SQLAlchemy 1.4 Documentation
SQLAlchemy ORM
- ORM Quick Start
- Object Relational Tutorial (1.x API)
- ORM Mapped Class Configuration
- Relationship Configuration
- Querying Data, Loading Objects
- ORM Querying Guide
- Loading Columns
- Relationship Loading Techniques
- Loading Inheritance Hierarchies
- Query API¶
- The Query Object
Query
Query.__init__()
Query.add_column()
Query.add_columns()
Query.add_entity()
Query.all()
Query.apply_labels()
Query.as_scalar()
Query.autoflush()
Query.bind
Query.column_descriptions
Query.correlate()
Query.count()
Query.cte()
Query.delete()
Query.distinct()
Query.enable_assertions()
Query.enable_eagerloads()
Query.except_()
Query.except_all()
Query.execute()
Query.execution_options()
Query.exists()
Query.filter()
Query.filter_by()
Query.first()
Query.from_self()
Query.from_statement()
Query.get()
Query.get_execution_options()
Query.get_label_style
Query.group_by()
Query.having()
Query.instances()
Query.intersect()
Query.intersect_all()
Query.is_single_entity
Query.join()
Query.label()
Query.lazy_loaded_from
Query.limit()
Query.memoized_instancemethod()
Query.merge_result()
Query.offset()
Query.one()
Query.one_or_none()
Query.only_return_tuples()
Query.options()
Query.order_by()
Query.outerjoin()
Query.params()
Query.populate_existing()
Query.prefix_with()
Query.reset_joinpoint()
Query.scalar()
Query.scalar_subquery()
Query.select_entity_from()
Query.select_from()
Query.selectable
Query.set_label_style()
Query.slice()
Query.statement
Query.subquery()
Query.suffix_with()
Query.union()
Query.union_all()
Query.update()
Query.value()
Query.values()
Query.where()
Query.whereclause
Query.with_entities()
Query.with_for_update()
Query.with_hint()
Query.with_labels()
Query.with_parent()
Query.with_polymorphic()
Query.with_session()
Query.with_statement_hint()
Query.with_transformation()
Query.yield_per()
- ORM-Specific Query Constructs
- The Query Object
- Using the Session
- Events and Internals
- ORM Extensions
- ORM Examples
Project Versions
- Previous: Loading Inheritance Hierarchies
- Next: Using the Session
- Up: Home
- On this page:
- Query API
- The Query Object
Query
Query.__init__()
Query.add_column()
Query.add_columns()
Query.add_entity()
Query.all()
Query.apply_labels()
Query.as_scalar()
Query.autoflush()
Query.bind
Query.column_descriptions
Query.correlate()
Query.count()
Query.cte()
Query.delete()
Query.distinct()
Query.enable_assertions()
Query.enable_eagerloads()
Query.except_()
Query.except_all()
Query.execute()
Query.execution_options()
Query.exists()
Query.filter()
Query.filter_by()
Query.first()
Query.from_self()
Query.from_statement()
Query.get()
Query.get_execution_options()
Query.get_label_style
Query.group_by()
Query.having()
Query.instances()
Query.intersect()
Query.intersect_all()
Query.is_single_entity
Query.join()
Query.label()
Query.lazy_loaded_from
Query.limit()
Query.memoized_instancemethod()
Query.merge_result()
Query.offset()
Query.one()
Query.one_or_none()
Query.only_return_tuples()
Query.options()
Query.order_by()
Query.outerjoin()
Query.params()
Query.populate_existing()
Query.prefix_with()
Query.reset_joinpoint()
Query.scalar()
Query.scalar_subquery()
Query.select_entity_from()
Query.select_from()
Query.selectable
Query.set_label_style()
Query.slice()
Query.statement
Query.subquery()
Query.suffix_with()
Query.union()
Query.union_all()
Query.update()
Query.value()
Query.values()
Query.where()
Query.whereclause
Query.with_entities()
Query.with_for_update()
Query.with_hint()
Query.with_labels()
Query.with_parent()
Query.with_polymorphic()
Query.with_session()
Query.with_statement_hint()
Query.with_transformation()
Query.yield_per()
- ORM-Specific Query Constructs
- The Query Object
Query API¶
This section presents the API reference for the ORM Query
object. For a walkthrough
of how to use this object, see Object Relational Tutorial (1.x API).
The Query Object¶
Query
is produced in terms of a given Session
, using the Session.query()
method:
q = session.query(SomeMappedClass)
Following is the full interface for the Query
object.
Object Name | Description |
---|---|
ORM-level SQL construction object. |
- class sqlalchemy.orm.Query(entities, session=None)¶
ORM-level SQL construction object.
Query
is the source of all SELECT statements generated by the ORM, both those formulated by end-user query operations as well as by high level internal operations such as related collection loading. It features a generative interface whereby successive calls return a newQuery
object, a copy of the former with additional criteria and options associated with it.Query
objects are normally initially generated using theSession.query()
method ofSession
, and in less common cases by instantiating theQuery
directly and associating with aSession
using theQuery.with_session()
method.For a full walk through of
Query
usage, see the Object Relational Tutorial (1.x API).Members
__init__(), add_column(), add_columns(), add_entity(), all(), apply_labels(), as_scalar(), autoflush(), bind, column_descriptions, correlate(), count(), cte(), delete(), distinct(), enable_assertions(), enable_eagerloads(), except_(), except_all(), execute(), execution_options(), exists(), filter(), filter_by(), first(), from_self(), from_statement(), get(), get_execution_options(), get_label_style, group_by(), having(), instances(), intersect(), intersect_all(), is_single_entity, join(), label(), lazy_loaded_from, limit(), memoized_instancemethod(), merge_result(), offset(), one(), one_or_none(), only_return_tuples(), options(), order_by(), outerjoin(), params(), populate_existing(), prefix_with(), reset_joinpoint(), scalar(), scalar_subquery(), select_entity_from(), select_from(), selectable, set_label_style(), slice(), statement, subquery(), suffix_with(), union(), union_all(), update(), value(), values(), where(), whereclause, with_entities(), with_for_update(), with_hint(), with_labels(), with_parent(), with_polymorphic(), with_session(), with_statement_hint(), with_transformation(), yield_per()
Class signature
class
sqlalchemy.orm.Query
(sqlalchemy.sql.expression._SelectFromElements
,sqlalchemy.sql.annotation.SupportsCloneAnnotations
,sqlalchemy.sql.expression.HasPrefixes
,sqlalchemy.sql.expression.HasSuffixes
,sqlalchemy.sql.expression.HasHints
,sqlalchemy.sql.expression.Executable
)-
method
sqlalchemy.orm.Query.
__init__(entities, session=None)¶ Construct a
Query
directly.E.g.:
q = Query([User, Address], session=some_session)
The above is equivalent to:
q = some_session.query(User, Address)
-
method
sqlalchemy.orm.Query.
add_column(column)¶ Add a column expression to the list of result columns to be returned.
Deprecated since version 1.4:
Query.add_column()
is deprecated and will be removed in a future release. Please useQuery.add_columns()
-
method
sqlalchemy.orm.Query.
add_columns(*column)¶ Add one or more column expressions to the list of result columns to be returned.
-
method
sqlalchemy.orm.Query.
add_entity(entity, alias=None)¶ add a mapped entity to the list of result columns to be returned.
-
method
sqlalchemy.orm.Query.
all()¶ Return the results represented by this
Query
as a list.This results in an execution of the underlying SQL statement.
Warning
The
Query
object, when asked to return either a sequence or iterator that consists of full ORM-mapped entities, will deduplicate entries based on primary key. See the FAQ for more details.
-
method
sqlalchemy.orm.Query.
apply_labels()¶ Deprecated since version 1.4: The
Query.with_labels()
andQuery.apply_labels()
method is considered legacy as of the 1.x series of SQLAlchemy and will be removed in 2.0. Use set_label_style(LABEL_STYLE_TABLENAME_PLUS_COL) instead. (Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)
-
method
sqlalchemy.orm.Query.
as_scalar()¶ Return the full SELECT statement represented by this
Query
, converted to a scalar subquery.Deprecated since version 1.4: The
Query.as_scalar()
method is deprecated and will be removed in a future release. Please refer toQuery.scalar_subquery()
.
-
method
sqlalchemy.orm.Query.
autoflush(setting)¶ Return a Query with a specific ‘autoflush’ setting.
As of SQLAlchemy 1.4, the
Query.autoflush()
method is equivalent to using theautoflush
execution option at the ORM level. See the section Autoflush for further background on this option.
-
attribute
sqlalchemy.orm.Query.
bind¶ inherited from the
Executable.bind
attribute ofExecutable
Returns the
Engine
orConnection
to which thisExecutable
is bound, or None if none found.Deprecated since version 1.4: The
Executable.bind
attribute is considered legacy as of the 1.x series of SQLAlchemy and will be removed in 2.0. Bound metadata is being removed as of SQLAlchemy 2.0. (Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)This is a traversal which checks locally, then checks among the “from” clauses of associated objects until a bound engine or connection is found.
-
attribute
sqlalchemy.orm.Query.
column_descriptions¶ Return metadata about the columns which would be returned by this
Query
.Format is a list of dictionaries:
user_alias = aliased(User, name='user2') q = sess.query(User, User.id, user_alias) # this expression: q.column_descriptions # would return: [ { 'name':'User', 'type':User, 'aliased':False, 'expr':User, 'entity': User }, { 'name':'id', 'type':Integer(), 'aliased':False, 'expr':User.id, 'entity': User }, { 'name':'user2', 'type':User, 'aliased':True, 'expr':user_alias, 'entity': user_alias } ]
See also
This API is available using 2.0 style queries as well, documented at:
-
method
sqlalchemy.orm.Query.
correlate(*fromclauses)¶ Return a
Query
construct which will correlate the given FROM clauses to that of an enclosingQuery
orselect()
.The method here accepts mapped classes,
aliased()
constructs, andmapper()
constructs as arguments, which are resolved into expression constructs, in addition to appropriate expression constructs.The correlation arguments are ultimately passed to
Select.correlate()
after coercion to expression constructs.The correlation arguments take effect in such cases as when
Query.from_self()
is used, or when a subquery as returned byQuery.subquery()
is embedded in anotherselect()
construct.
