), table.c.a)
)
stmt = select(expr)

Would represent:

SELECT string_agg(a, ',' ORDER BY a) FROM table;

New in version 1.1.

Changed in version 1.2.13: - the ORDER BY argument may be multiple terms

See also

array_agg

class sqlalchemy.dialects.postgresql.array(clauses, **kw)

A PostgreSQL ARRAY literal.

This is used to produce ARRAY literals in SQL expressions, e.g.:

from sqlalchemy.dialects.postgresql import array
from sqlalchemy.dialects import postgresql
from sqlalchemy import select, func

stmt = select(array([1,2]) + array([3,4,5]))

print(stmt.compile(dialect=postgresql.dialect()))

Produces the SQL:

SELECT ARRAY[%(param_1)s, %(param_2)s] ||
    ARRAY[%(param_3)s, %(param_4)s, %(param_5)s]) AS anon_1

An instance of array will always have the datatype ARRAY. The “inner” type of the array is inferred from the values present, unless the type_ keyword argument is passed:

array(['foo', 'bar'], type_=CHAR)

Multidimensional arrays are produced by nesting array constructs. The dimensionality of the final ARRAY type is calculated by recursively adding the dimensions of the inner ARRAY type:

stmt = select(
    array([
        array([1, 2]), array([3, 4]), array([column('q'), column('x')])
    ])
)
print(stmt.compile(dialect=postgresql.dialect()))

Produces:

SELECT ARRAY[ARRAY[%(param_1)s, %(param_2)s],
ARRAY[%(param_3)s, %(param_4)s], ARRAY[q, x]] AS anon_1

New in version 1.3.6: added support for multidimensional array literals

See also

ARRAY

class sqlalchemy.dialects.postgresql.ARRAY(item_type, as_tuple=False, dimensions=None, zero_indexes=False)

PostgreSQL ARRAY type.

Changed in version 1.1: The ARRAY type is now a subclass of the core ARRAY type.

The ARRAY type is constructed in the same way as the core ARRAY type; a member type is required, and a number of dimensions is recommended if the type is to be used for more than one dimension:

from sqlalchemy.dialects import postgresql

mytable = Table("mytable", metadata,
        Column("data", postgresql.ARRAY(Integer, dimensions=2))
    )

The ARRAY type provides all operations defined on the core ARRAY type, including support for “dimensions”, indexed access, and simple matching such as Comparator.any() and Comparator.all(). ARRAY class also provides PostgreSQL-specific methods for containment operations, including Comparator.contains() Comparator.contained_by(), and Comparator.overlap(), e.g.:

mytable.c.data.contains([1, 2])

The ARRAY type may not be supported on all PostgreSQL DBAPIs; it is currently known to work on psycopg2 only.

Additionally, the ARRAY type does not work directly in conjunction with the ENUM type. For a workaround, see the special type at Using ENUM with ARRAY.

Detecting Changes in ARRAY columns when using the ORM

The ARRAY type, when used with the SQLAlchemy ORM, does not detect in-place mutations to the array. In order to detect these, the sqlalchemy.ext.mutable extension must be used, using the MutableList class:

from sqlalchemy.dialects.postgresql import ARRAY
from sqlalchemy.ext.mutable import MutableList

class SomeOrmClass(Base):
    # ...

    data = Column(MutableList.as_mutable(ARRAY(Integer)))

This extension will allow “in-place” changes such to the array such as .append() to produce events which will be detected by the unit of work. Note that changes to elements inside the array, including subarrays that are mutated in place, are not detected.

Alternatively, assigning a new array value to an ORM element that replaces the old one will always trigger a change event.

See also

ARRAY - base array type

array - produces a literal array value.

class Comparator(expr)

Define comparison operations for ARRAY.

Note that these operations are in addition to those provided by the base Comparator class, including Comparator.any() and Comparator.all().

Class signature

class sqlalchemy.dialects.postgresql.ARRAY.Comparator (sqlalchemy.types.Comparator)

method sqlalchemy.dialects.postgresql.ARRAY.Comparator.contained_by(other)

Boolean expression. Test if elements are a proper subset of the elements of the argument array expression.

method sqlalchemy.dialects.postgresql.ARRAY.Comparator.contains(other, **kwargs)

Boolean expression. Test if elements are a superset of the elements of the argument array expression.

kwargs may be ignored by this operator but are required for API conformance.

method sqlalchemy.dialects.postgresql.ARRAY.Comparator.overlap(other)

Boolean expression. Test if array has elements in common with an argument array expression.

method sqlalchemy.dialects.postgresql.ARRAY.__init__(item_type, as_tuple=False, dimensions=None, zero_indexes=False)

Construct an ARRAY.

E.g.:

Column('myarray', ARRAY(Integer))

Arguments are:

Parameters:
  • item_type – The data type of items of this array. Note that dimensionality is irrelevant here, so multi-dimensional arrays like INTEGER[][], are constructed as ARRAY(Integer), not as ARRAY(ARRAY(Integer)) or such.

  • as_tuple=False – Specify whether return results should be converted to tuples from lists. DBAPIs such as psycopg2 return lists by default. When tuples are returned, the results are hashable.

  • dimensions – if non-None, the ARRAY will assume a fixed number of dimensions. This will cause the DDL emitted for this ARRAY to include the exact number of bracket clauses [], and will also optimize the performance of the type overall. Note that PG arrays are always implicitly “non-dimensioned”, meaning they can store any number of dimensions no matter how they were declared.

  • zero_indexes=False

    when True, index values will be converted between Python zero-based and PostgreSQL one-based indexes, e.g. a value of one will be added to all index values before passing to the database.

    New in version 0.9.5.

function sqlalchemy.dialects.postgresql.array_agg(*arg, **kw)

PostgreSQL-specific form of array_agg, ensures return type is ARRAY and not the plain ARRAY, unless an explicit type_ is passed.

New in version 1.1.

function sqlalchemy.dialects.postgresql.Any(other, arrexpr, operator=<built-in function eq>)

A synonym for the ARRAY-level Comparator.any() method. See that method for details.

function sqlalchemy.dialects.postgresql.All(other, arrexpr, operator=<built-in function eq>)

A synonym for the ARRAY-level Comparator.all() method. See that method for details.

class sqlalchemy.dialects.postgresql.BIT(length=None, varying=False)
class sqlalchemy.dialects.postgresql.BYTEA(length=None)

Members

__init__()

method sqlalchemy.dialects.postgresql.BYTEA.__init__(length=None)

inherited from the sqlalchemy.types.LargeBinary.__init__ method of LargeBinary

Construct a LargeBinary type.

Parameters:

length – optional, a length for the column for use in DDL statements, for those binary types that accept a length, such as the MySQL BLOB type.

class sqlalchemy.dialects.postgresql.CIDR
class sqlalchemy.dialects.postgresql.DOUBLE_PRECISION(precision=None, asdecimal=False, decimal_return_scale=None)

Class signature

class sqlalchemy.dialects.postgresql.DOUBLE_PRECISION (sqlalchemy.types.Float)

method sqlalchemy.dialects.postgresql.DOUBLE_PRECISION.__init__(precision=None, asdecimal=False, decimal_return_scale=None)

inherited from the sqlalchemy.types.Float.__init__ method of Float

Construct a Float.

Parameters:
  • precision – the numeric precision for use in DDL CREATE TABLE.

  • asdecimal – the same flag as that of Numeric, but defaults to False. Note that setting this flag to True results in floating point conversion.

  • decimal_return_scale

    Default scale to use when converting from floats to Python decimals. Floating point values will typically be much longer due to decimal inaccuracy, and most floating point database types don’t have a notion of “scale”, so by default the float type looks for the first ten decimal places when converting. Specifying this value will override that length. Note that the MySQL float types, which do include “scale”, will use “scale” as the default for decimal_return_scale, if not otherwise specified.

    New in version 0.9.0.

class sqlalchemy.dialects.postgresql.ENUM(*enums, **kw)

PostgreSQL ENUM type.

This is a subclass of Enum which includes support for PG’s CREATE TYPE and DROP TYPE.

