SQLAlchemy 1.3 Documentation
SQLAlchemy Core
- SQL Expression Language Tutorial
- SQL Statements and Expressions API
- Schema Definition Language
- Column and Data Types
- Engine and Connection Use
- Engine Configuration
- Working with Engines and Connections
- Connection Pooling
- Core Events¶
Events
- Connection Pool Events
- SQL Execution and Connection Events
ConnectionEvents
ConnectionEvents.after_cursor_execute()
ConnectionEvents.after_execute()
ConnectionEvents.before_cursor_execute()
ConnectionEvents.before_execute()
ConnectionEvents.begin()
ConnectionEvents.begin_twophase()
ConnectionEvents.commit()
ConnectionEvents.commit_twophase()
ConnectionEvents.dbapi_error()
ConnectionEvents.engine_connect()
ConnectionEvents.engine_disposed()
ConnectionEvents.handle_error()
ConnectionEvents.prepare_twophase()
ConnectionEvents.release_savepoint()
ConnectionEvents.rollback()
ConnectionEvents.rollback_savepoint()
ConnectionEvents.rollback_twophase()
ConnectionEvents.savepoint()
ConnectionEvents.set_connection_execution_options()
ConnectionEvents.set_engine_execution_options()
DialectEvents
- Schema Events
- Core API Basics
Project Versions
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- Next: Core API Basics
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- Core Events
Events
- Connection Pool Events
- SQL Execution and Connection Events
ConnectionEvents
ConnectionEvents.after_cursor_execute()
ConnectionEvents.after_execute()
ConnectionEvents.before_cursor_execute()
ConnectionEvents.before_execute()
ConnectionEvents.begin()
ConnectionEvents.begin_twophase()
ConnectionEvents.commit()
ConnectionEvents.commit_twophase()
ConnectionEvents.dbapi_error()
ConnectionEvents.engine_connect()
ConnectionEvents.engine_disposed()
ConnectionEvents.handle_error()
ConnectionEvents.prepare_twophase()
ConnectionEvents.release_savepoint()
ConnectionEvents.rollback()
ConnectionEvents.rollback_savepoint()
ConnectionEvents.rollback_twophase()
ConnectionEvents.savepoint()
ConnectionEvents.set_connection_execution_options()
ConnectionEvents.set_engine_execution_options()
DialectEvents
- Schema Events
Core Events¶
This section describes the event interfaces provided in SQLAlchemy Core. For an introduction to the event listening API, see Events. ORM events are described in ORM Events.
Object Name | Description |
---|---|
Define event listening functions for a particular target type. |
- class sqlalchemy.event.base.Events¶
Define event listening functions for a particular target type.
Connection Pool Events¶
Object Name | Description |
---|---|
Available events for |
- class sqlalchemy.events.PoolEvents¶
Available events for
Pool
.The methods here define the name of an event as well as the names of members that are passed to listener functions.
e.g.:
from sqlalchemy import event def my_on_checkout(dbapi_conn, connection_rec, connection_proxy): "handle an on checkout event" event.listen(Pool, 'checkout', my_on_checkout)
In addition to accepting the
Pool
class andPool
instances,PoolEvents
also acceptsEngine
objects and theEngine
class as targets, which will be resolved to the.pool
attribute of the given engine or thePool
class:engine = create_engine("postgresql://scott:tiger@localhost/test") # will associate with engine.pool event.listen(engine, 'checkout', my_on_checkout)
Members
checkin(), checkout(), close(), close_detached(), connect(), detach(), first_connect(), invalidate(), reset(), soft_invalidate()
Class signature
class
sqlalchemy.events.PoolEvents
(sqlalchemy.event.Events
)-
method
sqlalchemy.events.PoolEvents.
checkin(dbapi_connection, connection_record)¶ Called when a connection returns to the pool.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngineOrPool, 'checkin') def receive_checkin(dbapi_connection, connection_record): "listen for the 'checkin' event" # ... (event handling logic) ...
Note that the connection may be closed, and may be None if the connection has been invalidated.
checkin
will not be called for detached connections. (They do not return to the pool.)- Parameters:
dbapi_connection¶ – a DBAPI connection.
connection_record¶ – the
_ConnectionRecord
managing the DBAPI connection.
-
method
sqlalchemy.events.PoolEvents.
checkout(dbapi_connection, connection_record, connection_proxy)¶ Called when a connection is retrieved from the Pool.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngineOrPool, 'checkout') def receive_checkout(dbapi_connection, connection_record, connection_proxy): "listen for the 'checkout' event" # ... (event handling logic) ...
- Parameters:
dbapi_connection¶ – a DBAPI connection.
connection_record¶ – the
_ConnectionRecord
managing the DBAPI connection.connection_proxy¶ – the
_ConnectionFairy
object which will proxy the public interface of the DBAPI connection for the lifespan of the checkout.
If you raise a
DisconnectionError
, the current connection will be disposed and a fresh connection retrieved. Processing of all checkout listeners will abort and restart using the new connection.See also
ConnectionEvents.engine_connect()
- a similar event which occurs upon creation of a newConnection
.
-
method
sqlalchemy.events.PoolEvents.
close(dbapi_connection, connection_record)¶ Called when a DBAPI connection is closed.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngineOrPool, 'close') def receive_close(dbapi_connection, connection_record): "listen for the 'close' event" # ... (event handling logic) ...
The event is emitted before the close occurs.
The close of a connection can fail; typically this is because the connection is already closed. If the close operation fails, the connection is discarded.
The
close()
event corresponds to a connection that’s still associated with the pool. To intercept close events for detached connections useclose_detached()
.New in version 1.1.
-
method
sqlalchemy.events.PoolEvents.
close_detached(dbapi_connection)¶ Called when a detached DBAPI connection is closed.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngineOrPool, 'close_detached') def receive_close_detached(dbapi_connection): "listen for the 'close_detached' event" # ... (event handling logic) ...
