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# Copyright (C) 2005-2011 the SQLAlchemy authors and contributors <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
"""Core event interfaces."""
from sqlalchemy import event, exc, util
engine = util.importlater('sqlalchemy', 'engine')
pool = util.importlater('sqlalchemy', 'pool')
class DDLEvents(event.Events):
"""
Define event listeners for schema objects,
that is, :class:`.SchemaItem` and :class:`.SchemaEvent`
subclasses, including :class:`.MetaData`, :class:`.Table`,
:class:`.Column`.
:class:`.MetaData` and :class:`.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 :class:`.Column` is associated
with its :class:`.Table`, when a :class:`.ForeignKeyConstraint`
is associated with a :class:`.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
:class:`.DDL` class and the :class:`.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.
See also:
:ref:`event_toplevel`
:class:`.DDLElement`
:class:`.DDL`
:ref:`schema_ddl_sequences`
"""
def before_create(self, target, connection, **kw):
"""Called before CREATE statments are emitted.
:param target: the :class:`.MetaData` or :class:`.Table`
object which is the target of the event.
:param connection: the :class:`.Connection` where the
CREATE statement or statements will be emitted.
:param \**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.
"""
def after_create(self, target, connection, **kw):
"""Called after CREATE statments are emitted.
:param target: the :class:`.MetaData` or :class:`.Table`
object which is the target of the event.
:param connection: the :class:`.Connection` where the
CREATE statement or statements have been emitted.
:param \**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.
"""
def before_drop(self, target, connection, **kw):
"""Called before DROP statments are emitted.
:param target: the :class:`.MetaData` or :class:`.Table`
object which is the target of the event.
:param connection: the :class:`.Connection` where the
DROP statement or statements will be emitted.
:param \**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.
"""
def after_drop(self, target, connection, **kw):
"""Called after DROP statments are emitted.
:param target: the :class:`.MetaData` or :class:`.Table`
object which is the target of the event.
:param connection: the :class:`.Connection` where the
DROP statement or statements have been emitted.
:param \**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.
"""
def before_parent_attach(self, target, parent):
"""Called before a :class:`.SchemaItem` is associated with
a parent :class:`.SchemaItem`.
:param target: the target object
:param parent: the parent to which the target is being attached.
:func:`.event.listen` also accepts a modifier for this event:
:param propagate=False: When True, the listener function will
be established for any copies made of the target object,
i.e. those copies that are generated when
:meth:`.Table.tometadata` is used.
"""
def after_parent_attach(self, target, parent):
"""Called after a :class:`.SchemaItem` is associated with
a parent :class:`.SchemaItem`.
:param target: the target object
:param parent: the parent to which the target is being attached.
:func:`.event.listen` also accepts a modifier for this event:
:param propagate=False: When True, the listener function will
be established for any copies made of the target object,
i.e. those copies that are generated when
:meth:`.Table.tometadata` is used.
"""
def column_reflect(self, table, column_info):
"""Called for each unit of 'column info' retrieved when
a :class:`.Table` is being reflected.
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 :meth:`.reflection.Inspector.get_columns`.
The event is called before any action is taken against
this dictionary, and the contents can be modified.
The :class:`.Column` specific arguments ``info``, ``key``,
and ``quote`` can also be added to the dictionary and
will be passed to the constructor of :class:`.Column`.
Note that this event is only meaningful if either
associated with the :class:`.Table` class across the
board, e.g.::
from sqlalchemy.schema import Table
from sqlalchemy import event
def listen_for_reflect(table, column_info):
"receive a column_reflect event"
# ...
event.listen(
Table,
'column_reflect',
listen_for_reflect)
...or with a specific :class:`.Table` instance using
the ``listeners`` argument::
def listen_for_reflect(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 :class:`.Table`.
"""
class SchemaEventTarget(object):
"""Base class for elements that are the targets of :class:`.DDLEvents` events.
This includes :class:`.SchemaItem` as well as :class:`.SchemaType`.