When the builtin type Enum is used and the Enum.native_enum flag is left at its default of True, the PostgreSQL backend will use a ENUM type as the implementation, so the special create/drop rules will be used.

The create/drop behavior of ENUM is necessarily intricate, due to the awkward relationship the ENUM type has in relationship to the parent table, in that it may be “owned” by just a single table, or may be shared among many tables.

When using Enum or ENUM in an “inline” fashion, the CREATE TYPE and DROP TYPE is emitted corresponding to when the Table.create() and Table.drop() methods are called:

table = Table('sometable', metadata,
    Column('some_enum', ENUM('a', 'b', 'c', name='myenum'))
)

table.create(engine)  # will emit CREATE ENUM and CREATE TABLE
table.drop(engine)  # will emit DROP TABLE and DROP ENUM

To use a common enumerated type between multiple tables, the best practice is to declare the Enum or ENUM independently, and associate it with the MetaData object itself:

my_enum = ENUM('a', 'b', 'c', name='myenum', metadata=metadata)

t1 = Table('sometable_one', metadata,
    Column('some_enum', myenum)
)

t2 = Table('sometable_two', metadata,
    Column('some_enum', myenum)
)

When this pattern is used, care must still be taken at the level of individual table creates. Emitting CREATE TABLE without also specifying checkfirst=True will still cause issues:

t1.create(engine) # will fail: no such type 'myenum'

If we specify checkfirst=True, the individual table-level create operation will check for the ENUM and create if not exists:

# will check if enum exists, and emit CREATE TYPE if not
t1.create(engine, checkfirst=True)

When using a metadata-level ENUM type, the type will always be created and dropped if either the metadata-wide create/drop is called:

metadata.create_all(engine)  # will emit CREATE TYPE
metadata.drop_all(engine)  # will emit DROP TYPE

The type can also be created and dropped directly:

my_enum.create(engine)
my_enum.drop(engine)

Changed in version 1.0.0: The PostgreSQL ENUM type now behaves more strictly with regards to CREATE/DROP. A metadata-level ENUM type will only be created and dropped at the metadata level, not the table level, with the exception of table.create(checkfirst=True). The table.drop() call will now emit a DROP TYPE for a table-level enumerated type.

Class signature

class sqlalchemy.dialects.postgresql.ENUM (sqlalchemy.types.NativeForEmulated, sqlalchemy.types.Enum)

method sqlalchemy.dialects.postgresql.ENUM.__init__(*enums, **kw)

Construct an ENUM.

Arguments are the same as that of Enum, but also including the following parameters.

Parameters:

create_type – Defaults to True. Indicates that CREATE TYPE should be emitted, after optionally checking for the presence of the type, when the parent table is being created; and additionally that DROP TYPE is called when the table is dropped. When False, no check will be performed and no CREATE TYPE or DROP TYPE is emitted, unless ENUM.create() or ENUM.drop() are called directly. Setting to False is helpful when invoking a creation scheme to a SQL file without access to the actual database - the ENUM.create() and ENUM.drop() methods can be used to emit SQL to a target bind.

method sqlalchemy.dialects.postgresql.ENUM.create(bind=None, checkfirst=True)

Emit CREATE TYPE for this ENUM.

If the underlying dialect does not support PostgreSQL CREATE TYPE, no action is taken.

Parameters:
  • bind – a connectable Engine, Connection, or similar object to emit SQL.

  • checkfirst – if True, a query against the PG catalog will be first performed to see if the type does not exist already before creating.

method sqlalchemy.dialects.postgresql.ENUM.drop(bind=None, checkfirst=True)

Emit DROP TYPE for this ENUM.

If the underlying dialect does not support PostgreSQL DROP TYPE, no action is taken.

Parameters:
  • bind – a connectable Engine, Connection, or similar object to emit SQL.

  • checkfirst – if True, a query against the PG catalog will be first performed to see if the type actually exists before dropping.

class sqlalchemy.dialects.postgresql.HSTORE(text_type=None)

Represent the PostgreSQL HSTORE type.

The HSTORE type stores dictionaries containing strings, e.g.:

data_table = Table('data_table', metadata,
    Column('id', Integer, primary_key=True),
    Column('data', HSTORE)
)

with engine.connect() as conn:
    conn.execute(
        data_table.insert(),
        data = {"key1": "value1", "key2": "value2"}
    )

HSTORE provides for a wide range of operations, including:

  • Index operations:

    data_table.c.data['some key'] == 'some value'
  • Containment operations:

    data_table.c.data.has_key('some key')
    
    data_table.c.data.has_all(['one', 'two', 'three'])
  • Concatenation:

    data_table.c.data + {"k1": "v1"}

For a full list of special methods see comparator_factory.

Detecting Changes in HSTORE columns when using the ORM

For usage with the SQLAlchemy ORM, it may be desirable to combine the usage of HSTORE with MutableDict dictionary now part of the sqlalchemy.ext.mutable extension. This extension will allow “in-place” changes to the dictionary, e.g. addition of new keys or replacement/removal of existing keys to/from the current dictionary, to produce events which will be detected by the unit of work:

from sqlalchemy.ext.mutable import MutableDict

class MyClass(Base):
    __tablename__ = 'data_table'

    id = Column(Integer, primary_key=True)
    data = Column(MutableDict.as_mutable(HSTORE))

my_object = session.query(MyClass).one()

# in-place mutation, requires Mutable extension
# in order for the ORM to detect
my_object.data['some_key'] = 'some value'

session.commit()

When the sqlalchemy.ext.mutable extension is not used, the ORM will not be alerted to any changes to the contents of an existing dictionary, unless that dictionary value is re-assigned to the HSTORE-attribute itself, thus generating a change event.

See also

hstore - render the PostgreSQL hstore() function.

class Comparator(expr)

Define comparison operations for HSTORE.

Class signature

class sqlalchemy.dialects.postgresql.HSTORE.Comparator (sqlalchemy.types.Comparator, sqlalchemy.types.Comparator)

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.array()

Text array expression. Returns array of alternating keys and values.

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.contained_by(other)

Boolean expression. Test if keys are a proper subset of the keys of the argument jsonb expression.

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.contains(other, **kwargs)

Boolean expression. Test if keys (or array) are a superset of/contained the keys of the argument jsonb expression.

kwargs may be ignored by this operator but are required for API conformance.

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.defined(key)

Boolean expression. Test for presence of a non-NULL value for the key. Note that the key may be a SQLA expression.

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.delete(key)

HStore expression. Returns the contents of this hstore with the given key deleted. Note that the key may be a SQLA expression.

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.has_all(other)

Boolean expression. Test for presence of all keys in jsonb

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.has_any(other)

Boolean expression. Test for presence of any key in jsonb

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.has_key(other)

Boolean expression. Test for presence of a key. Note that the key may be a SQLA expression.

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.keys()

Text array expression. Returns array of keys.

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.matrix()

Text array expression. Returns array of [key, value] pairs.

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.slice(array)

HStore expression. Returns a subset of an hstore defined by array of keys.

method sqlalchemy.dialects.postgresql.HSTORE.Comparator.vals()

Text array expression. Returns array of values.

method sqlalchemy.dialects.postgresql.HSTORE.__init__(text_type=None)

Construct a new HSTORE.

Parameters:

text_type

the type that should be used for indexed values. Defaults to Text.

New in version 1.1.0.

method sqlalchemy.dialects.postgresql.HSTORE.bind_processor(dialect)

Return a conversion function for processing bind values.

Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

If processing is not necessary, the method should return None.

Note

This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a TypeEngine class in order to provide an alternate TypeEngine.bind_processor() method, unless subclassing the UserDefinedType class explicitly.

To provide alternate behavior for TypeEngine.bind_processor(), implement a TypeDecorator class and provide an implementation of TypeDecorator.process_bind_param().

Parameters:

dialect – Dialect instance in use.

attribute sqlalchemy.dialects.postgresql.HSTORE.comparator_factory

alias of Comparator

attribute sqlalchemy.dialects.postgresql.HSTORE.hashable = False

Flag, if False, means values from this type aren’t hashable.