The event is emitted before the close occurs.
The close of a connection can fail; typically this is because the connection is already closed. If the close operation fails, the connection is discarded.
New in version 1.1.
-
method
sqlalchemy.events.PoolEvents.
connect(dbapi_connection, connection_record)¶ Called at the moment a particular DBAPI connection is first created for a given
Pool
.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngineOrPool, 'connect') def receive_connect(dbapi_connection, connection_record): "listen for the 'connect' event" # ... (event handling logic) ...
This event allows one to capture the point directly after which the DBAPI module-level
.connect()
method has been used in order to produce a new DBAPI connection.- Parameters:
dbapi_connection¶ – a DBAPI connection.
connection_record¶ – the
_ConnectionRecord
managing the DBAPI connection.
-
method
sqlalchemy.events.PoolEvents.
detach(dbapi_connection, connection_record)¶ Called when a DBAPI connection is “detached” from a pool.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngineOrPool, 'detach') def receive_detach(dbapi_connection, connection_record): "listen for the 'detach' event" # ... (event handling logic) ...
This event is emitted after the detach occurs. The connection is no longer associated with the given connection record.
New in version 1.1.
-
method
sqlalchemy.events.PoolEvents.
first_connect(dbapi_connection, connection_record)¶ Called exactly once for the first time a DBAPI connection is checked out from a particular
Pool
.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngineOrPool, 'first_connect') def receive_first_connect(dbapi_connection, connection_record): "listen for the 'first_connect' event" # ... (event handling logic) ...
The rationale for
PoolEvents.first_connect()
is to determine information about a particular series of database connections based on the settings used for all connections. Since a particularPool
refers to a single “creator” function (which in terms of aEngine
refers to the URL and connection options used), it is typically valid to make observations about a single connection that can be safely assumed to be valid about all subsequent connections, such as the database version, the server and client encoding settings, collation settings, and many others.- Parameters:
dbapi_connection¶ – a DBAPI connection.
connection_record¶ – the
_ConnectionRecord
managing the DBAPI connection.
-
method
sqlalchemy.events.PoolEvents.
invalidate(dbapi_connection, connection_record, exception)¶ Called when a DBAPI connection is to be “invalidated”.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngineOrPool, 'invalidate') def receive_invalidate(dbapi_connection, connection_record, exception): "listen for the 'invalidate' event" # ... (event handling logic) ...
This event is called any time the
_ConnectionRecord.invalidate()
method is invoked, either from API usage or via “auto-invalidation”, without thesoft
flag.The event occurs before a final attempt to call
.close()
on the connection occurs.- Parameters:
dbapi_connection¶ – a DBAPI connection.
connection_record¶ – the
_ConnectionRecord
managing the DBAPI connection.exception¶ – the exception object corresponding to the reason for this invalidation, if any. May be
None
.
New in version 0.9.2: Added support for connection invalidation listening.
See also
-
method
sqlalchemy.events.PoolEvents.
reset(dbapi_connection, connection_record)¶ Called before the “reset” action occurs for a pooled connection.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngineOrPool, 'reset') def receive_reset(dbapi_connection, connection_record): "listen for the 'reset' event" # ... (event handling logic) ...
This event represents when the
rollback()
method is called on the DBAPI connection before it is returned to the pool. The behavior of “reset” can be controlled, including disabled, using thereset_on_return
pool argument.The
PoolEvents.reset()
event is usually followed by thePoolEvents.checkin()
event is called, except in those cases where the connection is discarded immediately after reset.- Parameters:
dbapi_connection¶ – a DBAPI connection.
connection_record¶ – the
_ConnectionRecord
managing the DBAPI connection.
-
method
sqlalchemy.events.PoolEvents.
soft_invalidate(dbapi_connection, connection_record, exception)¶ Called when a DBAPI connection is to be “soft invalidated”.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngineOrPool, 'soft_invalidate') def receive_soft_invalidate(dbapi_connection, connection_record, exception): "listen for the 'soft_invalidate' event" # ... (event handling logic) ...
This event is called any time the
_ConnectionRecord.invalidate()
method is invoked with thesoft
flag.Soft invalidation refers to when the connection record that tracks this connection will force a reconnect after the current connection is checked in. It does not actively close the dbapi_connection at the point at which it is called.
New in version 1.0.3.
-
method
SQL Execution and Connection Events¶
Object Name | Description |
---|---|
Available events for |
|
event interface for execution-replacement functions. |
- class sqlalchemy.events.ConnectionEvents¶
Available events for
Connectable
, which includesConnection
andEngine
.The methods here define the name of an event as well as the names of members that are passed to listener functions.
An event listener can be associated with any
Connectable
class or instance, such as anEngine
, e.g.:from sqlalchemy import event, create_engine def before_cursor_execute(conn, cursor, statement, parameters, context, executemany): log.info("Received statement: %s", statement) engine = create_engine('postgresql://scott:tiger@localhost/test') event.listen(engine, "before_cursor_execute", before_cursor_execute)
or with a specific
Connection
:with engine.begin() as conn: @event.listens_for(conn, 'before_cursor_execute') def before_cursor_execute(conn, cursor, statement, parameters, context, executemany): log.info("Received statement: %s", statement)
When the methods are called with a statement parameter, such as in
after_cursor_execute()
,before_cursor_execute()
anddbapi_error()
, the statement is the exact SQL string that was prepared for transmission to the DBAPIcursor
in the connection’sDialect
.The
before_execute()
andbefore_cursor_execute()
events can also be established with theretval=True
flag, which allows modification of the statement and parameters to be sent to the database. Thebefore_cursor_execute()
event is particularly useful here to add ad-hoc string transformations, such as comments, to all executions:from sqlalchemy.engine import Engine from sqlalchemy import event @event.listens_for(Engine, "before_cursor_execute", retval=True) def comment_sql_calls(conn, cursor, statement, parameters, context, executemany): statement = statement + " -- some comment" return statement, parameters
Note
ConnectionEvents
can be established on any combination ofEngine
,Connection
, as well as instances of each of those classes. Events across all four scopes will fire off for a given instance ofConnection
. However, for performance reasons, theConnection
object determines at instantiation time whether or not its parentEngine
has event listeners established. Event listeners added to theEngine
class or to an instance ofEngine
after the instantiation of a dependentConnection
instance will usually not be available on thatConnection
instance. The newly added listeners will instead take effect forConnection
instances created subsequent to those event listeners being established on the parentEngine
class or instance.- Parameters:
retval=False¶ – Applies to the
before_execute()
andbefore_cursor_execute()
events only. When True, the user-defined event function must have a return value, which is a tuple of parameters that replace the given statement and parameters. See those methods for a description of specific return arguments.