-
method
sqlalchemy.orm.Query.
count()¶ Return a count of rows this the SQL formed by this
Query
would return.This generates the SQL for this Query as follows:
SELECT count(1) AS count_1 FROM ( SELECT <rest of query follows...> ) AS anon_1
The above SQL returns a single row, which is the aggregate value of the count function; the
Query.count()
method then returns that single integer value.Warning
It is important to note that the value returned by count() is not the same as the number of ORM objects that this Query would return from a method such as the .all() method. The
Query
object, when asked to return full entities, will deduplicate entries based on primary key, meaning if the same primary key value would appear in the results more than once, only one object of that primary key would be present. This does not apply to a query that is against individual columns.For fine grained control over specific columns to count, to skip the usage of a subquery or otherwise control of the FROM clause, or to use other aggregate functions, use
expression.func
expressions in conjunction withSession.query()
, i.e.:from sqlalchemy import func # count User records, without # using a subquery. session.query(func.count(User.id)) # return count of user "id" grouped # by "name" session.query(func.count(User.id)).\ group_by(User.name) from sqlalchemy import distinct # count distinct "name" values session.query(func.count(distinct(User.name)))
-
method
sqlalchemy.orm.Query.
cte(name=None, recursive=False, nesting=False)¶ Return the full SELECT statement represented by this
Query
represented as a common table expression (CTE).Parameters and usage are the same as those of the
SelectBase.cte()
method; see that method for further details.Here is the PostgreSQL WITH RECURSIVE example. Note that, in this example, the
included_parts
cte and theincl_alias
alias of it are Core selectables, which means the columns are accessed via the.c.
attribute. Theparts_alias
object is analiased()
instance of thePart
entity, so column-mapped attributes are available directly:from sqlalchemy.orm import aliased class Part(Base): __tablename__ = 'part' part = Column(String, primary_key=True) sub_part = Column(String, primary_key=True) quantity = Column(Integer) included_parts = session.query( Part.sub_part, Part.part, Part.quantity).\ filter(Part.part=="our part").\ cte(name="included_parts", recursive=True) incl_alias = aliased(included_parts, name="pr") parts_alias = aliased(Part, name="p") included_parts = included_parts.union_all( session.query( parts_alias.sub_part, parts_alias.part, parts_alias.quantity).\ filter(parts_alias.part==incl_alias.c.sub_part) ) q = session.query( included_parts.c.sub_part, func.sum(included_parts.c.quantity). label('total_quantity') ).\ group_by(included_parts.c.sub_part)
See also
-
method
sqlalchemy.orm.Query.
delete(synchronize_session='evaluate')¶ Perform a DELETE with an arbitrary WHERE clause.
Deletes rows matched by this query from the database.
E.g.:
sess.query(User).filter(User.age == 25).\ delete(synchronize_session=False) sess.query(User).filter(User.age == 25).\ delete(synchronize_session='evaluate')
Warning
See the section UPDATE and DELETE with arbitrary WHERE clause for important caveats and warnings, including limitations when using bulk UPDATE and DELETE with mapper inheritance configurations.
- Parameters:
synchronize_session¶ – chooses the strategy to update the attributes on objects in the session. See the section UPDATE and DELETE with arbitrary WHERE clause for a discussion of these strategies.
- Returns:
the count of rows matched as returned by the database’s “row count” feature.
-
method
sqlalchemy.orm.Query.
distinct(*expr)¶ Apply a
DISTINCT
to the query and return the newly resultingQuery
.Note
The ORM-level
distinct()
call includes logic that will automatically add columns from the ORDER BY of the query to the columns clause of the SELECT statement, to satisfy the common need of the database backend that ORDER BY columns be part of the SELECT list when DISTINCT is used. These columns are not added to the list of columns actually fetched by theQuery
, however, so would not affect results. The columns are passed through when using theQuery.statement
accessor, however.Deprecated since version 2.0: This logic is deprecated and will be removed in SQLAlchemy 2.0. See Using DISTINCT with additional columns, but only select the entity for a description of this use case in 2.0.
- Parameters:
*expr¶ –
optional column expressions. When present, the PostgreSQL dialect will render a
DISTINCT ON (<expressions>)
construct.Deprecated since version 1.4: Using *expr in other dialects is deprecated and will raise
CompileError
in a future version.
-
method
sqlalchemy.orm.Query.
enable_assertions(value)¶ Control whether assertions are generated.
When set to False, the returned Query will not assert its state before certain operations, including that LIMIT/OFFSET has not been applied when filter() is called, no criterion exists when get() is called, and no “from_statement()” exists when filter()/order_by()/group_by() etc. is called. This more permissive mode is used by custom Query subclasses to specify criterion or other modifiers outside of the usual usage patterns.
Care should be taken to ensure that the usage pattern is even possible. A statement applied by from_statement() will override any criterion set by filter() or order_by(), for example.
-
method
sqlalchemy.orm.Query.
enable_eagerloads(value)¶ Control whether or not eager joins and subqueries are rendered.
When set to False, the returned Query will not render eager joins regardless of
joinedload()
,subqueryload()
options or mapper-levellazy='joined'
/lazy='subquery'
configurations.This is used primarily when nesting the Query’s statement into a subquery or other selectable, or when using
Query.yield_per()
.
-
method
sqlalchemy.orm.Query.
except_(*q)¶ Produce an EXCEPT of this Query against one or more queries.
Works the same way as
Query.union()
. See that method for usage examples.
-
method
sqlalchemy.orm.Query.
except_all(*q)¶ Produce an EXCEPT ALL of this Query against one or more queries.
Works the same way as
Query.union()
. See that method for usage examples.
-
method
sqlalchemy.orm.Query.
execute(*multiparams, **params)¶ inherited from the
Executable.execute()
method ofExecutable
Compile and execute this
Executable
.Deprecated since version 1.4: The
Executable.execute()
method is considered legacy as of the 1.x series of SQLAlchemy and will be removed in 2.0. All statement execution in SQLAlchemy 2.0 is performed by theConnection.execute()
method ofConnection
, or in the ORM by theSession.execute()
method ofSession
. (Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)
-
method
sqlalchemy.orm.Query.
execution_options(**kwargs)¶ Set non-SQL options which take effect during execution.
Options allowed here include all of those accepted by
Connection.execution_options()
, as well as a series of ORM specific options:populate_existing=True
- equivalent to usingQuery.populate_existing()
autoflush=True|False
- equivalent to usingQuery.autoflush()
yield_per=<value>
- equivalent to usingQuery.yield_per()
Note that the
stream_results
execution option is enabled automatically if theQuery.yield_per()
method or execution option is used.New in version 1.4: - added ORM options to
Query.execution_options()
The execution options may also be specified on a per execution basis when using 2.0 style queries via the
Session.execution_options
parameter.Warning
The
Connection.execution_options.stream_results
parameter should not be used at the level of individual ORM statement executions, as theSession
will not track objects from different schema translate maps within a single session. For multiple schema translate maps within the scope of a singleSession
, see Horizontal Sharding.
-
method
sqlalchemy.orm.Query.
exists()¶ A convenience method that turns a query into an EXISTS subquery of the form EXISTS (SELECT 1 FROM … WHERE …).
e.g.:
q = session.query(User).filter(User.name == 'fred') session.query(q.exists())
Producing SQL similar to:
SELECT EXISTS ( SELECT 1 FROM users WHERE users.name = :name_1 ) AS anon_1
The EXISTS construct is usually used in the WHERE clause:
session.query(User.id).filter(q.exists()).scalar()
Note that some databases such as SQL Server don’t allow an EXISTS expression to be present in the columns clause of a SELECT. To select a simple boolean value based on the exists as a WHERE, use
literal()
:from sqlalchemy import literal session.query(literal(True)).filter(q.exists()).scalar()
-
method
sqlalchemy.orm.Query.
filter(*criterion)¶ Apply the given filtering criterion to a copy of this
Query
, using SQL expressions.e.g.:
session.query(MyClass).filter(MyClass.name == 'some name')
Multiple criteria may be specified as comma separated; the effect is that they will be joined together using the
and_()
function:session.query(MyClass).\ filter(MyClass.name == 'some name', MyClass.id > 5)
The criterion is any SQL expression object applicable to the WHERE clause of a select. String expressions are coerced into SQL expression constructs via the
text()
construct.See also
Query.filter_by()
- filter on keyword expressions.
-
method
sqlalchemy.orm.Query.
filter_by(**kwargs)¶ Apply the given filtering criterion to a copy of this
Query
, using keyword expressions.e.g.:
session.query(MyClass).filter_by(name = 'some name')
Multiple criteria may be specified as comma separated; the effect is that they will be joined together using the
and_()
function:session.query(MyClass).\ filter_by(name = 'some name', id = 5)
The keyword expressions are extracted from the primary entity of the query, or the last entity that was the target of a call to
Query.join()
.See also
Query.filter()
- filter on SQL expressions.
-
method
sqlalchemy.orm.Query.
first()¶ Return the first result of this
Query
or None if the result doesn’t contain any row.first() applies a limit of one within the generated SQL, so that only one primary entity row is generated on the server side (note this may consist of multiple result rows if join-loaded collections are present).
Calling
Query.first()
results in an execution of the underlying query.
-
method
sqlalchemy.orm.Query.
from_self(*entities)¶ return a Query that selects from this Query’s SELECT statement.
