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.
sqlalchemy.event.base.Events¶Define event listening functions for a particular target type.
sqlalchemy.events.PoolEvents¶Bases: sqlalchemy.event.base.Events
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 and
Pool instances, PoolEvents also accepts
Engine objects and the Engine class as
targets, which will be resolved to the .pool attribute of the
given engine or the Pool class:
engine = create_engine("postgresql://scott:tiger@localhost/test")
# will associate with engine.pool
event.listen(engine, 'checkout', my_on_checkout)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: |
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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: |
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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 new Connection.
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 use close_detached().
New in version 1.1.
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.
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: |
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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.
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 particular
Pool refers to a single “creator” function (which in terms
of a Engine 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: |
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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 the soft flag.
The event occurs before a final attempt to call .close() on the
connection occurs.
| Parameters: |
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New in version 0.9.2: Added support for connection invalidation listening.
See also
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 the reset_on_return
pool argument.
The PoolEvents.reset() event is usually followed by the
PoolEvents.checkin() event is called, except in those
cases where the connection is discarded immediately after reset.
| Parameters: |
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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 the soft 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.
sqlalchemy.events.ConnectionEvents¶Bases: sqlalchemy.event.base.Events
Available events for Connectable, which includes
Connection and Engine.
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 an Engine, 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() and
dbapi_error(), the statement is the exact SQL string that was
prepared for transmission to the DBAPI cursor in the connection’s
Dialect.
The before_execute() and before_cursor_execute()
events can also be established with the retval=True flag, which
allows modification of the statement and parameters to be sent
to the database. The before_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, parametersNote
ConnectionEvents can be established on any
combination of Engine, Connection, as well
as instances of each of those classes. Events across all
four scopes will fire off for a given instance of
Connection. However, for performance reasons, the
Connection object determines at instantiation time
whether or not its parent Engine has event listeners
established. Event listeners added to the Engine
class or to an instance of Engine after the instantiation
of a dependent Connection instance will usually
not be available on that Connection instance. The newly
added listeners will instead take effect for Connection
instances created subsequent to those event listeners being
established on the parent Engine class or instance.
| Parameters: | retval=False¶ – Applies to the before_execute() and
before_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. |
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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: |
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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: |
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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. The statement and parameters 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, parametersSee the example at ConnectionEvents.
| Parameters: |
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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. The clauseelement, multiparams, and params
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: |
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See also
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 |
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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: |
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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 the reset_on_return
flag is set to the value 'commit'. To intercept this
commit, use the PoolEvents.reset() hook.
| Parameters: | conn¶ – Connection object |
|---|
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: |
|
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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 the ConnectionEvents.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: |
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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 level
Connection wrapper around such a DBAPI connection.
It also differs from the PoolEvents.checkout() event
in that it is specific to the Connection object, not the
DBAPI connection that PoolEvents.checkout() deals with, although
this DBAPI connection is available here via the
Connection.connection attribute. But note there can in fact
be multiple PoolEvents.checkout() events within the lifespan
of a single Connection object, if that Connection
is invalidated and re-established. There can also be multiple
Connection objects generated for the same already-checked-out
DBAPI connection, in the case that a “branch” of a Connection
is produced.
| Parameters: |
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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 connection
ConnectionEvents.set_connection_execution_options() - a copy
of a Connection is also made when the
Connection.execution_options() method is called.
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 the
Engine can still be used for new requests in which case
it re-acquires connection resources.
New in version 1.0.5.
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:
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.
For the common case of detecting a “disconnect” situation which
is not currently handled by the SQLAlchemy dialect, the
ExceptionContext.is_disconnect flag can be set to True which
will cause the exception to be considered as a disconnect situation,
which typically results in the connection pool being invalidated:
@event.listens_for(Engine, "handle_error")
def handle_exception(context):
if isinstance(context.original_exception, pyodbc.Error):
for code in (
'08S01', '01002', '08003',
'08007', '08S02', '08001', 'HYT00', 'HY010'):
if code in str(context.original_exception):
context.is_disconnect = TrueA 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 using
ExceptionContext.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 returns None, 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 from BaseException,
including SystemExit and KeyboardInterrupt. The setting for
ExceptionContext.is_disconnect is True in this case and
the default for
ExceptionContext.invalidate_pool_on_disconnect is
False.
Changed in version 1.0.0: The handle_error() event is now
invoked when an Engine fails during the initial
call to Engine.connect(), as well as when a
Connection 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 the
skip_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 the has_table() dialect method.