"""
dispatch = event.dispatcher(DDLEvents)
def _set_parent(self, parent):
"""Associate with this SchemaEvent's parent object."""
raise NotImplementedError()
def _set_parent_with_dispatch(self, parent):
self.dispatch.before_parent_attach(self, parent)
self._set_parent(parent)
self.dispatch.after_parent_attach(self, parent)
class PoolEvents(event.Events):
"""Available events for :class:`.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 :class:`.Pool` class and :class:`.Pool` instances,
:class:`.PoolEvents` also accepts :class:`.Engine` objects and
the :class:`.Engine` class as targets, which will be resolved
to the ``.pool`` attribute of the given engine or the :class:`.Pool`
class::
engine = create_engine("postgresql://scott:tiger@localhost/test")
# will associate with engine.pool
event.listen(engine, 'checkout', my_on_checkout)
"""
@classmethod
def _accept_with(cls, target):
if isinstance(target, type):
if issubclass(target, engine.Engine):
return pool.Pool
elif issubclass(target, pool.Pool):
return target
elif isinstance(target, engine.Engine):
return target.pool
else:
return target
def connect(self, dbapi_connection, connection_record):
"""Called once for each new DB-API connection or Pool's ``creator()``.
:param dbapi_con:
A newly connected raw DB-API connection (not a SQLAlchemy
``Connection`` wrapper).
:param con_record:
The ``_ConnectionRecord`` that persistently manages the connection
"""
def first_connect(self, dbapi_connection, connection_record):
"""Called exactly once for the first DB-API connection.
:param dbapi_con:
A newly connected raw DB-API connection (not a SQLAlchemy
``Connection`` wrapper).
:param con_record:
The ``_ConnectionRecord`` that persistently manages the connection
"""
def checkout(self, dbapi_connection, connection_record, connection_proxy):
"""Called when a connection is retrieved from the Pool.
:param dbapi_con:
A raw DB-API connection
:param con_record:
The ``_ConnectionRecord`` that persistently manages the connection
:param con_proxy:
The ``_ConnectionFairy`` which manages the connection for the span of
the current checkout.
If you raise a :class:`~sqlalchemy.exc.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.
"""
def checkin(self, dbapi_connection, connection_record):
"""Called when a connection returns to the pool.
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.)
:param dbapi_con:
A raw DB-API connection
:param con_record:
The ``_ConnectionRecord`` that persistently manages the connection
"""
class ConnectionEvents(event.Events):
"""Available events for :class:`.Connection`.
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, create_engine
def before_execute(conn, clauseelement, multiparams, params):
log.info("Received statement: %s" % clauseelement)
engine = create_engine('postgresql://scott:tiger@localhost/test')
event.listen(engine, "before_execute", before_execute)
Some events allow modifiers to the listen() function.
:param retval=False: Applies to the :meth:`.before_execute` and
:meth:`.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.
"""
@classmethod
def _listen(cls, target, identifier, fn, retval=False):
target._has_events = True
if not retval:
if identifier == 'before_execute':
orig_fn = fn
def wrap(conn, clauseelement, multiparams, params):
orig_fn(conn, clauseelement, multiparams, params)
return clauseelement, multiparams, params
fn = wrap
elif identifier == 'before_cursor_execute':
orig_fn = fn
def wrap(conn, cursor, statement,
parameters, context, executemany):
orig_fn(conn, cursor, statement,
parameters, context, executemany)
return statement, parameters
fn = wrap
elif retval and identifier not in ('before_execute', 'before_cursor_execute'):
raise exc.ArgumentError(
"Only the 'before_execute' and "
"'before_cursor_execute' engine "
"event listeners accept the 'retval=True' "
"argument.")
event.Events._listen(target, identifier, fn)
def before_execute(self, conn, clauseelement, multiparams, params):
"""Intercept high level execute() events."""
def after_execute(self, conn, clauseelement, multiparams, params, result):
"""Intercept high level execute() events."""
def before_cursor_execute(self, conn, cursor, statement,
parameters, context, executemany):
"""Intercept low-level cursor execute() events."""
def after_cursor_execute(self, conn, cursor, statement,
parameters, context, executemany):
"""Intercept low-level cursor execute() events."""
def begin(self, conn):
"""Intercept begin() events."""
def rollback(self, conn):
"""Intercept rollback() events."""
def commit(self, conn):
"""Intercept commit() events."""
def savepoint(self, conn, name=None):
"""Intercept savepoint() events."""
def rollback_savepoint(self, conn, name, context):
"""Intercept rollback_savepoint() events."""
def release_savepoint(self, conn, name, context):
"""Intercept release_savepoint() events."""
def begin_twophase(self, conn, xid):
"""Intercept begin_twophase() events."""
def prepare_twophase(self, conn, xid):
"""Intercept prepare_twophase() events."""
def rollback_twophase(self, conn, xid, is_prepared):
"""Intercept rollback_twophase() events."""
def commit_twophase(self, conn, xid, is_prepared):
"""Intercept commit_twophase() events."""
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