Deprecated since version 1.4: The
Query.from_self()
method is considered legacy as of the 1.x series of SQLAlchemy and will be removed in 2.0. The new approach is to use thealiased()
construct in conjunction with a subquery. See the section Selecting from the query itself as a subquery in the 2.0 migration notes for an example. (Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)Query.from_self()
essentially turns the SELECT statement into a SELECT of itself. Given a query such as:q = session.query(User).filter(User.name.like('e%'))
Given the
Query.from_self()
version:q = session.query(User).filter(User.name.like('e%')).from_self()
This query renders as:
SELECT anon_1.user_id AS anon_1_user_id, anon_1.user_name AS anon_1_user_name FROM (SELECT "user".id AS user_id, "user".name AS user_name FROM "user" WHERE "user".name LIKE :name_1) AS anon_1
There are lots of cases where
Query.from_self()
may be useful. A simple one is where above, we may want to apply a row LIMIT to the set of user objects we query against, and then apply additional joins against that row-limited set:q = session.query(User).filter(User.name.like('e%')).\ limit(5).from_self().\ join(User.addresses).filter(Address.email.like('q%'))
The above query joins to the
Address
entity but only against the first five results of theUser
query:SELECT anon_1.user_id AS anon_1_user_id, anon_1.user_name AS anon_1_user_name FROM (SELECT "user".id AS user_id, "user".name AS user_name FROM "user" WHERE "user".name LIKE :name_1 LIMIT :param_1) AS anon_1 JOIN address ON anon_1.user_id = address.user_id WHERE address.email LIKE :email_1
Automatic Aliasing
Another key behavior of
Query.from_self()
is that it applies automatic aliasing to the entities inside the subquery, when they are referenced on the outside. Above, if we continue to refer to theUser
entity without any additional aliasing applied to it, those references will be in terms of the subquery:q = session.query(User).filter(User.name.like('e%')).\ limit(5).from_self().\ join(User.addresses).filter(Address.email.like('q%')).\ order_by(User.name)
The ORDER BY against
User.name
is aliased to be in terms of the inner subquery:SELECT anon_1.user_id AS anon_1_user_id, anon_1.user_name AS anon_1_user_name FROM (SELECT "user".id AS user_id, "user".name AS user_name FROM "user" WHERE "user".name LIKE :name_1 LIMIT :param_1) AS anon_1 JOIN address ON anon_1.user_id = address.user_id WHERE address.email LIKE :email_1 ORDER BY anon_1.user_name
The automatic aliasing feature only works in a limited way, for simple filters and orderings. More ambitious constructions such as referring to the entity in joins should prefer to use explicit subquery objects, typically making use of the
Query.subquery()
method to produce an explicit subquery object. Always test the structure of queries by viewing the SQL to ensure a particular structure does what’s expected!Changing the Entities
Query.from_self()
also includes the ability to modify what columns are being queried. In our example, we wantUser.id
to be queried by the inner query, so that we can join to theAddress
entity on the outside, but we only wanted the outer query to return theAddress.email
column:q = session.query(User).filter(User.name.like('e%')).\ limit(5).from_self(Address.email).\ join(User.addresses).filter(Address.email.like('q%'))
yielding:
SELECT address.email AS address_email FROM (SELECT "user".id AS user_id, "user".name AS user_name FROM "user" WHERE "user".name LIKE :name_1 LIMIT :param_1) AS anon_1 JOIN address ON anon_1.user_id = address.user_id WHERE address.email LIKE :email_1
Looking out for Inner / Outer Columns
Keep in mind that when referring to columns that originate from inside the subquery, we need to ensure they are present in the columns clause of the subquery itself; this is an ordinary aspect of SQL. For example, if we wanted to load from a joined entity inside the subquery using
contains_eager()
, we need to add those columns. Below illustrates a join ofAddress
toUser
, then a subquery, and then we’d likecontains_eager()
to access theUser
columns:q = session.query(Address).join(Address.user).\ filter(User.name.like('e%')) q = q.add_entity(User).from_self().\ options(contains_eager(Address.user))
We use
Query.add_entity()
above before we callQuery.from_self()
so that theUser
columns are present in the inner subquery, so that they are available to thecontains_eager()
modifier we are using on the outside, producing:SELECT anon_1.address_id AS anon_1_address_id, anon_1.address_email AS anon_1_address_email, anon_1.address_user_id AS anon_1_address_user_id, anon_1.user_id AS anon_1_user_id, anon_1.user_name AS anon_1_user_name FROM ( SELECT address.id AS address_id, address.email AS address_email, address.user_id AS address_user_id, "user".id AS user_id, "user".name AS user_name FROM address JOIN "user" ON "user".id = address.user_id WHERE "user".name LIKE :name_1) AS anon_1
If we didn’t call
add_entity(User)
, but still askedcontains_eager()
to load theUser
entity, it would be forced to add the table on the outside without the correct join criteria - note theanon1, "user"
phrase at the end:-- incorrect query SELECT anon_1.address_id AS anon_1_address_id, anon_1.address_email AS anon_1_address_email, anon_1.address_user_id AS anon_1_address_user_id, "user".id AS user_id, "user".name AS user_name FROM ( SELECT address.id AS address_id, address.email AS address_email, address.user_id AS address_user_id FROM address JOIN "user" ON "user".id = address.user_id WHERE "user".name LIKE :name_1) AS anon_1, "user"
- Parameters:
*entities¶ – optional list of entities which will replace those being selected.
-
method
sqlalchemy.orm.Query.
from_statement(statement)¶ Execute the given SELECT statement and return results.
This method bypasses all internal statement compilation, and the statement is executed without modification.
The statement is typically either a
text()
orselect()
construct, and should return the set of columns appropriate to the entity class represented by thisQuery
.See also
Using Textual SQL - usage examples in the ORM tutorial
-
method
sqlalchemy.orm.Query.
get(ident)¶ Return an instance based on the given primary key identifier, or
None
if not found.Deprecated since version 1.4: The
Query.get()
method is considered legacy as of the 1.x series of SQLAlchemy and becomes a legacy construct in 2.0. The method is now available asSession.get()
(Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)E.g.:
my_user = session.query(User).get(5) some_object = session.query(VersionedFoo).get((5, 10)) some_object = session.query(VersionedFoo).get( {"id": 5, "version_id": 10})
Query.get()
is special in that it provides direct access to the identity map of the owningSession
. If the given primary key identifier is present in the local identity map, the object is returned directly from this collection and no SQL is emitted, unless the object has been marked fully expired. If not present, a SELECT is performed in order to locate the object.Query.get()
also will perform a check if the object is present in the identity map and marked as expired - a SELECT is emitted to refresh the object as well as to ensure that the row is still present. If not,ObjectDeletedError
is raised.Query.get()
is only used to return a single mapped instance, not multiple instances or individual column constructs, and strictly on a single primary key value. The originatingQuery
must be constructed in this way, i.e. against a single mapped entity, with no additional filtering criterion. Loading options viaQuery.options()
may be applied however, and will be used if the object is not yet locally present.- Parameters:
ident¶ –
A scalar, tuple, or dictionary representing the primary key. For a composite (e.g. multiple column) primary key, a tuple or dictionary should be passed.
For a single-column primary key, the scalar calling form is typically the most expedient. If the primary key of a row is the value “5”, the call looks like:
my_object = query.get(5)
The tuple form contains primary key values typically in the order in which they correspond to the mapped
Table
object’s primary key columns, or if theMapper.primary_key
configuration parameter were used, in the order used for that parameter. For example, if the primary key of a row is represented by the integer digits “5, 10” the call would look like:my_object = query.get((5, 10))
The dictionary form should include as keys the mapped attribute names corresponding to each element of the primary key. If the mapped class has the attributes
id
,version_id
as the attributes which store the object’s primary key value, the call would look like:my_object = query.get({"id": 5, "version_id": 10})
New in version 1.3: the
Query.get()
method now optionally accepts a dictionary of attribute names to values in order to indicate a primary key identifier.- Returns:
The object instance, or
None
.
-
method
sqlalchemy.orm.Query.
get_execution_options()¶ Get the non-SQL options which will take effect during execution.
New in version 1.3.
See also
-
attribute
sqlalchemy.orm.Query.
get_label_style¶ Retrieve the current label style.
New in version 1.4.
-
method
sqlalchemy.orm.Query.
group_by(*clauses)¶ Apply one or more GROUP BY criterion to the query and return the newly resulting
Query
.All existing GROUP BY settings can be suppressed by passing
None
- this will suppress any GROUP BY configured on mappers as well.See also
These sections describe GROUP BY in terms of 2.0 style invocation but apply to
Query
as well:Aggregate functions with GROUP BY / HAVING - in the SQLAlchemy 1.4 / 2.0 Tutorial
Ordering or Grouping by a Label - in the SQLAlchemy 1.4 / 2.0 Tutorial
-
method
sqlalchemy.orm.Query.
having(criterion)¶ Apply a HAVING criterion to the query and return the newly resulting
Query
.Query.having()
is used in conjunction withQuery.group_by()
.HAVING criterion makes it possible to use filters on aggregate functions like COUNT, SUM, AVG, MAX, and MIN, eg.:
q = session.query(User.id).\ join(User.addresses).\ group_by(User.id).\ having(func.count(Address.id) > 2)
-
method
sqlalchemy.orm.Query.
instances(result_proxy, context=None)¶ Return an ORM result given a
CursorResult
andQueryContext
.
-
method
sqlalchemy.orm.Query.
intersect(*q)¶ Produce an INTERSECT of this Query against one or more queries.
Works the same way as
Query.union()
. See that method for usage examples.
-
method
sqlalchemy.orm.Query.
intersect_all(*q)¶ Produce an INTERSECT ALL of this Query against one or more queries.
Works the same way as
Query.union()
. See that method for usage examples.
-
attribute
sqlalchemy.orm.Query.
is_single_entity¶ Indicates if this
Query
returns tuples or single entities.Returns True if this query returns a single entity for each instance in its result list, and False if this query returns a tuple of entities for each result.
New in version 1.3.11.
See also
-
method
sqlalchemy.orm.Query.
join(target, *props, **kwargs)¶ Create a SQL JOIN against this
Query
object’s criterion and apply generatively, returning the newly resultingQuery
.Simple Relationship Joins
Consider a mapping between two classes
User
andAddress
, with a relationshipUser.addresses
representing a collection ofAddress
objects associated with eachUser
. The most common usage ofQuery.join()
is to create a JOIN along this relationship, using theUser.addresses
attribute as an indicator for how this should occur:q = session.query(User).join(User.addresses)
Where above, the call to
Query.join()
alongUser.addresses
will result in SQL approximately equivalent to:SELECT user.id, user.name FROM user JOIN address ON user.id = address.user_id
In the above example we refer to
User.addresses
as passed toQuery.join()
as the “on clause”, that is, it indicates how the “ON” portion of the JOIN should be constructed.To construct a chain of joins, multiple
Query.join()
calls may be used. The relationship-bound attribute implies both the left and right side of the join at once:q = session.query(User).\ join(User.orders).\ join(Order.items).\ join(Item.keywords)
Note
as seen in the above example, the order in which each call to the join() method occurs is important. Query would not, for example, know how to join correctly if we were to specify
User
, thenItem
, thenOrder
, in our chain of joins; in such a case, depending on the arguments passed, it may raise an error that it doesn’t know how to join, or it may produce invalid SQL in which case the database will raise an error. In correct practice, theQuery.join()
method is invoked in such a way that lines up with how we would want the JOIN clauses in SQL to be rendered, and each call should represent a clear link from what precedes it.Joins to a Target Entity or Selectable
A second form of
Query.join()
allows any mapped entity or core selectable construct as a target. In this usage,Query.join()
will attempt to create a JOIN along the natural foreign key relationship between two entities:q = session.query(User).join(Address)
In the above calling form,
Query.join()
is called upon to create the “on clause” automatically for us. This calling form will ultimately raise an error if either there are no foreign keys between the two entities, or if there are multiple foreign key linkages between the target entity and the entity or entities already present on the left side such that creating a join requires more information. Note that when indicating a join to a target without any ON clause, ORM configured relationships are not taken into account.Joins to a Target with an ON Clause
The third calling form allows both the target entity as well as the ON clause to be passed explicitly. A example that includes a SQL expression as the ON clause is as follows:
q = session.query(User).join(Address, User.id==Address.user_id)
The above form may also use a relationship-bound attribute as the ON clause as well:
q = session.query(User).join(Address, User.addresses)
The above syntax can be useful for the case where we wish to join to an alias of a particular target entity. If we wanted to join to
Address
twice, it could be achieved using two aliases set up using thealiased()
function:a1 = aliased(Address) a2 = aliased(Address) q = session.query(User).\ join(a1, User.addresses).\ join(a2, User.addresses).\ filter(a1.email_address=='ed@foo.com').\ filter(a2.email_address=='ed@bar.com')
The relationship-bound calling form can also specify a target entity using the
PropComparator.of_type()
method; a query equivalent to the one above would be:a1 = aliased(Address) a2 = aliased(Address) q = session.query(User).\ join(User.addresses.of_type(a1)).\ join(User.addresses.of_type(a2)).\ filter(a1.email_address == 'ed@foo.com').\ filter(a2.email_address == 'ed@bar.com')
Augmenting Built-in ON Clauses
As a substitute for providing a full custom ON condition for an existing relationship, the
PropComparator.and_()
function may be applied to a relationship attribute to augment additional criteria into the ON clause; the additional criteria will be combined with the default criteria using AND:q = session.query(User).join( User.addresses.and_(Address.email_address != 'foo@bar.com') )
New in version 1.4.