Used by the ORM when uniquing result lists.

method sqlalchemy.dialects.postgresql.HSTORE.result_processor(dialect, coltype)

Return a conversion function for processing result row values.

Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

If processing is not necessary, the method should return None.

Note

This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a TypeEngine class in order to provide an alternate TypeEngine.result_processor() method, unless subclassing the UserDefinedType class explicitly.

To provide alternate behavior for TypeEngine.result_processor(), implement a TypeDecorator class and provide an implementation of TypeDecorator.process_result_value().

Parameters:
  • dialect – Dialect instance in use.

  • coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.dialects.postgresql.hstore(*args, **kwargs)

Construct an hstore value within a SQL expression using the PostgreSQL hstore() function.

The hstore function accepts one or two arguments as described in the PostgreSQL documentation.

E.g.:

from sqlalchemy.dialects.postgresql import array, hstore

select(hstore('key1', 'value1'))

select(
    hstore(
        array(['key1', 'key2', 'key3']),
        array(['value1', 'value2', 'value3'])
    )
)

See also

HSTORE - the PostgreSQL HSTORE datatype.

Members

inherit_cache, type

attribute sqlalchemy.dialects.postgresql.hstore.inherit_cache = True

Indicate if this HasCacheKey instance should make use of the cache key generation scheme used by its immediate superclass.

The attribute defaults to None, which indicates that a construct has not yet taken into account whether or not its appropriate for it to participate in caching; this is functionally equivalent to setting the value to False, except that a warning is also emitted.

This flag can be set to True on a particular class, if the SQL that corresponds to the object does not change based on attributes which are local to this class, and not its superclass.

See also

Enabling Caching Support for Custom Constructs - General guideslines for setting the HasCacheKey.inherit_cache attribute for third-party or user defined SQL constructs.

attribute sqlalchemy.dialects.postgresql.hstore.type

alias of HSTORE

class sqlalchemy.dialects.postgresql.INET
class sqlalchemy.dialects.postgresql.INTERVAL(precision=None, fields=None)

PostgreSQL INTERVAL type.

Members

__init__()

Class signature

class sqlalchemy.dialects.postgresql.INTERVAL (sqlalchemy.types.NativeForEmulated, sqlalchemy.types._AbstractInterval)

method sqlalchemy.dialects.postgresql.INTERVAL.__init__(precision=None, fields=None)

Construct an INTERVAL.

Parameters:
  • precision – optional integer precision value

  • fields

    string fields specifier. allows storage of fields to be limited, such as "YEAR", "MONTH", "DAY TO HOUR", etc.

    New in version 1.2.

class sqlalchemy.dialects.postgresql.JSON(none_as_null=False, astext_type=None)

Represent the PostgreSQL JSON type.

JSON is used automatically whenever the base JSON datatype is used against a PostgreSQL backend, however base JSON datatype does not provide Python accessors for PostgreSQL-specific comparison methods such as Comparator.astext(); additionally, to use PostgreSQL JSONB, the JSONB datatype should be used explicitly.

See also

JSON - main documentation for the generic cross-platform JSON datatype.

The operators provided by the PostgreSQL version of JSON include:

  • Index operations (the -> operator):

    data_table.c.data['some key']
    
    data_table.c.data[5]
  • Index operations returning text (the ->> operator):

    data_table.c.data['some key'].astext == 'some value'

    Note that equivalent functionality is available via the Comparator.as_string accessor.

  • Index operations with CAST (equivalent to CAST(col ->> ['some key'] AS <type>)):

    data_table.c.data['some key'].astext.cast(Integer) == 5

    Note that equivalent functionality is available via the Comparator.as_integer and similar accessors.

  • Path index operations (the #> operator):

    data_table.c.data[('key_1', 'key_2', 5, ..., 'key_n')]
  • Path index operations returning text (the #>> operator):

    data_table.c.data[('key_1', 'key_2', 5, ..., 'key_n')].astext == 'some value'

Changed in version 1.1: The ColumnElement.cast() operator on JSON objects now requires that the Comparator.astext modifier be called explicitly, if the cast works only from a textual string.

Index operations return an expression object whose type defaults to JSON by default, so that further JSON-oriented instructions may be called upon the result type.

Custom serializers and deserializers are specified at the dialect level, that is using create_engine(). The reason for this is that when using psycopg2, the DBAPI only allows serializers at the per-cursor or per-connection level. E.g.:

engine = create_engine("postgresql://scott:tiger@localhost/test",
                        json_serializer=my_serialize_fn,
                        json_deserializer=my_deserialize_fn
                )

When using the psycopg2 dialect, the json_deserializer is registered against the database using psycopg2.extras.register_default_json.

See also

JSON - Core level JSON type

JSONB

Changed in version 1.1: JSON is now a PostgreSQL- specific specialization of the new JSON type.

class Comparator(expr)

Define comparison operations for JSON.

Class signature

class sqlalchemy.dialects.postgresql.JSON.Comparator (sqlalchemy.types.Comparator)

attribute sqlalchemy.dialects.postgresql.JSON.Comparator.astext

On an indexed expression, use the “astext” (e.g. “->>”) conversion when rendered in SQL.

E.g.:

select(data_table.c.data['some key'].astext)
method sqlalchemy.dialects.postgresql.JSON.__init__(none_as_null=False, astext_type=None)

Construct a JSON type.

Parameters:
  • none_as_null

    if True, persist the value None as a SQL NULL value, not the JSON encoding of null. Note that when this flag is False, the null() construct can still be used to persist a NULL value:

    from sqlalchemy import null
    conn.execute(table.insert(), data=null())

    Changed in version 0.9.8: - Added none_as_null, and null() is now supported in order to persist a NULL value.

    See also

    JSON.NULL

  • astext_type

    the type to use for the Comparator.astext accessor on indexed attributes. Defaults to Text.

    New in version 1.1.

attribute sqlalchemy.dialects.postgresql.JSON.comparator_factory

alias of Comparator

class sqlalchemy.dialects.postgresql.JSONB(none_as_null=False, astext_type=None)

Represent the PostgreSQL JSONB type.

The JSONB type stores arbitrary JSONB format data, e.g.:

data_table = Table('data_table', metadata,
    Column('id', Integer, primary_key=True),
    Column('data', JSONB)
)

with engine.connect() as conn:
    conn.execute(
        data_table.insert(),
        data = {"key1": "value1", "key2": "value2"}
    )

The JSONB type includes all operations provided by JSON, including the same behaviors for indexing operations. It also adds additional operators specific to JSONB, including Comparator.has_key(), Comparator.has_all(), Comparator.has_any(), Comparator.contains(), and Comparator.contained_by().

Like the JSON type, the JSONB type does not detect in-place changes when used with the ORM, unless the sqlalchemy.ext.mutable extension is used.

Custom serializers and deserializers are shared with the JSON class, using the json_serializer and json_deserializer keyword arguments. These must be specified at the dialect level using create_engine(). When using psycopg2, the serializers are associated with the jsonb type using psycopg2.extras.register_default_jsonb on a per-connection basis, in the same way that psycopg2.extras.register_default_json is used to register these handlers with the json type.

New in version 0.9.7.

See also

JSON

class Comparator(expr)

Define comparison operations for JSON.

Class signature

class sqlalchemy.dialects.postgresql.JSONB.Comparator (sqlalchemy.dialects.postgresql.json.Comparator)

method sqlalchemy.dialects.postgresql.JSONB.Comparator.contained_by(other)

Boolean expression. Test if keys are a proper subset of the keys of the argument jsonb expression (equivalent of the <@ operator).

method sqlalchemy.dialects.postgresql.JSONB.Comparator.contains(other, **kwargs)

Boolean expression. Test if keys (or array) are a superset of/contained the keys of the argument jsonb expression (equivalent of the @> operator).

kwargs may be ignored by this operator but are required for API conformance.

method sqlalchemy.dialects.postgresql.JSONB.Comparator.has_all(other)

Boolean expression. Test for presence of all keys in jsonb (equivalent of the ?& operator)

method sqlalchemy.dialects.postgresql.JSONB.Comparator.has_any(other)

Boolean expression. Test for presence of any key in jsonb (equivalent of the ?| operator)

method sqlalchemy.dialects.postgresql.JSONB.Comparator.has_key(other)

Boolean expression. Test for presence of a key (equivalent of the ? operator). Note that the key may be a SQLA expression.

attribute sqlalchemy.dialects.postgresql.JSONB.comparator_factory

alias of Comparator

class sqlalchemy.dialects.postgresql.MACADDR
class sqlalchemy.dialects.postgresql.MACADDR8
class sqlalchemy.dialects.postgresql.MONEY

Provide the PostgreSQL MONEY type.