Prior to 1.0.0, code which implements handle_error() needs
to ensure that exceptions thrown in these scenarios are re-raised
without modification.
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: |
|
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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: |
|
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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 the reset_on_return
flag is set to its default value of 'rollback'.
To intercept this
rollback, use the PoolEvents.reset() hook.
| Parameters: | conn¶ – Connection object |
|---|
See also
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: |
|
|---|
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: |
|
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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: |
|
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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 the Dialect 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 parent
Engine; to intercept this condition, use the
ConnectionEvents.engine_connect() event.
| Parameters: |
|
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New in version 0.9.0.
See also
ConnectionEvents.set_engine_execution_options() - event
which is called when Engine.execution_options() is called.
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 the Engine which stores the new options. That new
Engine is passed here. A particular application of this
method is to add a ConnectionEvents.engine_connect() event
handler to the given Engine which will perform some per-
Connection task specific to these execution options.
| Parameters: |
|
|---|
New in version 0.9.0.
See also
ConnectionEvents.set_connection_execution_options() - event
which is called when Connection.execution_options() is
called.
sqlalchemy.events.DialectEvents¶Bases: sqlalchemy.event.base.Events
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 the ConnectionEvents interface.
See also
ConnectionEvents.before_cursor_execute()
ConnectionEvents.before_execute()
New in version 0.9.4.
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.
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.
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.
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.
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 given
inputsizes dictionary will contain BindParameter objects
as keys, linked to DBAPI-specific type objects as values; for
parameters that are not bound, they are added to the dictionary with
None 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 the
BindParameter.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 to cursor.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.
sqlalchemy.events.DDLEvents¶Bases: sqlalchemy.event.base.Events
Define event listeners for schema objects,
that is, SchemaItem and other SchemaEventTarget
subclasses, including MetaData, Table,
Column.
MetaData and Table 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 its Table, when a ForeignKeyConstraint
is associated with a Table, 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 the DDLElement 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, the propagate=True keyword argument
will ensure that a given event handler is propagated to copies of the
object, which are made when using the Table.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 the
Table object represented by new_table.
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: |
|
|---|
event.listen() also accepts the propagate=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 when
Table.tometadata() is used.
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: |
|
|---|
event.listen() also accepts the propagate=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 when
Table.tometadata() is used.
after_parent_attach(target, parent)¶Called after a SchemaItem is associated with
a parent SchemaItem.
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) ...| Parameters: |
|---|
event.listen() also accepts the propagate=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 when
Table.tometadata() is used.
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: |
|
|---|
event.listen() also accepts the propagate=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 when
Table.tometadata() is used.
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: |
|
|---|
event.listen() also accepts the propagate=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 when
Table.tometadata() is used.
before_parent_attach(target, parent)¶Called before a SchemaItem is associated with
a parent SchemaItem.
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) ...| Parameters: |
|---|
event.listen() also accepts the propagate=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 when
Table.tometadata() is used.
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) ...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 reflection.Inspector.get_columns():
name- the column’s name
type- the type of this column, which should be an instance ofTypeEngine
nullable- boolean flag if the column is NULL or NOT NULL
default- the column’s server default value. This is normally specified as a plain string SQL expression, however the event can pass aFetchedValue,DefaultClause, orsql.expression.text()object as well.Changed in version 1.1.6: The
DDLEvents.column_reflect()event allows a non stringFetchedValue,sql.expression.text(), or derived object to be specified as the value ofdefaultin the column dictionary.
attrs- dict containing optional column attributes
The event is called before any action is taken against
this dictionary, and the contents can be modified.
The Column specific arguments info, key,
and quote can also be added to the dictionary and
will be passed to the constructor of Column.
Note that this event is only meaningful if either
associated with the Table class across the
board, e.g.:
from sqlalchemy.schema import Table
from sqlalchemy import event
def listen_for_reflect(inspector, table, column_info):
"receive a column_reflect event"
# ...
event.listen(
Table,
'column_reflect',
listen_for_reflect)…or with a specific Table instance using
the listeners argument:
def listen_for_reflect(inspector, table, column_info):
"receive a column_reflect event"
# ...
t = Table(
'sometable',
autoload=True,
listeners=[
('column_reflect', listen_for_reflect)
])This because the reflection process initiated by autoload=True
completes within the scope of the constructor for Table.
event.listen() also accepts the propagate=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 when
Table.tometadata() is used.
sqlalchemy.events.SchemaEventTarget¶Base class for elements that are the targets of DDLEvents
events.
This includes SchemaItem as well as SchemaType.