Joining to Tables and Subqueries
The target of a join may also be any table or SELECT statement, which may be related to a target entity or not. Use the appropriate
.subquery()
method in order to make a subquery out of a query:subq = session.query(Address).\ filter(Address.email_address == 'ed@foo.com').\ subquery() q = session.query(User).join( subq, User.id == subq.c.user_id )
Joining to a subquery in terms of a specific relationship and/or target entity may be achieved by linking the subquery to the entity using
aliased()
:subq = session.query(Address).\ filter(Address.email_address == 'ed@foo.com').\ subquery() address_subq = aliased(Address, subq) q = session.query(User).join( User.addresses.of_type(address_subq) )
Controlling what to Join From
In cases where the left side of the current state of
Query
is not in line with what we want to join from, theQuery.select_from()
method may be used:q = session.query(Address).select_from(User).\ join(User.addresses).\ filter(User.name == 'ed')
Which will produce SQL similar to:
SELECT address.* FROM user JOIN address ON user.id=address.user_id WHERE user.name = :name_1
Legacy Features of Query.join()
Deprecated since version 1.4: The following features are deprecated and will be removed in SQLAlchemy 2.0.
The
Query.join()
method currently supports several usage patterns and arguments that are considered to be legacy as of SQLAlchemy 1.3. A deprecation path will follow in the 1.4 series for the following features:Joining on relationship names rather than attributes:
session.query(User).join("addresses")
Why it’s legacy: the string name does not provide enough context for
Query.join()
to always know what is desired, notably in that there is no indication of what the left side of the join should be. This gives rise to flags likefrom_joinpoint
as well as the ability to place several join clauses in a singleQuery.join()
call which don’t solve the problem fully while also adding new calling styles that are unnecessary and expensive to accommodate internally.Modern calling pattern: Use the actual relationship, e.g.
User.addresses
in the above case:session.query(User).join(User.addresses)
Automatic aliasing with the
aliased=True
flag:session.query(Node).join(Node.children, aliased=True).\ filter(Node.name == 'some name')
Why it’s legacy: the automatic aliasing feature of
Query
is intensely complicated, both in its internal implementation as well as in its observed behavior, and is almost never used. It is difficult to know upon inspection where and when its aliasing of a target entity,Node
in the above case, will be applied and when it won’t, and additionally the feature has to use very elaborate heuristics to achieve this implicit behavior.Modern calling pattern: Use the
aliased()
construct explicitly:from sqlalchemy.orm import aliased n1 = aliased(Node) session.query(Node).join(Node.children.of_type(n1)).\ filter(n1.name == 'some name')
Multiple joins in one call:
session.query(User).join("orders", "items") session.query(User).join(User.orders, Order.items) session.query(User).join( (Order, User.orders), (Item, Item.order_id == Order.id) ) session.query(User).join(Order, Item) # ... and several more forms actually
Why it’s legacy: being able to chain multiple ON clauses in one call to
Query.join()
is yet another attempt to solve the problem of being able to specify what entity to join from, and is the source of a large variety of potential calling patterns that are internally expensive and complicated to parse and accommodate.Modern calling pattern: Use relationship-bound attributes or SQL-oriented ON clauses within separate calls, so that each call to
Query.join()
knows what the left side should be:session.query(User).join(User.orders).join( Item, Item.order_id == Order.id)
- Parameters:
*props¶ – Incoming arguments for
Query.join()
, the props collection in modern use should be considered to be a one or two argument form, either as a single “target” entity or ORM attribute-bound relationship, or as a target entity plus an “on clause” which may be a SQL expression or ORM attribute-bound relationship.isouter=False¶ – If True, the join used will be a left outer join, just as if the
Query.outerjoin()
method were called.full=False¶ –
render FULL OUTER JOIN; implies
isouter
.New in version 1.1.
from_joinpoint=False¶ –
When using
aliased=True
, a setting of True here will cause the join to be from the most recent joined target, rather than starting back from the original FROM clauses of the query.Note
This flag is considered legacy.
aliased=False¶ –
If True, indicate that the JOIN target should be anonymously aliased. Subsequent calls to
Query.filter()
and similar will adapt the incoming criterion to the target alias, untilQuery.reset_joinpoint()
is called.Note
This flag is considered legacy.
See also
Querying with Joins in the ORM tutorial.
Mapping Class Inheritance Hierarchies for details on how
Query.join()
is used for inheritance relationships.join()
- a standalone ORM-level join function, used internally byQuery.join()
, which in previous SQLAlchemy versions was the primary ORM-level joining interface.
-
method
sqlalchemy.orm.Query.
label(name)¶ Return the full SELECT statement represented by this
Query
, converted to a scalar subquery with a label of the given name.Analogous to
SelectBase.label()
.
-
attribute
sqlalchemy.orm.Query.
lazy_loaded_from¶ An
InstanceState
that is using thisQuery
for a lazy load operation.Deprecated since version 1.4: This attribute should be viewed via the
ORMExecuteState.lazy_loaded_from
attribute, within the context of theSessionEvents.do_orm_execute()
event.See also
-
method
sqlalchemy.orm.Query.
limit(limit)¶ Apply a
LIMIT
to the query and return the newly resultingQuery
.
-
classmethod
sqlalchemy.orm.Query.
memoized_instancemethod(fn)¶ inherited from the
HasMemoized.memoized_instancemethod()
method ofHasMemoized
Decorate a method memoize its return value.
-
method
sqlalchemy.orm.Query.
merge_result(iterator, load=True)¶ Merge a result into this
Query
object’s Session.Deprecated since version 1.4: The
Query.merge_result()
method is considered legacy as of the 1.x series of SQLAlchemy and becomes a legacy construct in 2.0. The method is superseded by themerge_frozen_result()
function. (Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)Given an iterator returned by a
Query
of the same structure as this one, return an identical iterator of results, with all mapped instances merged into the session usingSession.merge()
. This is an optimized method which will merge all mapped instances, preserving the structure of the result rows and unmapped columns with less method overhead than that of callingSession.merge()
explicitly for each value.The structure of the results is determined based on the column list of this
Query
- if these do not correspond, unchecked errors will occur.The ‘load’ argument is the same as that of
Session.merge()
.For an example of how
Query.merge_result()
is used, see the source code for the example Dogpile Caching, whereQuery.merge_result()
is used to efficiently restore state from a cache back into a targetSession
.
-
method
sqlalchemy.orm.Query.
offset(offset)¶ Apply an
OFFSET
to the query and return the newly resultingQuery
.
-
method
sqlalchemy.orm.Query.
one()¶ Return exactly one result or raise an exception.
Raises
sqlalchemy.orm.exc.NoResultFound
if the query selects no rows. Raisessqlalchemy.orm.exc.MultipleResultsFound
if multiple object identities are returned, or if multiple rows are returned for a query that returns only scalar values as opposed to full identity-mapped entities.Calling
one()
results in an execution of the underlying query.
-
method
sqlalchemy.orm.Query.
one_or_none()¶ Return at most one result or raise an exception.
Returns
None
if the query selects no rows. Raisessqlalchemy.orm.exc.MultipleResultsFound
if multiple object identities are returned, or if multiple rows are returned for a query that returns only scalar values as opposed to full identity-mapped entities.Calling
Query.one_or_none()
results in an execution of the underlying query.New in version 1.0.9: Added
Query.one_or_none()
-
method
sqlalchemy.orm.Query.
only_return_tuples(value)¶ When set to True, the query results will always be a tuple.
This is specifically for single element queries. The default is False.
New in version 1.2.5.
See also
-
method
sqlalchemy.orm.Query.
options(*args)¶ Return a new
Query
object, applying the given list of mapper options.Most supplied options regard changing how column- and relationship-mapped attributes are loaded.
-
method
sqlalchemy.orm.Query.
order_by(*clauses)¶ Apply one or more ORDER BY criteria to the query and return the newly resulting
Query
.e.g.:
q = session.query(Entity).order_by(Entity.id, Entity.name)
Calling this method multiple times is equivalent to calling it once with all the clauses concatenated. All existing ORDER BY criteria may be cancelled by passing
None
by itself. New ORDER BY criteria may then be added by invokingQuery.order_by()
again, e.g.:# will erase all ORDER BY and ORDER BY new_col alone q = q.order_by(None).order_by(new_col)
See also
These sections describe ORDER BY in terms of 2.0 style invocation but apply to
Query
as well:ORDER BY - in the SQLAlchemy 1.4 / 2.0 Tutorial
Ordering or Grouping by a Label - in the SQLAlchemy 1.4 / 2.0 Tutorial
-
method
sqlalchemy.orm.Query.
outerjoin(target, *props, **kwargs)¶ Create a left outer join against this
Query
object’s criterion and apply generatively, returning the newly resultingQuery
.Usage is the same as the
join()
method.
-
method
sqlalchemy.orm.Query.
params(*args, **kwargs)¶ Add values for bind parameters which may have been specified in filter().
Parameters may be specified using **kwargs, or optionally a single dictionary as the first positional argument. The reason for both is that **kwargs is convenient, however some parameter dictionaries contain unicode keys in which case **kwargs cannot be used.
-
method
sqlalchemy.orm.Query.
populate_existing()¶ Return a
Query
that will expire and refresh all instances as they are loaded, or reused from the currentSession
.As of SQLAlchemy 1.4, the
Query.populate_existing()
method is equivalent to using thepopulate_existing
execution option at the ORM level. See the section Populate Existing for further background on this option.
-
method
sqlalchemy.orm.Query.
prefix_with(*expr, **kw)¶ inherited from the
HasPrefixes.prefix_with()
method ofHasPrefixes
Add one or more expressions following the statement keyword, i.e. SELECT, INSERT, UPDATE, or DELETE. Generative.
This is used to support backend-specific prefix keywords such as those provided by MySQL.