Members
after_cursor_execute(), after_execute(), before_cursor_execute(), before_execute(), begin(), begin_twophase(), commit(), commit_twophase(), dbapi_error(), engine_connect(), engine_disposed(), handle_error(), prepare_twophase(), release_savepoint(), rollback(), rollback_savepoint(), rollback_twophase(), savepoint(), set_connection_execution_options(), set_engine_execution_options()
Class signature
class
sqlalchemy.events.ConnectionEvents
(sqlalchemy.event.Events
)-
method
sqlalchemy.events.ConnectionEvents.
after_cursor_execute(conn, cursor, statement, parameters, context, executemany)¶ Intercept low-level cursor execute() events after execution.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'after_cursor_execute') def receive_after_cursor_execute(conn, cursor, statement, parameters, context, executemany): "listen for the 'after_cursor_execute' event" # ... (event handling logic) ... # named argument style (new in 0.9) @event.listens_for(SomeEngine, 'after_cursor_execute', named=True) def receive_after_cursor_execute(**kw): "listen for the 'after_cursor_execute' event" conn = kw['conn'] cursor = kw['cursor'] # ... (event handling logic) ...
- Parameters:
conn¶ –
Connection
objectcursor¶ – DBAPI cursor object. Will have results pending if the statement was a SELECT, but these should not be consumed as they will be needed by the
ResultProxy
.statement¶ – string SQL statement, as passed to the DBAPI
parameters¶ – Dictionary, tuple, or list of parameters being passed to the
execute()
orexecutemany()
method of the DBAPIcursor
. In some cases may beNone
.context¶ –
ExecutionContext
object in use. May beNone
.executemany¶ – boolean, if
True
, this is anexecutemany()
call, ifFalse
, this is anexecute()
call.
-
method
sqlalchemy.events.ConnectionEvents.
after_execute(conn, clauseelement, multiparams, params, result)¶ Intercept high level execute() events after execute.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'after_execute') def receive_after_execute(conn, clauseelement, multiparams, params, result): "listen for the 'after_execute' event" # ... (event handling logic) ... # named argument style (new in 0.9) @event.listens_for(SomeEngine, 'after_execute', named=True) def receive_after_execute(**kw): "listen for the 'after_execute' event" conn = kw['conn'] clauseelement = kw['clauseelement'] # ... (event handling logic) ...
- Parameters:
conn¶ –
Connection
objectclauseelement¶ – SQL expression construct,
Compiled
instance, or string statement passed toConnection.execute()
.multiparams¶ – Multiple parameter sets, a list of dictionaries.
params¶ – Single parameter set, a single dictionary.
result¶ –
ResultProxy
generated by the execution .
-
method
sqlalchemy.events.ConnectionEvents.
before_cursor_execute(conn, cursor, statement, parameters, context, executemany)¶ Intercept low-level cursor execute() events before execution, receiving the string SQL statement and DBAPI-specific parameter list to be invoked against a cursor.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'before_cursor_execute') def receive_before_cursor_execute(conn, cursor, statement, parameters, context, executemany): "listen for the 'before_cursor_execute' event" # ... (event handling logic) ... # named argument style (new in 0.9) @event.listens_for(SomeEngine, 'before_cursor_execute', named=True) def receive_before_cursor_execute(**kw): "listen for the 'before_cursor_execute' event" conn = kw['conn'] cursor = kw['cursor'] # ... (event handling logic) ...
This event is a good choice for logging as well as late modifications to the SQL string. It’s less ideal for parameter modifications except for those which are specific to a target backend.
This event can be optionally established with the
retval=True
flag. Thestatement
andparameters
arguments should be returned as a two-tuple in this case:@event.listens_for(Engine, "before_cursor_execute", retval=True) def before_cursor_execute(conn, cursor, statement, parameters, context, executemany): # do something with statement, parameters return statement, parameters
See the example at
ConnectionEvents
.- Parameters:
conn¶ –
Connection
objectcursor¶ – DBAPI cursor object
statement¶ – string SQL statement, as to be passed to the DBAPI
parameters¶ – Dictionary, tuple, or list of parameters being passed to the
execute()
orexecutemany()
method of the DBAPIcursor
. In some cases may beNone
.context¶ –
ExecutionContext
object in use. May beNone
.executemany¶ – boolean, if
True
, this is anexecutemany()
call, ifFalse
, this is anexecute()
call.
-
method
sqlalchemy.events.ConnectionEvents.
before_execute(conn, clauseelement, multiparams, params)¶ Intercept high level execute() events, receiving uncompiled SQL constructs and other objects prior to rendering into SQL.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'before_execute') def receive_before_execute(conn, clauseelement, multiparams, params): "listen for the 'before_execute' event" # ... (event handling logic) ... # named argument style (new in 0.9) @event.listens_for(SomeEngine, 'before_execute', named=True) def receive_before_execute(**kw): "listen for the 'before_execute' event" conn = kw['conn'] clauseelement = kw['clauseelement'] # ... (event handling logic) ...