Depending on driver, result rows using this type may return a string value which includes currency symbols.

For this reason, it may be preferable to provide conversion to a numerically-based currency datatype using TypeDecorator:

import re
import decimal
from sqlalchemy import TypeDecorator

class NumericMoney(TypeDecorator):
    impl = MONEY

    def process_result_value(self, value: Any, dialect: Any) -> None:
        if value is not None:
            # adjust this for the currency and numeric
            m = re.match(r"\$([\d.]+)", value)
            if m:
                value = decimal.Decimal(m.group(1))
        return value

Alternatively, the conversion may be applied as a CAST using the TypeDecorator.column_expression() method as follows:

import decimal
from sqlalchemy import cast
from sqlalchemy import TypeDecorator

class NumericMoney(TypeDecorator):
    impl = MONEY

    def column_expression(self, column: Any):
        return cast(column, Numeric())

New in version 1.2.

class sqlalchemy.dialects.postgresql.OID

Provide the PostgreSQL OID type.

New in version 0.9.5.

class sqlalchemy.dialects.postgresql.REAL(precision=None, asdecimal=False, decimal_return_scale=None)

The SQL REAL type.

Class signature

class sqlalchemy.dialects.postgresql.REAL (sqlalchemy.types.Float)

method sqlalchemy.dialects.postgresql.REAL.__init__(precision=None, asdecimal=False, decimal_return_scale=None)

inherited from the sqlalchemy.types.Float.__init__ method of Float

Construct a Float.

Parameters:
  • precision – the numeric precision for use in DDL CREATE TABLE.

  • asdecimal – the same flag as that of Numeric, but defaults to False. Note that setting this flag to True results in floating point conversion.

  • decimal_return_scale

    Default scale to use when converting from floats to Python decimals. Floating point values will typically be much longer due to decimal inaccuracy, and most floating point database types don’t have a notion of “scale”, so by default the float type looks for the first ten decimal places when converting. Specifying this value will override that length. Note that the MySQL float types, which do include “scale”, will use “scale” as the default for decimal_return_scale, if not otherwise specified.

    New in version 0.9.0.

class sqlalchemy.dialects.postgresql.REGCLASS

Provide the PostgreSQL REGCLASS type.

New in version 1.2.7.

class sqlalchemy.dialects.postgresql.TIMESTAMP(timezone=False, precision=None)

Provide the PostgreSQL TIMESTAMP type.

Members

__init__()

method sqlalchemy.dialects.postgresql.TIMESTAMP.__init__(timezone=False, precision=None)

Construct a TIMESTAMP.

Parameters:
  • timezone – boolean value if timezone present, default False

  • precision

    optional integer precision value

    New in version 1.4.

class sqlalchemy.dialects.postgresql.TIME(timezone=False, precision=None)

PostgreSQL TIME type.

Members

__init__()

method sqlalchemy.dialects.postgresql.TIME.__init__(timezone=False, precision=None)

Construct a TIME.

Parameters:
  • timezone – boolean value if timezone present, default False

  • precision

    optional integer precision value

    New in version 1.4.

class sqlalchemy.dialects.postgresql.TSVECTOR

The TSVECTOR type implements the PostgreSQL text search type TSVECTOR.

It can be used to do full text queries on natural language documents.

New in version 0.9.0.

See also

Full Text Search

class sqlalchemy.dialects.postgresql.UUID(as_uuid=False)

PostgreSQL UUID type.

Represents the UUID column type, interpreting data either as natively returned by the DBAPI or as Python uuid objects.

The UUID type is currently known to work within the prominent DBAPI drivers supported by SQLAlchemy including psycopg2, pg8000 and asyncpg. Support for other DBAPI drivers may be incomplete or non-present.

Members

__init__()

method sqlalchemy.dialects.postgresql.UUID.__init__(as_uuid=False)

Construct a UUID type.

Parameters:

as_uuid=False – if True, values will be interpreted as Python uuid objects, converting to/from string via the DBAPI.

Range Types

The new range column types found in PostgreSQL 9.2 onwards are catered for by the following types:

Object Name Description

DATERANGE

Represent the PostgreSQL DATERANGE type.

INT4RANGE

Represent the PostgreSQL INT4RANGE type.

INT8RANGE

Represent the PostgreSQL INT8RANGE type.

NUMRANGE

Represent the PostgreSQL NUMRANGE type.

RangeOperators

This mixin provides functionality for the Range Operators listed in the Range Operators table of the PostgreSQL documentation for Range Functions and Operators. It is used by all the range types provided in the postgres dialect and can likely be used for any range types you create yourself.

TSRANGE

Represent the PostgreSQL TSRANGE type.

TSTZRANGE

Represent the PostgreSQL TSTZRANGE type.

class sqlalchemy.dialects.postgresql.INT4RANGE

Represent the PostgreSQL INT4RANGE type.

class sqlalchemy.dialects.postgresql.INT8RANGE

Represent the PostgreSQL INT8RANGE type.

class sqlalchemy.dialects.postgresql.NUMRANGE

Represent the PostgreSQL NUMRANGE type.

class sqlalchemy.dialects.postgresql.DATERANGE

Represent the PostgreSQL DATERANGE type.

class sqlalchemy.dialects.postgresql.TSRANGE

Represent the PostgreSQL TSRANGE type.

class sqlalchemy.dialects.postgresql.TSTZRANGE

Represent the PostgreSQL TSTZRANGE type.

The types above get most of their functionality from the following mixin:

class sqlalchemy.dialects.postgresql.ranges.RangeOperators

This mixin provides functionality for the Range Operators listed in the Range Operators table of the PostgreSQL documentation for Range Functions and Operators. It is used by all the range types provided in the postgres dialect and can likely be used for any range types you create yourself.

No extra support is provided for the Range Functions listed in the Range Functions table of the PostgreSQL documentation. For these, the normal func() object should be used.

class comparator_factory(expr)

Define comparison operations for range types.

Class signature

class sqlalchemy.dialects.postgresql.ranges.RangeOperators.comparator_factory (sqlalchemy.types.Comparator)

method sqlalchemy.dialects.postgresql.ranges.RangeOperators.comparator_factory.__ne__(other)

Boolean expression. Returns true if two ranges are not equal

method sqlalchemy.dialects.postgresql.ranges.RangeOperators.comparator_factory.adjacent_to(other)

Boolean expression. Returns true if the range in the column is adjacent to the range in the operand.

method sqlalchemy.dialects.postgresql.ranges.RangeOperators.comparator_factory.contained_by(other)

Boolean expression. Returns true if the column is contained within the right hand operand.

method sqlalchemy.dialects.postgresql.ranges.RangeOperators.comparator_factory.contains(other, **kw)

Boolean expression. Returns true if the right hand operand, which can be an element or a range, is contained within the column.

kwargs may be ignored by this operator but are required for API conformance.

method sqlalchemy.dialects.postgresql.ranges.RangeOperators.comparator_factory.not_extend_left_of(other)

Boolean expression. Returns true if the range in the column does not extend left of the range in the operand.

method sqlalchemy.dialects.postgresql.ranges.RangeOperators.comparator_factory.not_extend_right_of(other)

Boolean expression. Returns true if the range in the column does not extend right of the range in the operand.

method sqlalchemy.dialects.postgresql.ranges.RangeOperators.comparator_factory.overlaps(other)

Boolean expression. Returns true if the column overlaps (has points in common with) the right hand operand.

method sqlalchemy.dialects.postgresql.ranges.RangeOperators.comparator_factory.strictly_left_of(other)

Boolean expression. Returns true if the column is strictly left of the right hand operand.

method sqlalchemy.dialects.postgresql.ranges.RangeOperators.comparator_factory.strictly_right_of(other)

Boolean expression. Returns true if the column is strictly right of the right hand operand.