E.g.:
stmt = table.insert().prefix_with("LOW_PRIORITY", dialect="mysql") # MySQL 5.7 optimizer hints stmt = select(table).prefix_with( "/*+ BKA(t1) */", dialect="mysql")
Multiple prefixes can be specified by multiple calls to
HasPrefixes.prefix_with()
.- Parameters:
*expr¶ – textual or
ClauseElement
construct which will be rendered following the INSERT, UPDATE, or DELETE keyword.**kw¶ – A single keyword ‘dialect’ is accepted. This is an optional string dialect name which will limit rendering of this prefix to only that dialect.
-
method
sqlalchemy.orm.Query.
reset_joinpoint()¶ Return a new
Query
, where the “join point” has been reset back to the base FROM entities of the query.This method is usually used in conjunction with the
aliased=True
feature of theQuery.join()
method. See the example inQuery.join()
for how this is used.
-
method
sqlalchemy.orm.Query.
scalar()¶ Return the first element of the first result or None if no rows present. If multiple rows are returned, raises MultipleResultsFound.
>>> session.query(Item).scalar() <Item> >>> session.query(Item.id).scalar() 1 >>> session.query(Item.id).filter(Item.id < 0).scalar() None >>> session.query(Item.id, Item.name).scalar() 1 >>> session.query(func.count(Parent.id)).scalar() 20
This results in an execution of the underlying query.
-
method
sqlalchemy.orm.Query.
scalar_subquery()¶ Return the full SELECT statement represented by this
Query
, converted to a scalar subquery.Analogous to
SelectBase.scalar_subquery()
.Changed in version 1.4: The
Query.scalar_subquery()
method replaces theQuery.as_scalar()
method.
-
method
sqlalchemy.orm.Query.
select_entity_from(from_obj)¶ Set the FROM clause of this
Query
to a core selectable, applying it as a replacement FROM clause for corresponding mapped entities.Deprecated since version 1.4: The
Query.select_entity_from()
method is considered legacy as of the 1.x series of SQLAlchemy and will be removed in 2.0. Use thealiased()
construct instead (Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)The
Query.select_entity_from()
method supplies an alternative approach to the use case of applying analiased()
construct explicitly throughout a query. Instead of referring to thealiased()
construct explicitly,Query.select_entity_from()
automatically adapts all occurrences of the entity to the target selectable.Given a case for
aliased()
such as selectingUser
objects from a SELECT statement:select_stmt = select(User).where(User.id == 7) user_alias = aliased(User, select_stmt) q = session.query(user_alias).\ filter(user_alias.name == 'ed')
Above, we apply the
user_alias
object explicitly throughout the query. When it’s not feasible foruser_alias
to be referenced explicitly in many places,Query.select_entity_from()
may be used at the start of the query to adapt the existingUser
entity:q = session.query(User).\ select_entity_from(select_stmt.subquery()).\ filter(User.name == 'ed')
Above, the generated SQL will show that the
User
entity is adapted to our statement, even in the case of the WHERE clause:SELECT anon_1.id AS anon_1_id, anon_1.name AS anon_1_name FROM (SELECT "user".id AS id, "user".name AS name FROM "user" WHERE "user".id = :id_1) AS anon_1 WHERE anon_1.name = :name_1
The
Query.select_entity_from()
method is similar to theQuery.select_from()
method, in that it sets the FROM clause of the query. The difference is that it additionally applies adaptation to the other parts of the query that refer to the primary entity. If above we had usedQuery.select_from()
instead, the SQL generated would have been:-- uses plain select_from(), not select_entity_from() SELECT "user".id AS user_id, "user".name AS user_name FROM "user", (SELECT "user".id AS id, "user".name AS name FROM "user" WHERE "user".id = :id_1) AS anon_1 WHERE "user".name = :name_1
To supply textual SQL to the
Query.select_entity_from()
method, we can make use of thetext()
construct. However, thetext()
construct needs to be aligned with the columns of our entity, which is achieved by making use of theTextClause.columns()
method:text_stmt = text("select id, name from user").columns( User.id, User.name).subquery() q = session.query(User).select_entity_from(text_stmt)
Query.select_entity_from()
itself accepts analiased()
object, so that the special options ofaliased()
such asaliased.adapt_on_names
may be used within the scope of theQuery.select_entity_from()
method’s adaptation services. Suppose a viewuser_view
also returns rows fromuser
. If we reflect this view into aTable
, this view has no relationship to theTable
to which we are mapped, however we can use name matching to select from it:user_view = Table('user_view', metadata, autoload_with=engine) user_view_alias = aliased( User, user_view, adapt_on_names=True) q = session.query(User).\ select_entity_from(user_view_alias).\ order_by(User.name)
Changed in version 1.1.7: The
Query.select_entity_from()
method now accepts analiased()
object as an alternative to aFromClause
object.- Parameters:
from_obj¶ – a
FromClause
object that will replace the FROM clause of thisQuery
. It also may be an instance ofaliased()
.
See also
-
method
sqlalchemy.orm.Query.
select_from(*from_obj)¶ Set the FROM clause of this
Query
explicitly.Query.select_from()
is often used in conjunction withQuery.join()
in order to control which entity is selected from on the “left” side of the join.The entity or selectable object here effectively replaces the “left edge” of any calls to
Query.join()
, when no joinpoint is otherwise established - usually, the default “join point” is the leftmost entity in theQuery
object’s list of entities to be selected.A typical example:
q = session.query(Address).select_from(User).\ join(User.addresses).\ filter(User.name == 'ed')
Which produces SQL equivalent to:
SELECT address.* FROM user JOIN address ON user.id=address.user_id WHERE user.name = :name_1
- Parameters:
*from_obj¶ – collection of one or more entities to apply to the FROM clause. Entities can be mapped classes,
AliasedClass
objects,Mapper
objects as well as coreFromClause
elements like subqueries.
Changed in version 0.9: This method no longer applies the given FROM object to be the selectable from which matching entities select from; the
select_entity_from()
method now accomplishes this. See that method for a description of this behavior.
-
attribute
sqlalchemy.orm.Query.
selectable¶ Return the
Select
object emitted by thisQuery
.Used for
inspect()
compatibility, this is equivalent to:query.enable_eagerloads(False).with_labels().statement
-
method
sqlalchemy.orm.Query.
set_label_style(style)¶ Apply column labels to the return value of Query.statement.
Indicates that this Query’s statement accessor should return a SELECT statement that applies labels to all columns in the form <tablename>_<columnname>; this is commonly used to disambiguate columns from multiple tables which have the same name.
When the Query actually issues SQL to load rows, it always uses column labeling.
Note
The
Query.set_label_style()
method only applies the output ofQuery.statement
, and not to any of the result-row invoking systems ofQuery
itself, e.g.Query.first()
,Query.all()
, etc. To execute a query usingQuery.set_label_style()
, invoke theQuery.statement
usingSession.execute()
:result = session.execute( query .set_label_style(LABEL_STYLE_TABLENAME_PLUS_COL) .statement )
New in version 1.4.
-
method
sqlalchemy.orm.Query.
slice(start, stop)¶ Computes the “slice” of the
Query
represented by the given indices and returns the resultingQuery
.The start and stop indices behave like the argument to Python’s built-in
range()
function. This method provides an alternative to usingLIMIT
/OFFSET
to get a slice of the query.For example,
session.query(User).order_by(User.id).slice(1, 3)
renders as
SELECT users.id AS users_id, users.name AS users_name FROM users ORDER BY users.id LIMIT ? OFFSET ? (2, 1)
-
attribute
sqlalchemy.orm.Query.
statement¶ The full SELECT statement represented by this Query.
The statement by default will not have disambiguating labels applied to the construct unless with_labels(True) is called first.
-
method
sqlalchemy.orm.Query.
subquery(name=None, with_labels=False, reduce_columns=False)¶ Return the full SELECT statement represented by this
Query
, embedded within anAlias
.Eager JOIN generation within the query is disabled.
- Parameters:
name¶ – string name to be assigned as the alias; this is passed through to
FromClause.alias()
. IfNone
, a name will be deterministically generated at compile time.with_labels¶ – if True,
with_labels()
will be called on theQuery
first to apply table-qualified labels to all columns.reduce_columns¶ – if True,
Select.reduce_columns()
will be called on the resultingselect()
construct, to remove same-named columns where one also refers to the other via foreign key or WHERE clause equivalence.
-
method
sqlalchemy.orm.Query.
suffix_with(*expr, **kw)¶ inherited from the
HasSuffixes.suffix_with()
method ofHasSuffixes
Add one or more expressions following the statement as a whole.
This is used to support backend-specific suffix keywords on certain constructs.
E.g.:
stmt = select(col1, col2).cte().suffix_with( "cycle empno set y_cycle to 1 default 0", dialect="oracle")
Multiple suffixes can be specified by multiple calls to
HasSuffixes.suffix_with()
.- Parameters:
*expr¶ – textual or
ClauseElement
construct which will be rendered following the target clause.**kw¶ – A single keyword ‘dialect’ is accepted. This is an optional string dialect name which will limit rendering of this suffix to only that dialect.
-
method
sqlalchemy.orm.Query.
union(*q)¶ Produce a UNION of this Query against one or more queries.
e.g.:
q1 = sess.query(SomeClass).filter(SomeClass.foo=='bar') q2 = sess.query(SomeClass).filter(SomeClass.bar=='foo') q3 = q1.union(q2)
The method accepts multiple Query objects so as to control the level of nesting. A series of
union()
calls such as:x.union(y).union(z).all()
will nest on each
union()
, and produces:SELECT * FROM (SELECT * FROM (SELECT * FROM X UNION SELECT * FROM y) UNION SELECT * FROM Z)
Whereas:
x.union(y, z).all()
produces:
SELECT * FROM (SELECT * FROM X UNION SELECT * FROM y UNION SELECT * FROM Z)
Note that many database backends do not allow ORDER BY to be rendered on a query called within UNION, EXCEPT, etc. To disable all ORDER BY clauses including those configured on mappers, issue
query.order_by(None)
- the resultingQuery
object will not render ORDER BY within its SELECT statement.
-
method
sqlalchemy.orm.Query.
union_all(*q)¶ Produce a UNION ALL of this Query against one or more queries.
Works the same way as
Query.union()
. See that method for usage examples.
-
method
sqlalchemy.orm.Query.
update(values, synchronize_session='evaluate', update_args=None)¶ Perform an UPDATE with an arbitrary WHERE clause.
Updates rows matched by this query in the database.
E.g.:
sess.query(User).filter(User.age == 25).\ update({User.age: User.age - 10}, synchronize_session=False) sess.query(User).filter(User.age == 25).\ update({"age": User.age - 10}, synchronize_session='evaluate')
Warning
See the section UPDATE and DELETE with arbitrary WHERE clause for important caveats and warnings, including limitations when using arbitrary UPDATE and DELETE with mapper inheritance configurations.