This event is good for debugging SQL compilation issues as well as early manipulation of the parameters being sent to the database, as the parameter lists will be in a consistent format here.
This event can be optionally established with the
retval=True
flag. Theclauseelement
,multiparams
, andparams
arguments should be returned as a three-tuple in this case:@event.listens_for(Engine, "before_execute", retval=True) def before_execute(conn, clauseelement, multiparams, params): # do something with clauseelement, multiparams, params return clauseelement, multiparams, params
- Parameters:
conn¶ –
Connection
objectclauseelement¶ – SQL expression construct,
Compiled
instance, or string statement passed toConnection.execute()
.multiparams¶ – Multiple parameter sets, a list of dictionaries.
params¶ – Single parameter set, a single dictionary.
See also
-
method
sqlalchemy.events.ConnectionEvents.
begin(conn)¶ Intercept begin() events.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'begin') def receive_begin(conn): "listen for the 'begin' event" # ... (event handling logic) ...
- Parameters:
conn¶ –
Connection
object
-
method
sqlalchemy.events.ConnectionEvents.
begin_twophase(conn, xid)¶ Intercept begin_twophase() events.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'begin_twophase') def receive_begin_twophase(conn, xid): "listen for the 'begin_twophase' event" # ... (event handling logic) ...
- Parameters:
conn¶ –
Connection
objectxid¶ – two-phase XID identifier
-
method
sqlalchemy.events.ConnectionEvents.
commit(conn)¶ Intercept commit() events, as initiated by a
Transaction
.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'commit') def receive_commit(conn): "listen for the 'commit' event" # ... (event handling logic) ...
Note that the
Pool
may also “auto-commit” a DBAPI connection upon checkin, if thereset_on_return
flag is set to the value'commit'
. To intercept this commit, use thePoolEvents.reset()
hook.- Parameters:
conn¶ –
Connection
object
-
method
sqlalchemy.events.ConnectionEvents.
commit_twophase(conn, xid, is_prepared)¶ Intercept commit_twophase() events.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'commit_twophase') def receive_commit_twophase(conn, xid, is_prepared): "listen for the 'commit_twophase' event" # ... (event handling logic) ...
- Parameters:
conn¶ –
Connection
objectxid¶ – two-phase XID identifier
is_prepared¶ – boolean, indicates if
TwoPhaseTransaction.prepare()
was called.
-
method
sqlalchemy.events.ConnectionEvents.
dbapi_error(conn, cursor, statement, parameters, context, exception)¶ Intercept a raw DBAPI error.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'dbapi_error') def receive_dbapi_error(conn, cursor, statement, parameters, context, exception): "listen for the 'dbapi_error' event" # ... (event handling logic) ... # named argument style (new in 0.9) @event.listens_for(SomeEngine, 'dbapi_error', named=True) def receive_dbapi_error(**kw): "listen for the 'dbapi_error' event" conn = kw['conn'] cursor = kw['cursor'] # ... (event handling logic) ...
Deprecated since version 0.9: The
ConnectionEvents.dbapi_error()
event is deprecated and will be removed in a future release. Please refer to theConnectionEvents.handle_error()
event.This event is called with the DBAPI exception instance received from the DBAPI itself, before SQLAlchemy wraps the exception with it’s own exception wrappers, and before any other operations are performed on the DBAPI cursor; the existing transaction remains in effect as well as any state on the cursor.
The use case here is to inject low-level exception handling into an
Engine
, typically for logging and debugging purposes.Warning
Code should not modify any state or throw any exceptions here as this will interfere with SQLAlchemy’s cleanup and error handling routines. For exception modification, please refer to the new
ConnectionEvents.handle_error()
event.Subsequent to this hook, SQLAlchemy may attempt any number of operations on the connection/cursor, including closing the cursor, rolling back of the transaction in the case of connectionless execution, and disposing of the entire connection pool if a “disconnect” was detected. The exception is then wrapped in a SQLAlchemy DBAPI exception wrapper and re-thrown.
- Parameters:
conn¶ –
Connection
objectcursor¶ – DBAPI cursor object
statement¶ – string SQL statement, as passed to the DBAPI
parameters¶ – Dictionary, tuple, or list of parameters being passed to the
execute()
orexecutemany()
method of the DBAPIcursor
. In some cases may beNone
.context¶ –
ExecutionContext
object in use. May beNone
.exception¶ – The unwrapped exception emitted directly from the DBAPI. The class here is specific to the DBAPI module in use.
-
method
sqlalchemy.events.ConnectionEvents.
engine_connect(conn, branch)¶ Intercept the creation of a new
Connection
.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'engine_connect') def receive_engine_connect(conn, branch): "listen for the 'engine_connect' event" # ... (event handling logic) ...
This event is called typically as the direct result of calling the
Engine.connect()
method.It differs from the
PoolEvents.connect()
method, which refers to the actual connection to a database at the DBAPI level; a DBAPI connection may be pooled and reused for many operations. In contrast, this event refers only to the production of a higher levelConnection
wrapper around such a DBAPI connection.It also differs from the
PoolEvents.checkout()
event in that it is specific to theConnection
object, not the DBAPI connection thatPoolEvents.checkout()
deals with, although this DBAPI connection is available here via theConnection.connection
attribute. But note there can in fact be multiplePoolEvents.checkout()
events within the lifespan of a singleConnection
object, if thatConnection
is invalidated and re-established. There can also be multipleConnection
objects generated for the same already-checked-out DBAPI connection, in the case that a “branch” of aConnection
is produced.- Parameters:
conn¶ –
Connection
object.branch¶ – if True, this is a “branch” of an existing
Connection
. A branch is generated within the course of a statement execution to invoke supplemental statements, most typically to pre-execute a SELECT of a default value for the purposes of an INSERT statement.