Warning

The range type DDL support should work with any PostgreSQL DBAPI driver, however the data types returned may vary. If you are using psycopg2, it’s recommended to upgrade to version 2.5 or later before using these column types.

When instantiating models that use these column types, you should pass whatever data type is expected by the DBAPI driver you’re using for the column type. For psycopg2 these are psycopg2.extras.NumericRange, psycopg2.extras.DateRange, psycopg2.extras.DateTimeRange and psycopg2.extras.DateTimeTZRange or the class you’ve registered with psycopg2.extras.register_range.

For example:

from psycopg2.extras import DateTimeRange
from sqlalchemy.dialects.postgresql import TSRANGE

class RoomBooking(Base):

    __tablename__ = 'room_booking'

    room = Column(Integer(), primary_key=True)
    during = Column(TSRANGE())

booking = RoomBooking(
    room=101,
    during=DateTimeRange(datetime(2013, 3, 23), None)
)

PostgreSQL Constraint Types

SQLAlchemy supports PostgreSQL EXCLUDE constraints via the ExcludeConstraint class:

Object Name Description

ExcludeConstraint

A table-level EXCLUDE constraint.

class sqlalchemy.dialects.postgresql.ExcludeConstraint(*elements, **kw)

A table-level EXCLUDE constraint.

Defines an EXCLUDE constraint as described in the PostgreSQL documentation.

Members

__init__()

method sqlalchemy.dialects.postgresql.ExcludeConstraint.__init__(*elements, **kw)

Create an ExcludeConstraint object.

E.g.:

const = ExcludeConstraint(
    (Column('period'), '&&'),
    (Column('group'), '='),
    where=(Column('group') != 'some group'),
    ops={'group': 'my_operator_class'}
)

The constraint is normally embedded into the Table construct directly, or added later using append_constraint():

some_table = Table(
    'some_table', metadata,
    Column('id', Integer, primary_key=True),
    Column('period', TSRANGE()),
    Column('group', String)
)

some_table.append_constraint(
    ExcludeConstraint(
        (some_table.c.period, '&&'),
        (some_table.c.group, '='),
        where=some_table.c.group != 'some group',
        name='some_table_excl_const',
        ops={'group': 'my_operator_class'}
    )
)
Parameters:
  • *elements – A sequence of two tuples of the form (column, operator) where “column” is a SQL expression element or a raw SQL string, most typically a Column object, and “operator” is a string containing the operator to use. In order to specify a column name when a Column object is not available, while ensuring that any necessary quoting rules take effect, an ad-hoc Column or column() object should be used.

  • name – Optional, the in-database name of this constraint.

  • deferrable – Optional bool. If set, emit DEFERRABLE or NOT DEFERRABLE when issuing DDL for this constraint.

  • initially – Optional string. If set, emit INITIALLY <value> when issuing DDL for this constraint.

  • using – Optional string. If set, emit USING <index_method> when issuing DDL for this constraint. Defaults to ‘gist’.

  • where

    Optional SQL expression construct or literal SQL string. If set, emit WHERE <predicate> when issuing DDL for this constraint.

    Warning

    The ExcludeConstraint.where argument to ExcludeConstraint can be passed as a Python string argument, which will be treated as trusted SQL text and rendered as given. DO NOT PASS UNTRUSTED INPUT TO THIS PARAMETER.

  • ops

    Optional dictionary. Used to define operator classes for the elements; works the same way as that of the postgresql_ops parameter specified to the Index construct.

    New in version 1.3.21.

    See also

    Operator Classes - general description of how PostgreSQL operator classes are specified.

For example:

from sqlalchemy.dialects.postgresql import ExcludeConstraint, TSRANGE


class RoomBooking(Base):

    __tablename__ = "room_booking"

    room = Column(Integer(), primary_key=True)
    during = Column(TSRANGE())

    __table_args__ = (ExcludeConstraint(("room", "="), ("during", "&&")),)

PostgreSQL DML Constructs

Object Name Description

insert(table[, values, inline, bind, ...], **dialect_kw)

Construct an Insert object.

Insert

PostgreSQL-specific implementation of INSERT.

function sqlalchemy.dialects.postgresql.insert(table, values=None, inline=False, bind=None, prefixes=None, returning=None, return_defaults=False, **dialect_kw)

Construct an Insert object.

This documentation is inherited from sqlalchemy.sql.expression.insert(); this constructor, sqlalchemy.dialects.postgresql.insert(), creates a sqlalchemy.dialects.postgresql.Insert object. See that class for additional details describing this subclass.

E.g.:

from sqlalchemy import insert

stmt = (
    insert(user_table).
    values(name='username', fullname='Full Username')
)

Similar functionality is available via the TableClause.insert() method on Table.

Parameters:
  • tableTableClause which is the subject of the insert.

  • values

    collection of values to be inserted; see Insert.values() for a description of allowed formats here. Can be omitted entirely; a Insert construct will also dynamically render the VALUES clause at execution time based on the parameters passed to Connection.execute().

    Deprecated since version 1.4: The insert.values parameter will be removed in SQLAlchemy 2.0. Please refer to the Insert.values() method.

  • inline

    if True, no attempt will be made to retrieve the SQL-generated default values to be provided within the statement; in particular, this allows SQL expressions to be rendered ‘inline’ within the statement without the need to pre-execute them beforehand; for backends that support “returning”, this turns off the “implicit returning” feature for the statement.

    Deprecated since version 1.4: The insert.inline parameter will be removed in SQLAlchemy 2.0. Please use the Insert.inline() method.

If both Insert.values and compile-time bind parameters are present, the compile-time bind parameters override the information specified within Insert.values on a per-key basis.

The keys within Insert.values can be either Column objects or their string identifiers. Each key may reference one of:

  • a literal data value (i.e. string, number, etc.);

  • a Column object;

  • a SELECT statement.

If a SELECT statement is specified which references this INSERT statement’s table, the statement will be correlated against the INSERT statement.

class sqlalchemy.dialects.postgresql.Insert(table, values=None, inline=False, bind=None, prefixes=None, returning=None, return_defaults=False, **dialect_kw)

PostgreSQL-specific implementation of INSERT.

Adds methods for PG-specific syntaxes such as ON CONFLICT.

The Insert object is created using the sqlalchemy.dialects.postgresql.insert() function.

New in version 1.1.

attribute sqlalchemy.dialects.postgresql.Insert.excluded

Provide the excluded namespace for an ON CONFLICT statement

PG’s ON CONFLICT clause allows reference to the row that would be inserted, known as excluded. This attribute provides all columns in this row to be referenceable.

Tip

The Insert.excluded attribute is an instance of ColumnCollection, which provides an interface the same as that of the Table.c collection described at Accessing Tables and Columns. With this collection, ordinary names are accessible like attributes (e.g. stmt.excluded.some_column), but special names and dictionary method names should be accessed using indexed access, such as stmt.excluded["column name"] or stmt.excluded["values"]. See the docstring for ColumnCollection for further examples.

See also

INSERT…ON CONFLICT (Upsert) - example of how to use Insert.excluded

attribute sqlalchemy.dialects.postgresql.Insert.inherit_cache = False

Indicate if this HasCacheKey instance should make use of the cache key generation scheme used by its immediate superclass.

The attribute defaults to None, which indicates that a construct has not yet taken into account whether or not its appropriate for it to participate in caching; this is functionally equivalent to setting the value to False, except that a warning is also emitted.

This flag can be set to True on a particular class, if the SQL that corresponds to the object does not change based on attributes which are local to this class, and not its superclass.