- Parameters:
values¶ – a dictionary with attributes names, or alternatively mapped attributes or SQL expressions, as keys, and literal values or sql expressions as values. If parameter-ordered mode is desired, the values can be passed as a list of 2-tuples; this requires that the
update.preserve_parameter_order
flag is passed to theQuery.update.update_args
dictionary as well.synchronize_session¶ – chooses the strategy to update the attributes on objects in the session. See the section UPDATE and DELETE with arbitrary WHERE clause for a discussion of these strategies.
update_args¶ – Optional dictionary, if present will be passed to the underlying
update()
construct as the**kw
for the object. May be used to pass dialect-specific arguments such asmysql_limit
, as well as other special arguments such asupdate.preserve_parameter_order
.
- Returns:
the count of rows matched as returned by the database’s “row count” feature.
-
method
sqlalchemy.orm.Query.
value(column)¶ Return a scalar result corresponding to the given column expression.
Deprecated since version 1.4:
Query.value()
is deprecated and will be removed in a future release. Please useQuery.with_entities()
in combination withQuery.scalar()
-
method
sqlalchemy.orm.Query.
values(*columns)¶ Return an iterator yielding result tuples corresponding to the given list of columns
Deprecated since version 1.4:
Query.values()
is deprecated and will be removed in a future release. Please useQuery.with_entities()
-
method
sqlalchemy.orm.Query.
where(*criterion)¶ A synonym for
Query.filter()
.New in version 1.4.
-
attribute
sqlalchemy.orm.Query.
whereclause¶ A readonly attribute which returns the current WHERE criterion for this Query.
This returned value is a SQL expression construct, or
None
if no criterion has been established.
-
method
sqlalchemy.orm.Query.
with_entities(*entities)¶ Return a new
Query
replacing the SELECT list with the given entities.e.g.:
# Users, filtered on some arbitrary criterion # and then ordered by related email address q = session.query(User).\ join(User.address).\ filter(User.name.like('%ed%')).\ order_by(Address.email) # given *only* User.id==5, Address.email, and 'q', what # would the *next* User in the result be ? subq = q.with_entities(Address.email).\ order_by(None).\ filter(User.id==5).\ subquery() q = q.join((subq, subq.c.email < Address.email)).\ limit(1)
-
method
sqlalchemy.orm.Query.
with_for_update(read=False, nowait=False, of=None, skip_locked=False, key_share=False)¶ return a new
Query
with the specified options for theFOR UPDATE
clause.The behavior of this method is identical to that of
GenerativeSelect.with_for_update()
. When called with no arguments, the resultingSELECT
statement will have aFOR UPDATE
clause appended. When additional arguments are specified, backend-specific options such asFOR UPDATE NOWAIT
orLOCK IN SHARE MODE
can take effect.E.g.:
q = sess.query(User).populate_existing().with_for_update(nowait=True, of=User)
The above query on a PostgreSQL backend will render like:
SELECT users.id AS users_id FROM users FOR UPDATE OF users NOWAIT
Warning
Using
with_for_update
in the context of eager loading relationships is not officially supported or recommended by SQLAlchemy and may not work with certain queries on various database backends. Whenwith_for_update
is successfully used with a query that involvesjoinedload()
, SQLAlchemy will attempt to emit SQL that locks all involved tables.Note
It is generally a good idea to combine the use of the
Query.populate_existing()
method when using theQuery.with_for_update()
method. The purpose ofQuery.populate_existing()
is to force all the data read from the SELECT to be populated into the ORM objects returned, even if these objects are already in the identity map.See also
GenerativeSelect.with_for_update()
- Core level method with full argument and behavioral description.Query.populate_existing()
- overwrites attributes of objects already loaded in the identity map.
-
method
sqlalchemy.orm.Query.
with_hint(selectable, text, dialect_name='*')¶ inherited from the
HasHints.with_hint()
method ofHasHints
Add an indexing or other executional context hint for the given selectable to this
Select
or other selectable object.The text of the hint is rendered in the appropriate location for the database backend in use, relative to the given
Table
orAlias
passed as theselectable
argument. The dialect implementation typically uses Python string substitution syntax with the token%(name)s
to render the name of the table or alias. E.g. when using Oracle, the following:select(mytable).\ with_hint(mytable, "index(%(name)s ix_mytable)")
Would render SQL as:
select /*+ index(mytable ix_mytable) */ ... from mytable
The
dialect_name
option will limit the rendering of a particular hint to a particular backend. Such as, to add hints for both Oracle and Sybase simultaneously:select(mytable).\ with_hint(mytable, "index(%(name)s ix_mytable)", 'oracle').\ with_hint(mytable, "WITH INDEX ix_mytable", 'sybase')
See also
-
method
sqlalchemy.orm.Query.
with_labels()¶ Deprecated since version 1.4: The
Query.with_labels()
andQuery.apply_labels()
method is considered legacy as of the 1.x series of SQLAlchemy and will be removed in 2.0. Use set_label_style(LABEL_STYLE_TABLENAME_PLUS_COL) instead. (Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)
-
method
sqlalchemy.orm.Query.
with_parent(instance, property=None, from_entity=None)¶ Add filtering criterion that relates the given instance to a child object or collection, using its attribute state as well as an established
relationship()
configuration.Deprecated since version 1.4: The
Query.with_parent()
method is considered legacy as of the 1.x series of SQLAlchemy and becomes a legacy construct in 2.0. Use thewith_parent()
standalone construct. (Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)The method uses the
with_parent()
function to generate the clause, the result of which is passed toQuery.filter()
.Parameters are the same as
with_parent()
, with the exception that the given property can be None, in which case a search is performed against thisQuery
object’s target mapper.- Parameters:
instance¶ – An instance which has some
relationship()
.property¶ – String property name, or class-bound attribute, which indicates what relationship from the instance should be used to reconcile the parent/child relationship.
from_entity¶ – Entity in which to consider as the left side. This defaults to the “zero” entity of the
Query
itself.
-
method
sqlalchemy.orm.Query.
with_polymorphic(cls_or_mappers, selectable=None, polymorphic_on=None)¶ Load columns for inheriting classes.
Deprecated since version 1.4: The
Query.with_polymorphic()
method is considered legacy as of the 1.x series of SQLAlchemy and will be removed in 2.0. Use the orm.with_polymorphic() standalone function (Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)This is a legacy method which is replaced by the
with_polymorphic()
function.Warning
The
Query.with_polymorphic()
method does not support 1.4/2.0 style features includingwith_loader_criteria()
. Please migrate code to usewith_polymorphic()
.Query.with_polymorphic()
applies transformations to the “main” mapped class represented by thisQuery
. The “main” mapped class here means theQuery
object’s first argument is a full class, i.e.session.query(SomeClass)
. These transformations allow additional tables to be present in the FROM clause so that columns for a joined-inheritance subclass are available in the query, both for the purposes of load-time efficiency as well as the ability to use these columns at query time.See also
Using with_polymorphic - illustrates current patterns
-
method
sqlalchemy.orm.Query.
with_session(session)¶ Return a
Query
that will use the givenSession
.While the
Query
object is normally instantiated using theSession.query()
method, it is legal to build theQuery
directly without necessarily using aSession
. Such aQuery
object, or anyQuery
already associated with a differentSession
, can produce a newQuery
object associated with a target session using this method:from sqlalchemy.orm import Query query = Query([MyClass]).filter(MyClass.id == 5) result = query.with_session(my_session).one()
-
method
sqlalchemy.orm.Query.
with_statement_hint(text, dialect_name='*')¶ inherited from the
HasHints.with_statement_hint()
method ofHasHints
Add a statement hint to this
Select
or other selectable object.This method is similar to
Select.with_hint()
except that it does not require an individual table, and instead applies to the statement as a whole.Hints here are specific to the backend database and may include directives such as isolation levels, file directives, fetch directives, etc.
New in version 1.0.0.
See also
Select.prefix_with()
- generic SELECT prefixing which also can suit some database-specific HINT syntaxes such as MySQL optimizer hints
-
method
sqlalchemy.orm.Query.
with_transformation(fn)¶ Return a new
Query
object transformed by the given function.E.g.:
def filter_something(criterion): def transform(q): return q.filter(criterion) return transform q = q.with_transformation(filter_something(x==5))
This allows ad-hoc recipes to be created for
Query
objects. See the example at Building Transformers.
-
method
sqlalchemy.orm.Query.
yield_per(count)¶ Yield only
count
rows at a time.The purpose of this method is when fetching very large result sets (> 10K rows), to batch results in sub-collections and yield them out partially, so that the Python interpreter doesn’t need to declare very large areas of memory which is both time consuming and leads to excessive memory use. The performance from fetching hundreds of thousands of rows can often double when a suitable yield-per setting (e.g. approximately 1000) is used, even with DBAPIs that buffer rows (which are most).
As of SQLAlchemy 1.4, the
Query.yield_per()
method is equivalent to using theyield_per
execution option at the ORM level. See the section Fetching Large Result Sets with Yield Per for further background on this option.