New in version 0.9.0.
See also
Disconnect Handling - Pessimistic - illustrates how to use
ConnectionEvents.engine_connect()
to transparently ensure pooled connections are connected to the database.PoolEvents.checkout()
the lower-level pool checkout event for an individual DBAPI connectionConnectionEvents.set_connection_execution_options()
- a copy of aConnection
is also made when theConnection.execution_options()
method is called.
-
method
sqlalchemy.events.ConnectionEvents.
engine_disposed(engine)¶ Intercept when the
Engine.dispose()
method is called.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'engine_disposed') def receive_engine_disposed(engine): "listen for the 'engine_disposed' event" # ... (event handling logic) ...
The
Engine.dispose()
method instructs the engine to “dispose” of it’s connection pool (e.g.Pool
), and replaces it with a new one. Disposing of the old pool has the effect that existing checked-in connections are closed. The new pool does not establish any new connections until it is first used.This event can be used to indicate that resources related to the
Engine
should also be cleaned up, keeping in mind that theEngine
can still be used for new requests in which case it re-acquires connection resources.New in version 1.0.5.
-
method
sqlalchemy.events.ConnectionEvents.
handle_error(exception_context)¶ Intercept all exceptions processed by the
Connection
.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'handle_error') def receive_handle_error(exception_context): "listen for the 'handle_error' event" # ... (event handling logic) ...
This includes all exceptions emitted by the DBAPI as well as within SQLAlchemy’s statement invocation process, including encoding errors and other statement validation errors. Other areas in which the event is invoked include transaction begin and end, result row fetching, cursor creation.
Note that
handle_error()
may support new kinds of exceptions and new calling scenarios at any time. Code which uses this event must expect new calling patterns to be present in minor releases.To support the wide variety of members that correspond to an exception, as well as to allow extensibility of the event without backwards incompatibility, the sole argument received is an instance of
ExceptionContext
. This object contains data members representing detail about the exception.Use cases supported by this hook include:
read-only, low-level exception handling for logging and debugging purposes
exception re-writing
Establishing or disabling whether a connection or the owning connection pool is invalidated or expired in response to a specific exception. [1].
The hook is called while the cursor from the failed operation (if any) is still open and accessible. Special cleanup operations can be called on this cursor; SQLAlchemy will attempt to close this cursor subsequent to this hook being invoked. If the connection is in “autocommit” mode, the transaction also remains open within the scope of this hook; the rollback of the per-statement transaction also occurs after the hook is called.
Note
A handler function has two options for replacing the SQLAlchemy-constructed exception into one that is user defined. It can either raise this new exception directly, in which case all further event listeners are bypassed and the exception will be raised, after appropriate cleanup as taken place:
@event.listens_for(Engine, "handle_error") def handle_exception(context): if isinstance(context.original_exception, psycopg2.OperationalError) and \ "failed" in str(context.original_exception): raise MySpecialException("failed operation")
Warning
Because the
ConnectionEvents.handle_error()
event specifically provides for exceptions to be re-thrown as the ultimate exception raised by the failed statement, stack traces will be misleading if the user-defined event handler itself fails and throws an unexpected exception; the stack trace may not illustrate the actual code line that failed! It is advised to code carefully here and use logging and/or inline debugging if unexpected exceptions are occurring.Alternatively, a “chained” style of event handling can be used, by configuring the handler with the
retval=True
modifier and returning the new exception instance from the function. In this case, event handling will continue onto the next handler. The “chained” exception is available usingExceptionContext.chained_exception
:@event.listens_for(Engine, "handle_error", retval=True) def handle_exception(context): if context.chained_exception is not None and \ "special" in context.chained_exception.message: return MySpecialException("failed", cause=context.chained_exception)
Handlers that return
None
may be used within the chain; when a handler returnsNone
, the previous exception instance, if any, is maintained as the current exception that is passed onto the next handler.When a custom exception is raised or returned, SQLAlchemy raises this new exception as-is, it is not wrapped by any SQLAlchemy object. If the exception is not a subclass of
sqlalchemy.exc.StatementError
, certain features may not be available; currently this includes the ORM’s feature of adding a detail hint about “autoflush” to exceptions raised within the autoflush process.- Parameters:
context¶ – an
ExceptionContext
object. See this class for details on all available members.
New in version 0.9.7: Added the
ConnectionEvents.handle_error()
hook.Changed in version 1.1: The
handle_error()
event will now receive all exceptions that inherit fromBaseException
, includingSystemExit
andKeyboardInterrupt
. The setting forExceptionContext.is_disconnect
isTrue
in this case and the default forExceptionContext.invalidate_pool_on_disconnect
isFalse
.Changed in version 1.0.0: The
handle_error()
event is now invoked when anEngine
fails during the initial call toEngine.connect()
, as well as when aConnection
object encounters an error during a reconnect operation.Changed in version 1.0.0: The
handle_error()
event is not fired off when a dialect makes use of theskip_user_error_events
execution option. This is used by dialects which intend to catch SQLAlchemy-specific exceptions within specific operations, such as when the MySQL dialect detects a table not present within thehas_table()
dialect method. Prior to 1.0.0, code which implementshandle_error()
needs to ensure that exceptions thrown in these scenarios are re-raised without modification.
-
method
sqlalchemy.events.ConnectionEvents.
prepare_twophase(conn, xid)¶ Intercept prepare_twophase() events.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'prepare_twophase') def receive_prepare_twophase(conn, xid): "listen for the 'prepare_twophase' event" # ... (event handling logic) ...
- Parameters:
conn¶ –
Connection
objectxid¶ – two-phase XID identifier
-
method
sqlalchemy.events.ConnectionEvents.
release_savepoint(conn, name, context)¶ Intercept release_savepoint() events.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'release_savepoint') def receive_release_savepoint(conn, name, context): "listen for the 'release_savepoint' event" # ... (event handling logic) ...