See also

Enabling Caching Support for Custom Constructs - General guideslines for setting the HasCacheKey.inherit_cache attribute for third-party or user defined SQL constructs.

method sqlalchemy.dialects.postgresql.Insert.on_conflict_do_nothing(constraint=None, index_elements=None, index_where=None)

Specifies a DO NOTHING action for ON CONFLICT clause.

The constraint and index_elements arguments are optional, but only one of these can be specified.

Parameters:
  • constraint – The name of a unique or exclusion constraint on the table, or the constraint object itself if it has a .name attribute.

  • index_elements – A sequence consisting of string column names, Column objects, or other column expression objects that will be used to infer a target index.

  • index_where

    Additional WHERE criterion that can be used to infer a conditional target index.

    New in version 1.1.

method sqlalchemy.dialects.postgresql.Insert.on_conflict_do_update(constraint=None, index_elements=None, index_where=None, set_=None, where=None)

Specifies a DO UPDATE SET action for ON CONFLICT clause.

Either the constraint or index_elements argument is required, but only one of these can be specified.

Parameters:
  • constraint – The name of a unique or exclusion constraint on the table, or the constraint object itself if it has a .name attribute.

  • index_elements – A sequence consisting of string column names, Column objects, or other column expression objects that will be used to infer a target index.

  • index_where – Additional WHERE criterion that can be used to infer a conditional target index.

  • set_

    A dictionary or other mapping object where the keys are either names of columns in the target table, or Column objects or other ORM-mapped columns matching that of the target table, and expressions or literals as values, specifying the SET actions to take.

    New in version 1.4: The Insert.on_conflict_do_update.set_ parameter supports Column objects from the target Table as keys.

    Warning

    This dictionary does not take into account Python-specified default UPDATE values or generation functions, e.g. those specified using Column.onupdate. These values will not be exercised for an ON CONFLICT style of UPDATE, unless they are manually specified in the Insert.on_conflict_do_update.set_ dictionary.

  • where

    Optional argument. If present, can be a literal SQL string or an acceptable expression for a WHERE clause that restricts the rows affected by DO UPDATE SET. Rows not meeting the WHERE condition will not be updated (effectively a DO NOTHING for those rows).

    New in version 1.1.

psycopg2

Support for the PostgreSQL database via the psycopg2 driver.

DBAPI

Documentation and download information (if applicable) for psycopg2 is available at: https://pypi.org/project/psycopg2/

Connecting

Connect String:

postgresql+psycopg2://user:password@host:port/dbname[?key=value&key=value...]

psycopg2 Connect Arguments

Keyword arguments that are specific to the SQLAlchemy psycopg2 dialect may be passed to create_engine(), and include the following:

Tip

The above keyword arguments are dialect keyword arguments, meaning that they are passed as explicit keyword arguments to create_engine():

engine = create_engine(
    "postgresql+psycopg2://scott:tiger@localhost/test",
    isolation_level="SERIALIZABLE",
)

These should not be confused with DBAPI connect arguments, which are passed as part of the create_engine.connect_args dictionary and/or are passed in the URL query string, as detailed in the section Custom DBAPI connect() arguments / on-connect routines.

SSL Connections

The psycopg2 module has a connection argument named sslmode for controlling its behavior regarding secure (SSL) connections. The default is sslmode=prefer; it will attempt an SSL connection and if that fails it will fall back to an unencrypted connection. sslmode=require may be used to ensure that only secure connections are established. Consult the psycopg2 / libpq documentation for further options that are available.

Note that sslmode is specific to psycopg2 so it is included in the connection URI:

engine = sa.create_engine(
    "postgresql+psycopg2://scott:tiger@192.168.0.199:5432/test?sslmode=require"
)

Unix Domain Connections

psycopg2 supports connecting via Unix domain connections. When the host portion of the URL is omitted, SQLAlchemy passes None to psycopg2, which specifies Unix-domain communication rather than TCP/IP communication:

create_engine("postgresql+psycopg2://user:password@/dbname")

By default, the socket file used is to connect to a Unix-domain socket in /tmp, or whatever socket directory was specified when PostgreSQL was built. This value can be overridden by passing a pathname to psycopg2, using host as an additional keyword argument:

create_engine("postgresql+psycopg2://user:password@/dbname?host=/var/lib/postgresql")

Specifying multiple fallback hosts

psycopg2 supports multiple connection points in the connection string. When the host parameter is used multiple times in the query section of the URL, SQLAlchemy will create a single string of the host and port information provided to make the connections. Tokens may consist of host::port or just host; in the latter case, the default port is selected by libpq. In the example below, three host connections are specified, for HostA::PortA, HostB connecting to the default port, and HostC::PortC:

create_engine(
    "postgresql+psycopg2://user:password@/dbname?host=HostA:PortA&host=HostB&host=HostC:PortC"
)

As an alternative, libpq query string format also may be used; this specifies host and port as single query string arguments with comma-separated lists - the default port can be chosen by indicating an empty value in the comma separated list:

create_engine(
    "postgresql+psycopg2://user:password@/dbname?host=HostA,HostB,HostC&port=PortA,,PortC"
)

With either URL style, connections to each host is attempted based on a configurable strategy, which may be configured using the libpq target_session_attrs parameter. Per libpq this defaults to any which indicates a connection to each host is then attempted until a connection is successful. Other strategies include primary, prefer-standby, etc. The complete list is documented by PostgreSQL at libpq connection strings.

For example, to indicate two hosts using the primary strategy:

create_engine(
    "postgresql+psycopg2://user:password@/dbname?host=HostA:PortA&host=HostB&host=HostC:PortC&target_session_attrs=primary"
)

Changed in version 1.4.40: Port specification in psycopg2 multiple host format is repaired, previously ports were not correctly interpreted in this context. libpq comma-separated format is also now supported.

New in version 1.3.20: Support for multiple hosts in PostgreSQL connection string.

See also

libpq connection strings - please refer to this section in the libpq documentation for complete background on multiple host support.

Empty DSN Connections / Environment Variable Connections

The psycopg2 DBAPI can connect to PostgreSQL by passing an empty DSN to the libpq client library, which by default indicates to connect to a localhost PostgreSQL database that is open for “trust” connections. This behavior can be further tailored using a particular set of environment variables which are prefixed with PG_..., which are consumed by libpq to take the place of any or all elements of the connection string.

For this form, the URL can be passed without any elements other than the initial scheme:

engine = create_engine('postgresql+psycopg2://')

In the above form, a blank “dsn” string is passed to the psycopg2.connect() function which in turn represents an empty DSN passed to libpq.

New in version 1.3.2: support for parameter-less connections with psycopg2.

See also

Environment Variables - PostgreSQL documentation on how to use PG_... environment variables for connections.

Per-Statement/Connection Execution Options

The following DBAPI-specific options are respected when used with Connection.execution_options(), Executable.execution_options(), Query.execution_options(), in addition to those not specific to DBAPIs:

  • isolation_level - Set the transaction isolation level for the lifespan of a Connection (can only be set on a connection, not a statement or query). See Psycopg2 Transaction Isolation Level.

  • stream_results - Enable or disable usage of psycopg2 server side cursors - this feature makes use of “named” cursors in combination with special result handling methods so that result rows are not fully buffered. Defaults to False, meaning cursors are buffered by default.

  • max_row_buffer - when using stream_results, an integer value that specifies the maximum number of rows to buffer at a time. This is interpreted by the BufferedRowCursorResult, and if omitted the buffer will grow to ultimately store 1000 rows at a time.

    Changed in version 1.4: The max_row_buffer size can now be greater than 1000, and the buffer will grow to that size.

Psycopg2 Fast Execution Helpers

Modern versions of psycopg2 include a feature known as Fast Execution Helpers , which have been shown in benchmarking to improve psycopg2’s executemany() performance, primarily with INSERT statements, by multiple orders of magnitude. SQLAlchemy internally makes use of these extensions for executemany() style calls, which correspond to lists of parameters being passed to Connection.execute() as detailed in multiple parameter sets. The ORM also uses this mode internally whenever possible.