-
method
ORM-Specific Query Constructs¶
Object Name | Description |
---|---|
aliased(element[, alias, name, flat, ...]) |
Produce an alias of the given element, usually an |
Represents an “aliased” form of a mapped class for usage with Query. |
|
Provide an inspection interface for an
|
|
A grouping of SQL expressions that are returned by a |
|
join(left, right[, onclause, isouter, ...]) |
Produce an inner join between left and right clauses. |
outerjoin(left, right[, onclause, full, ...]) |
Produce a left outer join between left and right clauses. |
with_loader_criteria(entity_or_base, where_criteria[, loader_only, include_aliases, ...]) |
Add additional WHERE criteria to the load for all occurrences of a particular entity. |
with_parent(instance, prop[, from_entity]) |
Create filtering criterion that relates this query’s primary entity
to the given related instance, using established
|
- function sqlalchemy.orm.aliased(element, alias=None, name=None, flat=False, adapt_on_names=False)¶
Produce an alias of the given element, usually an
AliasedClass
instance.E.g.:
my_alias = aliased(MyClass) session.query(MyClass, my_alias).filter(MyClass.id > my_alias.id)
The
aliased()
function is used to create an ad-hoc mapping of a mapped class to a new selectable. By default, a selectable is generated from the normally mapped selectable (typically aTable
) using theFromClause.alias()
method. However,aliased()
can also be used to link the class to a newselect()
statement. Also, thewith_polymorphic()
function is a variant ofaliased()
that is intended to specify a so-called “polymorphic selectable”, that corresponds to the union of several joined-inheritance subclasses at once.For convenience, the
aliased()
function also accepts plainFromClause
constructs, such as aTable
orselect()
construct. In those cases, theFromClause.alias()
method is called on the object and the newAlias
object returned. The returnedAlias
is not ORM-mapped in this case.See also
ORM Entity Aliases - in the SQLAlchemy 1.4 / 2.0 Tutorial
Selecting ORM Aliases - in the ORM Querying Guide
- Parameters:
element¶ – element to be aliased. Is normally a mapped class, but for convenience can also be a
FromClause
element.alias¶ – Optional selectable unit to map the element to. This is usually used to link the object to a subquery, and should be an aliased select construct as one would produce from the
Query.subquery()
method or theSelect.subquery()
orSelect.alias()
methods of theselect()
construct.name¶ – optional string name to use for the alias, if not specified by the
alias
parameter. The name, among other things, forms the attribute name that will be accessible via tuples returned by aQuery
object. Not supported when creating aliases ofJoin
objects.flat¶ – Boolean, will be passed through to the
FromClause.alias()
call so that aliases ofJoin
objects will alias the individual tables inside the join, rather than creating a subquery. This is generally supported by all modern databases with regards to right-nested joins and generally produces more efficient queries.adapt_on_names¶ –
if True, more liberal “matching” will be used when mapping the mapped columns of the ORM entity to those of the given selectable - a name-based match will be performed if the given selectable doesn’t otherwise have a column that corresponds to one on the entity. The use case for this is when associating an entity with some derived selectable such as one that uses aggregate functions:
class UnitPrice(Base): __tablename__ = 'unit_price' ... unit_id = Column(Integer) price = Column(Numeric) aggregated_unit_price = Session.query( func.sum(UnitPrice.price).label('price') ).group_by(UnitPrice.unit_id).subquery() aggregated_unit_price = aliased(UnitPrice, alias=aggregated_unit_price, adapt_on_names=True)
Above, functions on
aggregated_unit_price
which refer to.price
will return thefunc.sum(UnitPrice.price).label('price')
column, as it is matched on the name “price”. Ordinarily, the “price” function wouldn’t have any “column correspondence” to the actualUnitPrice.price
column as it is not a proxy of the original.
- class sqlalchemy.orm.util.AliasedClass(mapped_class_or_ac, alias=None, name=None, flat=False, adapt_on_names=False, with_polymorphic_mappers=(), with_polymorphic_discriminator=None, base_alias=None, use_mapper_path=False, represents_outer_join=False)¶
Represents an “aliased” form of a mapped class for usage with Query.
The ORM equivalent of a
alias()
construct, this object mimics the mapped class using a__getattr__
scheme and maintains a reference to a realAlias
object.A primary purpose of
AliasedClass
is to serve as an alternate within a SQL statement generated by the ORM, such that an existing mapped entity can be used in multiple contexts. A simple example:# find all pairs of users with the same name user_alias = aliased(User) session.query(User, user_alias).\ join((user_alias, User.id > user_alias.id)).\ filter(User.name == user_alias.name)
AliasedClass
is also capable of mapping an existing mapped class to an entirely new selectable, provided this selectable is column- compatible with the existing mapped selectable, and it can also be configured in a mapping as the target of arelationship()
. See the links below for examples.The
AliasedClass
object is constructed typically using thealiased()
function. It also is produced with additional configuration when using thewith_polymorphic()
function.The resulting object is an instance of
AliasedClass
. This object implements an attribute scheme which produces the same attribute and method interface as the original mapped class, allowingAliasedClass
to be compatible with any attribute technique which works on the original class, including hybrid attributes (see Hybrid Attributes).The
AliasedClass
can be inspected for its underlyingMapper
, aliased selectable, and other information usinginspect()
:from sqlalchemy import inspect my_alias = aliased(MyClass) insp = inspect(my_alias)
The resulting inspection object is an instance of
AliasedInsp
.
- class sqlalchemy.orm.util.AliasedInsp(entity, inspected, selectable, name, with_polymorphic_mappers, polymorphic_on, _base_alias, _use_mapper_path, adapt_on_names, represents_outer_join, nest_adapters)¶
Provide an inspection interface for an
AliasedClass
object.The
AliasedInsp
object is returned given anAliasedClass
using theinspect()
function:from sqlalchemy import inspect from sqlalchemy.orm import aliased my_alias = aliased(MyMappedClass) insp = inspect(my_alias)
Attributes on
AliasedInsp
include:entity
- theAliasedClass
represented.mapper
- theMapper
mapping the underlying class.selectable
- theAlias
construct which ultimately represents an aliasedTable
orSelect
construct.name
- the name of the alias. Also is used as the attribute name when returned in a result tuple fromQuery
.with_polymorphic_mappers
- collection ofMapper
objects indicating all those mappers expressed in the select construct for theAliasedClass
.polymorphic_on
- an alternate column or SQL expression which will be used as the “discriminator” for a polymorphic load.
See also
Class signature
class
sqlalchemy.orm.AliasedInsp
(sqlalchemy.orm.ORMEntityColumnsClauseRole
,sqlalchemy.orm.ORMFromClauseRole
,sqlalchemy.sql.traversals.MemoizedHasCacheKey
,sqlalchemy.orm.base.InspectionAttr
)
- class sqlalchemy.orm.Bundle(name, *exprs, **kw)¶
A grouping of SQL expressions that are returned by a
Query
under one namespace.The
Bundle
essentially allows nesting of the tuple-based results returned by a column-orientedQuery
object. It also is extensible via simple subclassing, where the primary capability to override is that of how the set of expressions should be returned, allowing post-processing as well as custom return types, without involving ORM identity-mapped classes.New in version 0.9.0.
See also
Members
__init__(), c, columns, create_row_processor(), is_aliased_class, is_bundle, is_clause_element, is_mapper, label(), single_entity
Class signature
class
sqlalchemy.orm.Bundle
(sqlalchemy.orm.ORMColumnsClauseRole
,sqlalchemy.sql.annotation.SupportsCloneAnnotations
,sqlalchemy.sql.traversals.MemoizedHasCacheKey
,sqlalchemy.orm.base.InspectionAttr
)-
method
sqlalchemy.orm.Bundle.
__init__(name, *exprs, **kw)¶ Construct a new
Bundle
.e.g.:
bn = Bundle("mybundle", MyClass.x, MyClass.y) for row in session.query(bn).filter( bn.c.x == 5).filter(bn.c.y == 4): print(row.mybundle.x, row.mybundle.y)
-
attribute
sqlalchemy.orm.Bundle.
c = None¶ An alias for
Bundle.columns
.
-
attribute
sqlalchemy.orm.Bundle.
columns = None¶ A namespace of SQL expressions referred to by this
Bundle
.e.g.:
bn = Bundle("mybundle", MyClass.x, MyClass.y) q = sess.query(bn).filter(bn.c.x == 5)
Nesting of bundles is also supported:
b1 = Bundle("b1", Bundle('b2', MyClass.a, MyClass.b), Bundle('b3', MyClass.x, MyClass.y) ) q = sess.query(b1).filter( b1.c.b2.c.a == 5).filter(b1.c.b3.c.y == 9)
See also
-
method
sqlalchemy.orm.Bundle.
create_row_processor(query, procs, labels)¶ Produce the “row processing” function for this
Bundle
.May be overridden by subclasses.
See also
Column Bundles - includes an example of subclassing.
-
attribute
sqlalchemy.orm.Bundle.
is_aliased_class = False¶ True if this object is an instance of
AliasedClass
.
-
attribute
sqlalchemy.orm.Bundle.
is_bundle = True¶ True if this object is an instance of
Bundle
.
-
attribute
sqlalchemy.orm.Bundle.
is_clause_element = False¶ True if this object is an instance of
ClauseElement
.
-
attribute
sqlalchemy.orm.Bundle.
is_mapper = False¶ True if this object is an instance of
Mapper
.
-
method
sqlalchemy.orm.Bundle.
label(name)¶ Provide a copy of this
Bundle
passing a new label.
-
attribute
sqlalchemy.orm.Bundle.
single_entity = False¶ If True, queries for a single Bundle will be returned as a single entity, rather than an element within a keyed tuple.
-
method
- class sqlalchemy.orm.Load(entity)
Represents loader options which modify the state of a
Query
in order to affect how various mapped attributes are loaded.The
Load
object is in most cases used implicitly behind the scenes when one makes use of a query option likejoinedload()
,defer()
, or similar. However, theLoad
object can also be used directly, and in some cases can be useful.To use
Load
directly, instantiate it with the target mapped class as the argument. This style of usage is useful when dealing with aQuery
that has multiple entities:myopt = Load(MyClass).joinedload("widgets")
The above
myopt
can now be used withQuery.options()
, where it will only take effect for theMyClass
entity:session.query(MyClass, MyOtherClass).options(myopt)
One case where
Load
is useful as public API is when specifying “wildcard” options that only take effect for a certain class:session.query(Order).options(Load(Order).lazyload('*'))
Above, all relationships on
Order
will be lazy-loaded, but other attributes on those descendant objects will load using their normal loader strategy.Class signature
class
sqlalchemy.orm.Load
(sqlalchemy.sql.expression.Generative
,sqlalchemy.orm.LoaderOption
)-
method
sqlalchemy.orm.Load.
baked_lazyload(attr) Produce a new
Load
object with thebaked_lazyload()
option applied.See
baked_lazyload()
for usage examples.
-
method
sqlalchemy.orm.Load.
contains_eager(attr, alias=None) Produce a new
Load
object with thecontains_eager()
option applied.See
contains_eager()
for usage examples.
-
method
sqlalchemy.orm.Load.
defaultload(attr) Produce a new
Load
object with thedefaultload()
option applied.See
defaultload()
for usage examples.
-
method
sqlalchemy.orm.Load.
defer(key, raiseload=False) Produce a new
Load
object with thedefer()
option applied.See
defer()
for usage examples.
-
method
sqlalchemy.orm.Load.
immediateload(attr) Produce a new
Load
object with theimmediateload()
option applied.See
immediateload()
for usage examples.
-
method
sqlalchemy.orm.Load.
joinedload(attr, innerjoin=None) Produce a new
Load
object with thejoinedload()
option applied.See
joinedload()
for usage examples.
-
method
sqlalchemy.orm.Load.
lazyload(attr) Produce a new
Load
object with thelazyload()
option applied.See
lazyload()
for usage examples.
-
method
sqlalchemy.orm.Load.
load_only(*attrs) Produce a new
Load
object with theload_only()
option applied.See
load_only()
for usage examples.
-
method
sqlalchemy.orm.Load.
noload(attr) Produce a new
Load
object with thenoload()
option applied.See
noload()
for usage examples.
-
method
sqlalchemy.orm.Load.
options(*opts) Apply a series of options as sub-options to this
Load
object.E.g.:
query = session.query(Author) query = query.options( joinedload(Author.book).options( load_only(Book.summary, Book.excerpt), joinedload(Book.citations).options( joinedload(Citation.author) ) ) )
- Parameters:
*opts¶ – A series of loader option objects (ultimately
Load
objects) which should be applied to the path specified by thisLoad
object.