- Parameters:
conn¶ –
Connection
objectname¶ – specified name used for the savepoint.
context¶ –
ExecutionContext
in use. May beNone
.
-
method
sqlalchemy.events.ConnectionEvents.
rollback(conn)¶ Intercept rollback() events, as initiated by a
Transaction
.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'rollback') def receive_rollback(conn): "listen for the 'rollback' event" # ... (event handling logic) ...
Note that the
Pool
also “auto-rolls back” a DBAPI connection upon checkin, if thereset_on_return
flag is set to its default value of'rollback'
. To intercept this rollback, use thePoolEvents.reset()
hook.- Parameters:
conn¶ –
Connection
object
See also
-
method
sqlalchemy.events.ConnectionEvents.
rollback_savepoint(conn, name, context)¶ Intercept rollback_savepoint() events.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'rollback_savepoint') def receive_rollback_savepoint(conn, name, context): "listen for the 'rollback_savepoint' event" # ... (event handling logic) ...
- Parameters:
conn¶ –
Connection
objectname¶ – specified name used for the savepoint.
context¶ –
ExecutionContext
in use. May beNone
.
-
method
sqlalchemy.events.ConnectionEvents.
rollback_twophase(conn, xid, is_prepared)¶ Intercept rollback_twophase() events.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'rollback_twophase') def receive_rollback_twophase(conn, xid, is_prepared): "listen for the 'rollback_twophase' event" # ... (event handling logic) ...
- Parameters:
conn¶ –
Connection
objectxid¶ – two-phase XID identifier
is_prepared¶ – boolean, indicates if
TwoPhaseTransaction.prepare()
was called.
-
method
sqlalchemy.events.ConnectionEvents.
savepoint(conn, name)¶ Intercept savepoint() events.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'savepoint') def receive_savepoint(conn, name): "listen for the 'savepoint' event" # ... (event handling logic) ...
- Parameters:
conn¶ –
Connection
objectname¶ – specified name used for the savepoint.
-
method
sqlalchemy.events.ConnectionEvents.
set_connection_execution_options(conn, opts)¶ Intercept when the
Connection.execution_options()
method is called.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'set_connection_execution_options') def receive_set_connection_execution_options(conn, opts): "listen for the 'set_connection_execution_options' event" # ... (event handling logic) ...
This method is called after the new
Connection
has been produced, with the newly updated execution options collection, but before theDialect
has acted upon any of those new options.Note that this method is not called when a new
Connection
is produced which is inheriting execution options from its parentEngine
; to intercept this condition, use theConnectionEvents.engine_connect()
event.- Parameters:
conn¶ – The newly copied
Connection
objectopts¶ – dictionary of options that were passed to the
Connection.execution_options()
method.
New in version 0.9.0.
See also
ConnectionEvents.set_engine_execution_options()
- event which is called whenEngine.execution_options()
is called.
-
method
sqlalchemy.events.ConnectionEvents.
set_engine_execution_options(engine, opts)¶ Intercept when the
Engine.execution_options()
method is called.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'set_engine_execution_options') def receive_set_engine_execution_options(engine, opts): "listen for the 'set_engine_execution_options' event" # ... (event handling logic) ...
The
Engine.execution_options()
method produces a shallow copy of theEngine
which stores the new options. That newEngine
is passed here. A particular application of this method is to add aConnectionEvents.engine_connect()
event handler to the givenEngine
which will perform some per-Connection
task specific to these execution options.- Parameters:
opts¶ – dictionary of options that were passed to the
Connection.execution_options()
method.
New in version 0.9.0.
See also
ConnectionEvents.set_connection_execution_options()
- event which is called whenConnection.execution_options()
is called.
- class sqlalchemy.events.DialectEvents¶
event interface for execution-replacement functions.
These events allow direct instrumentation and replacement of key dialect functions which interact with the DBAPI.
Note
DialectEvents
hooks should be considered semi-public and experimental. These hooks are not for general use and are only for those situations where intricate re-statement of DBAPI mechanics must be injected onto an existing dialect. For general-use statement-interception events, please use theConnectionEvents
interface.See also
ConnectionEvents.before_cursor_execute()
ConnectionEvents.before_execute()
New in version 0.9.4.
Class signature
class
sqlalchemy.events.DialectEvents
(sqlalchemy.event.Events
)-
method
sqlalchemy.events.DialectEvents.
do_connect(dialect, conn_rec, cargs, cparams)¶ Receive connection arguments before a connection is made.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'do_connect') def receive_do_connect(dialect, conn_rec, cargs, cparams): "listen for the 'do_connect' event" # ... (event handling logic) ... # named argument style (new in 0.9) @event.listens_for(SomeEngine, 'do_connect', named=True) def receive_do_connect(**kw): "listen for the 'do_connect' event" dialect = kw['dialect'] conn_rec = kw['conn_rec'] # ... (event handling logic) ...
Return a DBAPI connection to halt further events from invoking; the returned connection will be used.
Alternatively, the event can manipulate the cargs and/or cparams collections; cargs will always be a Python list that can be mutated in-place and cparams a Python dictionary. Return None to allow control to pass to the next event handler and ultimately to allow the dialect to connect normally, given the updated arguments.
New in version 1.0.3.
-
method
sqlalchemy.events.DialectEvents.
do_execute(cursor, statement, parameters, context)¶ Receive a cursor to have execute() called.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'do_execute') def receive_do_execute(cursor, statement, parameters, context): "listen for the 'do_execute' event" # ... (event handling logic) ... # named argument style (new in 0.9) @event.listens_for(SomeEngine, 'do_execute', named=True) def receive_do_execute(**kw): "listen for the 'do_execute' event" cursor = kw['cursor'] statement = kw['statement'] # ... (event handling logic) ...
Return the value True to halt further events from invoking, and to indicate that the cursor execution has already taken place within the event handler.