The two available extensions on the psycopg2 side are the execute_values() and execute_batch() functions. The psycopg2 dialect defaults to using the execute_values() extension for all qualifying INSERT statements.

Changed in version 1.4: The psycopg2 dialect now defaults to a new mode "values_only" for executemany_mode, which allows an order of magnitude performance improvement for INSERT statements, but does not include “batch” mode for UPDATE and DELETE statements which removes the ability of cursor.rowcount to function correctly.

The use of these extensions is controlled by the executemany_mode flag which may be passed to create_engine():

engine = create_engine(
    "postgresql+psycopg2://scott:tiger@host/dbname",
    executemany_mode='values_plus_batch')

Possible options for executemany_mode include:

  • values_only - this is the default value. the psycopg2 execute_values() extension is used for qualifying INSERT statements, which rewrites the INSERT to include multiple VALUES clauses so that many parameter sets can be inserted with one statement.

    New in version 1.4: Added "values_only" setting for executemany_mode which is also now the default.

  • None - No psycopg2 extensions are not used, and the usual cursor.executemany() method is used when invoking statements with multiple parameter sets.

  • 'batch' - Uses psycopg2.extras.execute_batch for all qualifying INSERT, UPDATE and DELETE statements, so that multiple copies of a SQL query, each one corresponding to a parameter set passed to executemany(), are joined into a single SQL string separated by a semicolon. When using this mode, the CursorResult.rowcount attribute will not contain a value for executemany-style executions.

  • 'values_plus_batch'- execute_values is used for qualifying INSERT statements, execute_batch is used for UPDATE and DELETE. When using this mode, the CursorResult.rowcount attribute will not contain a value for executemany-style executions against UPDATE and DELETE statements.

By “qualifying statements”, we mean that the statement being executed must be a Core insert(), update() or delete() construct, and not a plain textual SQL string or one constructed using text(). When using the ORM, all insert/update/delete statements used by the ORM flush process are qualifying.

The “page size” for the “values” and “batch” strategies can be affected by using the executemany_batch_page_size and executemany_values_page_size engine parameters. These control how many parameter sets should be represented in each execution. The “values” page size defaults to 1000, which is different that psycopg2’s default. The “batch” page size defaults to 100. These can be affected by passing new values to create_engine():

engine = create_engine(
    "postgresql+psycopg2://scott:tiger@host/dbname",
    executemany_mode='values',
    executemany_values_page_size=10000, executemany_batch_page_size=500)

Changed in version 1.4: The default for executemany_values_page_size is now 1000, up from 100.

See also

Sending Multiple Parameters - General information on using the Connection object to execute statements in such a way as to make use of the DBAPI .executemany() method.

Unicode with Psycopg2

The psycopg2 DBAPI driver supports Unicode data transparently. Under Python 2 only, the SQLAlchemy psycopg2 dialect will enable the psycopg2.extensions.UNICODE extension by default to ensure Unicode is handled properly; under Python 3, this is psycopg2’s default behavior.

The client character encoding can be controlled for the psycopg2 dialect in the following ways:

  • For PostgreSQL 9.1 and above, the client_encoding parameter may be passed in the database URL; this parameter is consumed by the underlying libpq PostgreSQL client library:

    engine = create_engine("postgresql+psycopg2://user:pass@host/dbname?client_encoding=utf8")

    Alternatively, the above client_encoding value may be passed using create_engine.connect_args for programmatic establishment with libpq:

    engine = create_engine(
        "postgresql+psycopg2://user:pass@host/dbname",
        connect_args={'client_encoding': 'utf8'}
    )
  • For all PostgreSQL versions, psycopg2 supports a client-side encoding value that will be passed to database connections when they are first established. The SQLAlchemy psycopg2 dialect supports this using the client_encoding parameter passed to create_engine():

    engine = create_engine(
        "postgresql+psycopg2://user:pass@host/dbname",
        client_encoding="utf8"
    )

    Tip

    The above client_encoding parameter admittedly is very similar in appearance to usage of the parameter within the create_engine.connect_args dictionary; the difference above is that the parameter is consumed by psycopg2 and is passed to the database connection using SET client_encoding TO 'utf8'; in the previously mentioned style, the parameter is instead passed through psycopg2 and consumed by the libpq library.

  • A common way to set up client encoding with PostgreSQL databases is to ensure it is configured within the server-side postgresql.conf file; this is the recommended way to set encoding for a server that is consistently of one encoding in all databases:

    # postgresql.conf file
    
    # client_encoding = sql_ascii # actually, defaults to database
                                 # encoding
    client_encoding = utf8

Disabling Native Unicode

Under Python 2 only, SQLAlchemy can also be instructed to skip the usage of the psycopg2 UNICODE extension and to instead utilize its own unicode encode/decode services, which are normally reserved only for those DBAPIs that don’t fully support unicode directly. Passing use_native_unicode=False to create_engine() will disable usage of psycopg2.extensions. UNICODE. SQLAlchemy will instead encode data itself into Python bytestrings on the way in and coerce from bytes on the way back, using the value of the create_engine() encoding parameter, which defaults to utf-8. SQLAlchemy’s own unicode encode/decode functionality is steadily becoming obsolete as most DBAPIs now support unicode fully.

Transactions

The psycopg2 dialect fully supports SAVEPOINT and two-phase commit operations.

Psycopg2 Transaction Isolation Level

As discussed in Transaction Isolation Level, all PostgreSQL dialects support setting of transaction isolation level both via the isolation_level parameter passed to create_engine() , as well as the isolation_level argument used by Connection.execution_options(). When using the psycopg2 dialect , these options make use of psycopg2’s set_isolation_level() connection method, rather than emitting a PostgreSQL directive; this is because psycopg2’s API-level setting is always emitted at the start of each transaction in any case.

The psycopg2 dialect supports these constants for isolation level:

  • READ COMMITTED

  • READ UNCOMMITTED

  • REPEATABLE READ

  • SERIALIZABLE

  • AUTOCOMMIT

NOTICE logging

The psycopg2 dialect will log PostgreSQL NOTICE messages via the sqlalchemy.dialects.postgresql logger. When this logger is set to the logging.INFO level, notice messages will be logged:

import logging

logging.getLogger('sqlalchemy.dialects.postgresql').setLevel(logging.INFO)

Above, it is assumed that logging is configured externally. If this is not the case, configuration such as logging.basicConfig() must be utilized:

import logging

logging.basicConfig()   # log messages to stdout
logging.getLogger('sqlalchemy.dialects.postgresql').setLevel(logging.INFO)

See also

Logging HOWTO - on the python.org website

HSTORE type

The psycopg2 DBAPI includes an extension to natively handle marshalling of the HSTORE type. The SQLAlchemy psycopg2 dialect will enable this extension by default when psycopg2 version 2.4 or greater is used, and it is detected that the target database has the HSTORE type set up for use. In other words, when the dialect makes the first connection, a sequence like the following is performed:

  1. Request the available HSTORE oids using psycopg2.extras.HstoreAdapter.get_oids(). If this function returns a list of HSTORE identifiers, we then determine that the HSTORE extension is present. This function is skipped if the version of psycopg2 installed is less than version 2.4.

  2. If the use_native_hstore flag is at its default of True, and we’ve detected that HSTORE oids are available, the psycopg2.extensions.register_hstore() extension is invoked for all connections.

The register_hstore() extension has the effect of all Python dictionaries being accepted as parameters regardless of the type of target column in SQL. The dictionaries are converted by this extension into a textual HSTORE expression. If this behavior is not desired, disable the use of the hstore extension by setting use_native_hstore to False as follows:

engine = create_engine("postgresql+psycopg2://scott:tiger@localhost/test",
            use_native_hstore=False)

The HSTORE type is still supported when the psycopg2.extensions.register_hstore() extension is not used. It merely means that the coercion between Python dictionaries and the HSTORE string format, on both the parameter side and the result side, will take place within SQLAlchemy’s own marshalling logic, and not that of psycopg2 which may be more performant.

pg8000

Support for the PostgreSQL database via the pg8000 driver.