New in version 1.3.6.
-
method
sqlalchemy.orm.Load.
process_compile_state(compile_state) Apply a modification to a given
CompileState
.
-
method
sqlalchemy.orm.Load.
process_compile_state_replaced_entities(compile_state, mapper_entities) Apply a modification to a given
CompileState
, given entities that were replaced by with_only_columns() or with_entities().New in version 1.4.19.
-
attribute
sqlalchemy.orm.Load.
propagate_to_loaders = False if True, indicate this option should be carried along to “secondary” SELECT statements that occur for relationship lazy loaders as well as attribute load / refresh operations.
-
method
sqlalchemy.orm.Load.
raiseload(attr, sql_only=False) Produce a new
Load
object with theraiseload()
option applied.See
raiseload()
for usage examples.
-
method
sqlalchemy.orm.Load.
selectin_polymorphic(classes) Produce a new
Load
object with theselectin_polymorphic()
option applied.See
selectin_polymorphic()
for usage examples.
-
method
sqlalchemy.orm.Load.
selectinload(attr) Produce a new
Load
object with theselectinload()
option applied.See
selectinload()
for usage examples.
-
method
sqlalchemy.orm.Load.
subqueryload(attr) Produce a new
Load
object with thesubqueryload()
option applied.See
subqueryload()
for usage examples.
-
method
sqlalchemy.orm.Load.
undefer(key) Produce a new
Load
object with theundefer()
option applied.See
undefer()
for usage examples.
-
method
sqlalchemy.orm.Load.
undefer_group(name) Produce a new
Load
object with theundefer_group()
option applied.See
undefer_group()
for usage examples.
-
method
sqlalchemy.orm.Load.
with_expression(key, expression) Produce a new
Load
object with thewith_expression()
option applied.See
with_expression()
for usage examples.
-
method
- function sqlalchemy.orm.with_loader_criteria(entity_or_base, where_criteria, loader_only=False, include_aliases=False, propagate_to_loaders=True, track_closure_variables=True)¶
Add additional WHERE criteria to the load for all occurrences of a particular entity.
New in version 1.4.
The
with_loader_criteria()
option is intended to add limiting criteria to a particular kind of entity in a query, globally, meaning it will apply to the entity as it appears in the SELECT query as well as within any subqueries, join conditions, and relationship loads, including both eager and lazy loaders, without the need for it to be specified in any particular part of the query. The rendering logic uses the same system used by single table inheritance to ensure a certain discriminator is applied to a table.E.g., using 2.0-style queries, we can limit the way the
User.addresses
collection is loaded, regardless of the kind of loading used:from sqlalchemy.orm import with_loader_criteria stmt = select(User).options( selectinload(User.addresses), with_loader_criteria(Address, Address.email_address != 'foo')) )
Above, the “selectinload” for
User.addresses
will apply the given filtering criteria to the WHERE clause.Another example, where the filtering will be applied to the ON clause of the join, in this example using 1.x style queries:
q = session.query(User).outerjoin(User.addresses).options( with_loader_criteria(Address, Address.email_address != 'foo')) )
The primary purpose of
with_loader_criteria()
is to use it in theSessionEvents.do_orm_execute()
event handler to ensure that all occurrences of a particular entity are filtered in a certain way, such as filtering for access control roles. It also can be used to apply criteria to relationship loads. In the example below, we can apply a certain set of rules to all queries emitted by a particularSession
:session = Session(bind=engine) @event.listens_for("do_orm_execute", session) def _add_filtering_criteria(execute_state): if ( execute_state.is_select and not execute_state.is_column_load and not execute_state.is_relationship_load ): execute_state.statement = execute_state.statement.options( with_loader_criteria( SecurityRole, lambda cls: cls.role.in_(['some_role']), include_aliases=True ) )
In the above example, the
SessionEvents.do_orm_execute()
event will intercept all queries emitted using theSession
. For those queries which are SELECT statements and are not attribute or relationship loads a customwith_loader_criteria()
option is added to the query. Thewith_loader_criteria()
option will be used in the given statement and will also be automatically propagated to all relationship loads that descend from this query.The criteria argument given is a
lambda
that accepts acls
argument. The given class will expand to include all mapped subclass and need not itself be a mapped class.Tip
When using
with_loader_criteria()
option in conjunction with thecontains_eager()
loader option, it’s important to note thatwith_loader_criteria()
only affects the part of the query that determines what SQL is rendered in terms of the WHERE and FROM clauses. Thecontains_eager()
option does not affect the rendering of the SELECT statement outside of the columns clause, so does not have any interaction with thewith_loader_criteria()
option. However, the way things “work” is thatcontains_eager()
is meant to be used with a query that is already selecting from the additional entities in some way, wherewith_loader_criteria()
can apply it’s additional criteria.In the example below, assuming a mapping relationship as
A -> A.bs -> B
, the givenwith_loader_criteria()
option will affect the way in which the JOIN is rendered:stmt = select(A).join(A.bs).options( contains_eager(A.bs), with_loader_criteria(B, B.flag == 1) )
Above, the given
with_loader_criteria()
option will affect the ON clause of the JOIN that is specified by.join(A.bs)
, so is applied as expected. Thecontains_eager()
option has the effect that columns fromB
are added to the columns clause:SELECT b.id, b.a_id, b.data, b.flag, a.id AS id_1, a.data AS data_1 FROM a JOIN b ON a.id = b.a_id AND b.flag = :flag_1
The use of the
contains_eager()
option within the above statement has no effect on the behavior of thewith_loader_criteria()
option. If thecontains_eager()
option were omitted, the SQL would be the same as regards the FROM and WHERE clauses, wherewith_loader_criteria()
continues to add its criteria to the ON clause of the JOIN. The addition ofcontains_eager()
only affects the columns clause, in that additional columns againstb
are added which are then consumed by the ORM to produceB
instances.Warning
The use of a lambda inside of the call to
with_loader_criteria()
is only invoked once per unique class. Custom functions should not be invoked within this lambda. See Using Lambdas to add significant speed gains to statement production for an overview of the “lambda SQL” feature, which is for advanced use only.- Parameters:
entity_or_base¶ – a mapped class, or a class that is a super class of a particular set of mapped classes, to which the rule will apply.
where_criteria¶ –
a Core SQL expression that applies limiting criteria. This may also be a “lambda:” or Python function that accepts a target class as an argument, when the given class is a base with many different mapped subclasses.
Note
To support pickling, use a module-level Python function to produce the SQL expression instead of a lambda or a fixed SQL expression, which tend to not be picklable.
include_aliases¶ – if True, apply the rule to
aliased()
constructs as well.propagate_to_loaders¶ – defaults to True, apply to relationship loaders such as lazy loaders. This indicates that the option object itself including SQL expression is carried along with each loaded instance. Set to
False
to prevent the object from being assigned to individual instances.
See also
ORM Query Events - includes examples of using
with_loader_criteria()
.Adding global WHERE / ON criteria - basic example on how to combine
with_loader_criteria()
with theSessionEvents.do_orm_execute()
event.- Parameters:
track_closure_variables¶ –
when False, closure variables inside of a lambda expression will not be used as part of any cache key. This allows more complex expressions to be used inside of a lambda expression but requires that the lambda ensures it returns the identical SQL every time given a particular class.
New in version 1.4.0b2.
- function sqlalchemy.orm.join(left, right, onclause=None, isouter=False, full=False, join_to_left=None)¶
Produce an inner join between left and right clauses.
join()
is an extension to the core join interface provided byjoin()
, where the left and right selectables may be not only core selectable objects such asTable
, but also mapped classes orAliasedClass
instances. The “on” clause can be a SQL expression or an ORM mapped attribute referencing a configuredrelationship()
.Deprecated since version 1.4: using a string relationship name for the “onclause” is deprecated and will be removed in 2.0; the onclause may be only an ORM-mapped relationship attribute or a SQL expression construct.
join()
is not commonly needed in modern usage, as its functionality is encapsulated within that of theSelect.join()
andQuery.join()
methods. which feature a significant amount of automation beyondjoin()
by itself. Explicit use ofjoin()
with ORM-enabled SELECT statements involves use of theSelect.select_from()
method, as in:from sqlalchemy.orm import join stmt = select(User).\ select_from(join(User, Address, User.addresses)).\ filter(Address.email_address=='foo@bar.com')
In modern SQLAlchemy the above join can be written more succinctly as:
stmt = select(User).\ join(User.addresses).\ filter(Address.email_address=='foo@bar.com')
Warning
using
join()
directly may not work properly with modern ORM options such aswith_loader_criteria()
. It is strongly recommended to use the idiomatic join patterns provided by methods such asSelect.join()
andSelect.join_from()
when creating ORM joins.See also
Joins - in the ORM Querying Guide for background on idiomatic ORM join patterns
- function sqlalchemy.orm.outerjoin(left, right, onclause=None, full=False, join_to_left=None)¶
Produce a left outer join between left and right clauses.
This is the “outer join” version of the
join()
function, featuring the same behavior except that an OUTER JOIN is generated. See that function’s documentation for other usage details.
- function sqlalchemy.orm.with_parent(instance, prop, from_entity=None)¶
Create filtering criterion that relates this query’s primary entity to the given related instance, using established
relationship()
configuration.E.g.:
stmt = select(Address).where(with_parent(some_user, User.addresses))
The SQL rendered is the same as that rendered when a lazy loader would fire off from the given parent on that attribute, meaning that the appropriate state is taken from the parent object in Python without the need to render joins to the parent table in the rendered statement.
The given property may also make use of
PropComparator.of_type()
to indicate the left side of the criteria:a1 = aliased(Address) a2 = aliased(Address) stmt = select(a1, a2).where( with_parent(u1, User.addresses.of_type(a2)) )
The above use is equivalent to using the
from_entity()
argument:a1 = aliased(Address) a2 = aliased(Address) stmt = select(a1, a2).where( with_parent(u1, User.addresses, from_entity=a2) )
- Parameters:
instance¶ – An instance which has some
relationship()
.property¶ –
String property name, or class-bound attribute, which indicates what relationship from the instance should be used to reconcile the parent/child relationship.
Deprecated since version 1.4: Using strings is deprecated and will be removed in SQLAlchemy 2.0. Please use the class-bound attribute directly.
from_entity¶ –
Entity in which to consider as the left side. This defaults to the “zero” entity of the
Query
itself.New in version 1.2.
flambé! the dragon and The Alchemist image designs created and generously donated by Rotem Yaari.
Created using Sphinx 7.2.6. Documentation last generated: Thu 10 Oct 2024 04:49:33 PM EDT