-
method
sqlalchemy.events.DialectEvents.
do_execute_no_params(cursor, statement, context)¶ Receive a cursor to have execute() with no parameters called.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'do_execute_no_params') def receive_do_execute_no_params(cursor, statement, context): "listen for the 'do_execute_no_params' event" # ... (event handling logic) ...
Return the value True to halt further events from invoking, and to indicate that the cursor execution has already taken place within the event handler.
-
method
sqlalchemy.events.DialectEvents.
do_executemany(cursor, statement, parameters, context)¶ Receive a cursor to have executemany() called.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'do_executemany') def receive_do_executemany(cursor, statement, parameters, context): "listen for the 'do_executemany' event" # ... (event handling logic) ... # named argument style (new in 0.9) @event.listens_for(SomeEngine, 'do_executemany', named=True) def receive_do_executemany(**kw): "listen for the 'do_executemany' event" cursor = kw['cursor'] statement = kw['statement'] # ... (event handling logic) ...
Return the value True to halt further events from invoking, and to indicate that the cursor execution has already taken place within the event handler.
-
method
sqlalchemy.events.DialectEvents.
do_setinputsizes(inputsizes, cursor, statement, parameters, context)¶ Receive the setinputsizes dictionary for possible modification.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeEngine, 'do_setinputsizes') def receive_do_setinputsizes(inputsizes, cursor, statement, parameters, context): "listen for the 'do_setinputsizes' event" # ... (event handling logic) ... # named argument style (new in 0.9) @event.listens_for(SomeEngine, 'do_setinputsizes', named=True) def receive_do_setinputsizes(**kw): "listen for the 'do_setinputsizes' event" inputsizes = kw['inputsizes'] cursor = kw['cursor'] # ... (event handling logic) ...
This event is emitted in the case where the dialect makes use of the DBAPI
cursor.setinputsizes()
method which passes information about parameter binding for a particular statement. The giveninputsizes
dictionary will containBindParameter
objects as keys, linked to DBAPI-specific type objects as values; for parameters that are not bound, they are added to the dictionary withNone
as the value, which means the parameter will not be included in the ultimate setinputsizes call. The event may be used to inspect and/or log the datatypes that are being bound, as well as to modify the dictionary in place. Parameters can be added, modified, or removed from this dictionary. Callers will typically want to inspect theBindParameter.type
attribute of the given bind objects in order to make decisions about the DBAPI object.After the event, the
inputsizes
dictionary is converted into an appropriate datastructure to be passed tocursor.setinputsizes
; either a list for a positional bound parameter execution style, or a dictionary of string parameter keys to DBAPI type objects for a named bound parameter execution style.Most dialects do not use this method at all; the only built-in dialect which uses this hook is the cx_Oracle dialect. The hook here is made available so as to allow customization of how datatypes are set up with the cx_Oracle DBAPI.
New in version 1.2.9.
-
method
Schema Events¶
Object Name | Description |
---|---|
Define event listeners for schema objects,
that is, |
|
Base class for elements that are the targets of |
- class sqlalchemy.events.DDLEvents¶
Define event listeners for schema objects, that is,
SchemaItem
and otherSchemaEventTarget
subclasses, includingMetaData
,Table
,Column
.MetaData
andTable
support events specifically regarding when CREATE and DROP DDL is emitted to the database.Attachment events are also provided to customize behavior whenever a child schema element is associated with a parent, such as, when a
Column
is associated with itsTable
, when aForeignKeyConstraint
is associated with aTable
, etc.Example using the
after_create
event:from sqlalchemy import event from sqlalchemy import Table, Column, Metadata, Integer m = MetaData() some_table = Table('some_table', m, Column('data', Integer)) def after_create(target, connection, **kw): connection.execute("ALTER TABLE %s SET name=foo_%s" % (target.name, target.name)) event.listen(some_table, "after_create", after_create)
DDL events integrate closely with the
DDL
class and theDDLElement
hierarchy of DDL clause constructs, which are themselves appropriate as listener callables:from sqlalchemy import DDL event.listen( some_table, "after_create", DDL("ALTER TABLE %(table)s SET name=foo_%(table)s") )
The methods here define the name of an event as well as the names of members that are passed to listener functions.
For all
DDLEvent
events, thepropagate=True
keyword argument will ensure that a given event handler is propagated to copies of the object, which are made when using theTable.tometadata()
method:from sqlalchemy import DDL event.listen( some_table, "after_create", DDL("ALTER TABLE %(table)s SET name=foo_%(table)s"), propagate=True ) new_table = some_table.tometadata(new_metadata)
The above
DDL
object will also be associated with theTable
object represented bynew_table
.Members
after_create(), after_drop(), after_parent_attach(), before_create(), before_drop(), before_parent_attach(), column_reflect()
Class signature
class
sqlalchemy.events.DDLEvents
(sqlalchemy.event.Events
)-
method
sqlalchemy.events.DDLEvents.
after_create(target, connection, **kw)¶ Called after CREATE statements are emitted.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeSchemaClassOrObject, 'after_create') def receive_after_create(target, connection, **kw): "listen for the 'after_create' event" # ... (event handling logic) ...
- Parameters:
target¶ – the
MetaData
orTable
object which is the target of the event.connection¶ – the
Connection
where the CREATE statement or statements have been emitted.**kw¶ – additional keyword arguments relevant to the event. The contents of this dictionary may vary across releases, and include the list of tables being generated for a metadata-level event, the checkfirst flag, and other elements used by internal events.
listen()
also accepts thepropagate=True
modifier for this event; when True, the listener function will be established for any copies made of the target object, i.e. those copies that are generated whenTable.tometadata()
is used.
-
method
sqlalchemy.events.DDLEvents.
after_drop(target, connection, **kw)¶ Called after DROP statements are emitted.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeSchemaClassOrObject, 'after_drop') def receive_after_drop(target, connection, **kw): "listen for the 'after_drop' event" # ... (event handling logic) ...