DBAPI

Documentation and download information (if applicable) for pg8000 is available at: https://pypi.org/project/pg8000/

Connecting

Connect String:

postgresql+pg8000://user:password@host:port/dbname[?key=value&key=value...]

Changed in version 1.4: The pg8000 dialect has been updated for version 1.16.6 and higher, and is again part of SQLAlchemy’s continuous integration with full feature support.

Unicode

pg8000 will encode / decode string values between it and the server using the PostgreSQL client_encoding parameter; by default this is the value in the postgresql.conf file, which often defaults to SQL_ASCII. Typically, this can be changed to utf-8, as a more useful default:

#client_encoding = sql_ascii # actually, defaults to database
                             # encoding
client_encoding = utf8

The client_encoding can be overridden for a session by executing the SQL:

SET CLIENT_ENCODING TO ‘utf8’;

SQLAlchemy will execute this SQL on all new connections based on the value passed to create_engine() using the client_encoding parameter:

engine = create_engine(
    "postgresql+pg8000://user:pass@host/dbname", client_encoding='utf8')

SSL Connections

pg8000 accepts a Python SSLContext object which may be specified using the create_engine.connect_args dictionary:

import ssl
ssl_context = ssl.create_default_context()
engine = sa.create_engine(
    "postgresql+pg8000://scott:tiger@192.168.0.199/test",
    connect_args={"ssl_context": ssl_context},
)

If the server uses an automatically-generated certificate that is self-signed or does not match the host name (as seen from the client), it may also be necessary to disable hostname checking:

import ssl
ssl_context = ssl.create_default_context()
ssl_context.check_hostname = False
ssl_context.verify_mode = ssl.CERT_NONE
engine = sa.create_engine(
    "postgresql+pg8000://scott:tiger@192.168.0.199/test",
    connect_args={"ssl_context": ssl_context},
)

pg8000 Transaction Isolation Level

The pg8000 dialect offers the same isolation level settings as that of the psycopg2 dialect:

  • READ COMMITTED

  • READ UNCOMMITTED

  • REPEATABLE READ

  • SERIALIZABLE

  • AUTOCOMMIT

asyncpg

Support for the PostgreSQL database via the asyncpg driver.

DBAPI

Documentation and download information (if applicable) for asyncpg is available at: https://magicstack.github.io/asyncpg/

Connecting

Connect String:

postgresql+asyncpg://user:password@host:port/dbname[?key=value&key=value...]

The asyncpg dialect is SQLAlchemy’s first Python asyncio dialect.

Using a special asyncio mediation layer, the asyncpg dialect is usable as the backend for the SQLAlchemy asyncio extension package.

This dialect should normally be used only with the create_async_engine() engine creation function:

from sqlalchemy.ext.asyncio import create_async_engine
engine = create_async_engine("postgresql+asyncpg://user:pass@hostname/dbname")

The dialect can also be run as a “synchronous” dialect within the create_engine() function, which will pass “await” calls into an ad-hoc event loop. This mode of operation is of limited use and is for special testing scenarios only. The mode can be enabled by adding the SQLAlchemy-specific flag async_fallback to the URL in conjunction with create_engine():

# for testing purposes only; do not use in production!
engine = create_engine("postgresql+asyncpg://user:pass@hostname/dbname?async_fallback=true")

New in version 1.4.

Note

By default asyncpg does not decode the json and jsonb types and returns them as strings. SQLAlchemy sets default type decoder for json and jsonb types using the python builtin json.loads function. The json implementation used can be changed by setting the attribute json_deserializer when creating the engine with create_engine() or create_async_engine().

Prepared Statement Cache

The asyncpg SQLAlchemy dialect makes use of asyncpg.connection.prepare() for all statements. The prepared statement objects are cached after construction which appears to grant a 10% or more performance improvement for statement invocation. The cache is on a per-DBAPI connection basis, which means that the primary storage for prepared statements is within DBAPI connections pooled within the connection pool. The size of this cache defaults to 100 statements per DBAPI connection and may be adjusted using the prepared_statement_cache_size DBAPI argument (note that while this argument is implemented by SQLAlchemy, it is part of the DBAPI emulation portion of the asyncpg dialect, therefore is handled as a DBAPI argument, not a dialect argument):

engine = create_async_engine("postgresql+asyncpg://user:pass@hostname/dbname?prepared_statement_cache_size=500")

To disable the prepared statement cache, use a value of zero:

engine = create_async_engine("postgresql+asyncpg://user:pass@hostname/dbname?prepared_statement_cache_size=0")

New in version 1.4.0b2: Added prepared_statement_cache_size for asyncpg.

Warning

The asyncpg database driver necessarily uses caches for PostgreSQL type OIDs, which become stale when custom PostgreSQL datatypes such as ENUM objects are changed via DDL operations. Additionally, prepared statements themselves which are optionally cached by SQLAlchemy’s driver as described above may also become “stale” when DDL has been emitted to the PostgreSQL database which modifies the tables or other objects involved in a particular prepared statement.

The SQLAlchemy asyncpg dialect will invalidate these caches within its local process when statements that represent DDL are emitted on a local connection, but this is only controllable within a single Python process / database engine. If DDL changes are made from other database engines and/or processes, a running application may encounter asyncpg exceptions InvalidCachedStatementError and/or InternalServerError("cache lookup failed for type <oid>") if it refers to pooled database connections which operated upon the previous structures. The SQLAlchemy asyncpg dialect will recover from these error cases when the driver raises these exceptions by clearing its internal caches as well as those of the asyncpg driver in response to them, but cannot prevent them from being raised in the first place if the cached prepared statement or asyncpg type caches have gone stale, nor can it retry the statement as the PostgreSQL transaction is invalidated when these errors occur.

Disabling the PostgreSQL JIT to improve ENUM datatype handling

Asyncpg has an issue when using PostgreSQL ENUM datatypes, where upon the creation of new database connections, an expensive query may be emitted in order to retrieve metadata regarding custom types which has been shown to negatively affect performance. To mitigate this issue, the PostgreSQL “jit” setting may be disabled from the client using this setting passed to create_async_engine():

engine = create_async_engine(
    "postgresql+asyncpg://user:password@localhost/tmp",
    connect_args={"server_settings": {"jit": "off"}},
)

psycopg2cffi

Support for the PostgreSQL database via the psycopg2cffi driver.

DBAPI

Documentation and download information (if applicable) for psycopg2cffi is available at: https://pypi.org/project/psycopg2cffi/

Connecting

Connect String:

postgresql+psycopg2cffi://user:password@host:port/dbname[?key=value&key=value...]

psycopg2cffi is an adaptation of psycopg2, using CFFI for the C layer. This makes it suitable for use in e.g. PyPy. Documentation is as per psycopg2.

New in version 1.0.0.

py-postgresql

Support for the PostgreSQL database via the py-postgresql driver.

DBAPI

Documentation and download information (if applicable) for py-postgresql is available at: https://python.projects.pgfoundry.org/

Connecting

Connect String:

postgresql+pypostgresql://user:password@host:port/dbname[?key=value&key=value...]

Note

The pypostgresql dialect is not tested as part of SQLAlchemy’s continuous integration and may have unresolved issues. The recommended PostgreSQL driver is psycopg2.

Deprecated since version 1.4: The py-postgresql DBAPI is deprecated and will be removed in a future version. This DBAPI is superseded by the external version available at external-dialect. Please use the external version or one of the supported DBAPIs to connect to PostgreSQL.

pygresql

Support for the PostgreSQL database via the pygresql driver.

DBAPI

Documentation and download information (if applicable) for pygresql is available at: https://www.pygresql.org/

Connecting

Connect String:

postgresql+pygresql://user:password@host:port/dbname[?key=value&key=value...]

Note

The pygresql dialect is not tested as part of SQLAlchemy’s continuous integration and may have unresolved issues. The recommended PostgreSQL dialect is psycopg2.

Deprecated since version 1.4: The pygresql DBAPI is deprecated and will be removed in a future version. Please use one of the supported DBAPIs to connect to PostgreSQL.