SQLAlchemy 0.8 Documentation
Support for the Firebird database.
The following dialect/DBAPI options are available. Please refer to individual DBAPI sections for connect information.
Firebird offers two distinct dialects (not to be confused with a SQLAlchemy Dialect):
- dialect 1
- This is the old syntax and behaviour, inherited from Interbase pre-6.0.
- dialect 3
- This is the newer and supported syntax, introduced in Interbase 6.0.
The SQLAlchemy Firebird dialect detects these versions and adjusts its representation of SQL accordingly. However, support for dialect 1 is not well tested and probably has incompatibilities.
Firebird locks tables aggressively. For this reason, a DROP TABLE may hang until other transactions are released. SQLAlchemy does its best to release transactions as quickly as possible. The most common cause of hanging transactions is a non-fully consumed result set, i.e.:
result = engine.execute("select * from table") row = result.fetchone() return
Where above, the ResultProxy has not been fully consumed. The connection will be returned to the pool and the transactional state rolled back once the Python garbage collector reclaims the objects which hold onto the connection, which often occurs asynchronously. The above use case can be alleviated by calling first() on the ResultProxy which will fetch the first row and immediately close all remaining cursor/connection resources.
Firebird 2.0 supports returning a result set from inserts, and 2.1 extends that to deletes and updates. This is generically exposed by the SQLAlchemy returning() method, such as:
# INSERT..RETURNING result = table.insert().returning(table.c.col1, table.c.col2).\ values(name='foo') print result.fetchall() # UPDATE..RETURNING raises = empl.update().returning(empl.c.id, empl.c.salary).\ where(empl.c.sales>100).\ values(dict(salary=empl.c.salary * 1.1)) print raises.fetchall()
Support for the Firebird database via the kinterbasdb driver.
Documentation and download information (if applicable) for kinterbasdb is available at: http://firebirdsql.org/index.php?op=devel&sub=python
The Kinterbasdb backend accepts the enable_rowcount and retaining arguments accepted by the sqlalchemy.dialects.firebird.fdb dialect. In addition, it also accepts the following:
- type_conv - select the kind of mapping done on the types: by default SQLAlchemy uses 200 with Unicode, datetime and decimal support. See the linked documents below for further information.
- concurrency_level - set the backend policy with regards to threading issues: by default SQLAlchemy uses policy 1. See the linked documents below for futher information.
Support for the Firebird database via the fdb driver.
fdb is a kinterbasdb compatible DBAPI for Firebird.
New in version 0.8: - Support for the fdb Firebird driver.
Documentation and download information (if applicable) for fdb is available at: http://pypi.python.org/pypi/fdb/
The fdb dialect is new and not yet tested (can’t get fdb to build).
The fdb dialect is based on the sqlalchemy.dialects.firebird.kinterbasdb dialect, however does not accept every argument that Kinterbasdb does.
enable_rowcount - True by default, setting this to False disables the usage of “cursor.rowcount” with the Kinterbasdb dialect, which SQLAlchemy ordinarily calls upon automatically after any UPDATE or DELETE statement. When disabled, SQLAlchemy’s ResultProxy will return -1 for result.rowcount. The rationale here is that Kinterbasdb requires a second round trip to the database when .rowcount is called - since SQLA’s resultproxy automatically closes the cursor after a non-result-returning statement, rowcount must be called, if at all, before the result object is returned. Additionally, cursor.rowcount may not return correct results with older versions of Firebird, and setting this flag to False will also cause the SQLAlchemy ORM to ignore its usage. The behavior can also be controlled on a per-execution basis using the enable_rowcount option with Connection.execution_options():
conn = engine.connect().execution_options(enable_rowcount=True) r = conn.execute(stmt) print r.rowcount
retaining - True by default. Leaving this on True will pass the retaining=True keyword argument to the .commit() and .rollback() methods of the DBAPI connection, which can improve performance in some situations, but apparently with significant caveats. Please read the fdb and/or kinterbasdb DBAPI documentation in order to understand the implications of this flag.
New in version 0.8.2: - retaining keyword argument specifying transaction retaining behavior. This flag will default to False in 0.9.
http://pythonhosted.org/fdb/usage-guide.html#retaining-transactions - information on the “retaining” flag.