- Parameters:
target¶ – the
MetaData
orTable
object which is the target of the event.connection¶ – the
Connection
where the DROP statement or statements have been emitted.**kw¶ – additional keyword arguments relevant to the event. The contents of this dictionary may vary across releases, and include the list of tables being generated for a metadata-level event, the checkfirst flag, and other elements used by internal events.
listen()
also accepts thepropagate=True
modifier for this event; when True, the listener function will be established for any copies made of the target object, i.e. those copies that are generated whenTable.tometadata()
is used.
-
method
sqlalchemy.events.DDLEvents.
after_parent_attach(target, parent)¶ Called after a
SchemaItem
is associated with a parentSchemaItem
.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeSchemaClassOrObject, 'after_parent_attach') def receive_after_parent_attach(target, parent): "listen for the 'after_parent_attach' event" # ... (event handling logic) ...
listen()
also accepts thepropagate=True
modifier for this event; when True, the listener function will be established for any copies made of the target object, i.e. those copies that are generated whenTable.tometadata()
is used.
-
method
sqlalchemy.events.DDLEvents.
before_create(target, connection, **kw)¶ Called before CREATE statements are emitted.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeSchemaClassOrObject, 'before_create') def receive_before_create(target, connection, **kw): "listen for the 'before_create' event" # ... (event handling logic) ...
- Parameters:
target¶ – the
MetaData
orTable
object which is the target of the event.connection¶ – the
Connection
where the CREATE statement or statements will be emitted.**kw¶ – additional keyword arguments relevant to the event. The contents of this dictionary may vary across releases, and include the list of tables being generated for a metadata-level event, the checkfirst flag, and other elements used by internal events.
listen()
also accepts thepropagate=True
modifier for this event; when True, the listener function will be established for any copies made of the target object, i.e. those copies that are generated whenTable.tometadata()
is used.
-
method
sqlalchemy.events.DDLEvents.
before_drop(target, connection, **kw)¶ Called before DROP statements are emitted.
Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeSchemaClassOrObject, 'before_drop') def receive_before_drop(target, connection, **kw): "listen for the 'before_drop' event" # ... (event handling logic) ...
- Parameters:
target¶ – the
MetaData
orTable
object which is the target of the event.connection¶ – the
Connection
where the DROP statement or statements will be emitted.**kw¶ – additional keyword arguments relevant to the event. The contents of this dictionary may vary across releases, and include the list of tables being generated for a metadata-level event, the checkfirst flag, and other elements used by internal events.
listen()
also accepts thepropagate=True
modifier for this event; when True, the listener function will be established for any copies made of the target object, i.e. those copies that are generated whenTable.tometadata()
is used.
-
method
sqlalchemy.events.DDLEvents.
before_parent_attach(target, parent)¶ Called before a
SchemaItem
is associated with a parentSchemaItem
.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeSchemaClassOrObject, 'before_parent_attach') def receive_before_parent_attach(target, parent): "listen for the 'before_parent_attach' event" # ... (event handling logic) ...
listen()
also accepts thepropagate=True
modifier for this event; when True, the listener function will be established for any copies made of the target object, i.e. those copies that are generated whenTable.tometadata()
is used.
-
method
sqlalchemy.events.DDLEvents.
column_reflect(inspector, table, column_info)¶ Called for each unit of ‘column info’ retrieved when a
Table
is being reflected.Example argument forms:
from sqlalchemy import event # standard decorator style @event.listens_for(SomeSchemaClassOrObject, 'column_reflect') def receive_column_reflect(inspector, table, column_info): "listen for the 'column_reflect' event" # ... (event handling logic) ...
Currently, this event may only be applied to the
Table
class directly:from sqlalchemy import Table @event.listens_for(Table, 'column_reflect') def receive_column_reflect(inspector, table, column_info): # receives for all Table objects that are reflected
Or applied using the
Table.listeners
parameter:t1 = Table( "my_table", autoload_with=some_engine, listeners=[ ('column_reflect', receive_column_reflect) ] )
A future release will allow it to be associated with a specific
MetaData
object as well.The dictionary of column information as returned by the dialect is passed, and can be modified. The dictionary is that returned in each element of the list returned by
Inspector.get_columns()
:name
- the column’s name, is applied to theColumn.name
parametertype
- the type of this column, which should be an instance ofTypeEngine
, is applied to theColumn.type
parameternullable
- boolean flag if the column is NULL or NOT NULL, is applied to theColumn.nullable
parameterdefault
- the column’s server default value. This is normally specified as a plain string SQL expression, however the event can pass aFetchedValue
,DefaultClause
, ortext()
object as well. Is applied to theColumn.server_default
parameterChanged in version 1.1.6: The
DDLEvents.column_reflect()
event allows a non stringFetchedValue
,text()
, or derived object to be specified as the value ofdefault
in the column dictionary.
The event is called before any action is taken against this dictionary, and the contents can be modified; the following additional keys may be added to the dictionary to further modify how the
Column
is constructed:key
- the string key that will be used to access thisColumn
in the.c
collection; will be applied to theColumn.key
parameter. Is also used for ORM mapping. See the section Automating Column Naming Schemes from Reflected Tables for an example.quote
- force or un-force quoting on the column name; is applied to theColumn.quote
parameter.info
- a dictionary of arbitrary data to follow along with theColumn
, is applied to theColumn.info
parameter.
listen()
also accepts thepropagate=True
modifier for this event; when True, the listener function will be established for any copies made of the target object, i.e. those copies that are generated whenTable.to_metadata()
is used.
-
method
- class sqlalchemy.events.SchemaEventTarget¶
Base class for elements that are the targets of
DDLEvents
events.This includes
SchemaItem
as well asSchemaType
.
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