# sqlalchemy/events.py # Copyright (C) 2005-2013 the SQLAlchemy authors and contributors # # 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 . 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, inspector, 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(inspector, 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(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 :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 """ def reset(self, dbapi_con, con_record): """Called before the "reset" action occurs for a pooled connection. 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 :meth:`.PoolEvents.reset` event is usually followed by the the :meth:`.PoolEvents.checkin` event is called, except in those cases where the connection is discarded immediately after reset. :param dbapi_con: A raw DB-API connection :param con_record: The ``_ConnectionRecord`` that persistently manages the connection .. versionadded:: 0.8 .. seealso:: :meth:`.ConnectionEvents.rollback` :meth:`.ConnectionEvents.commit` """ class ConnectionEvents(event.Events): """Available events for :class:`.Connectable`, which includes :class:`.Connection` and :class:`.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 :class:`.Connectable` class or instance, such as an :class:`.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 :class:`.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) The :meth:`.before_execute` and :meth:`.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 :meth:`.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, parameters .. note:: :class:`.ConnectionEvents` can be established on any combination of :class:`.Engine`, :class:`.Connection`, as well as instances of each of those classes. Events across all four scopes will fire off for a given instance of :class:`.Connection`. However, for performance reasons, the :class:`.Connection` object determines at instantiation time whether or not its parent :class:`.Engine` has event listeners established. Event listeners added to the :class:`.Engine` class or to an instance of :class:`.Engine` *after* the instantiation of a dependent :class:`.Connection` instance will usually *not* be available on that :class:`.Connection` instance. The newly added listeners will instead take effect for :class:`.Connection` instances created subsequent to those event listeners being established on the parent :class:`.Engine` class or instance. :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. .. versionchanged:: 0.8 :class:`.ConnectionEvents` can now be associated with any :class:`.Connectable` including :class:`.Connection`, in addition to the existing support for :class:`.Engine`. """ @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_before_execute(conn, clauseelement, multiparams, params): orig_fn(conn, clauseelement, multiparams, params) return clauseelement, multiparams, params fn = wrap_before_execute elif identifier == 'before_cursor_execute': orig_fn = fn def wrap_before_cursor_execute(conn, cursor, statement, parameters, context, executemany): orig_fn(conn, cursor, statement, parameters, context, executemany) return statement, parameters fn = wrap_before_cursor_execute 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, receiving uncompiled SQL constructs and other objects prior to rendering into SQL. 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, conn, clauseelement, multiparams, params): # do something with clauseelement, multiparams, params return clauseelement, multiparams, params :param conn: :class:`.Connection` object :param clauseelement: SQL expression construct, :class:`.Compiled` instance, or string statement passed to :meth:`.Connection.execute`. :param multiparams: Multiple parameter sets, a list of dictionaries. :param params: Single parameter set, a single dictionary. See also: :meth:`.before_cursor_execute` """ def after_execute(self, conn, clauseelement, multiparams, params, result): """Intercept high level execute() events after execute. :param conn: :class:`.Connection` object :param clauseelement: SQL expression construct, :class:`.Compiled` instance, or string statement passed to :meth:`.Connection.execute`. :param multiparams: Multiple parameter sets, a list of dictionaries. :param params: Single parameter set, a single dictionary. :param result: :class:`.ResultProxy` generated by the execution. """ def before_cursor_execute(self, 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. 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, parameters See the example at :class:`.ConnectionEvents`. :param conn: :class:`.Connection` object :param cursor: DBAPI cursor object :param statement: string SQL statement :param parameters: Dictionary, tuple, or list of parameters being passed to the ``execute()`` or ``executemany()`` method of the DBAPI ``cursor``. In some cases may be ``None``. :param context: :class:`.ExecutionContext` object in use. May be ``None``. :param executemany: boolean, if ``True``, this is an ``executemany()`` call, if ``False``, this is an ``execute()`` call. See also: :meth:`.before_execute` :meth:`.after_cursor_execute` """ def after_cursor_execute(self, conn, cursor, statement, parameters, context, executemany): """Intercept low-level cursor execute() events after execution. :param conn: :class:`.Connection` object :param cursor: 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 :class:`.ResultProxy`. :param statement: string SQL statement :param parameters: Dictionary, tuple, or list of parameters being passed to the ``execute()`` or ``executemany()`` method of the DBAPI ``cursor``. In some cases may be ``None``. :param context: :class:`.ExecutionContext` object in use. May be ``None``. :param executemany: boolean, if ``True``, this is an ``executemany()`` call, if ``False``, this is an ``execute()`` call. """ def dbapi_error(self, conn, cursor, statement, parameters, context, exception): """Intercept a raw DBAPI error. 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 :class:`.Engine`, typically for logging and debugging purposes. In general, user code should **not** modify any state or throw any exceptions here as this will interfere with SQLAlchemy's cleanup and error handling routines. 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. :param conn: :class:`.Connection` object :param cursor: DBAPI cursor object :param statement: string SQL statement :param parameters: Dictionary, tuple, or list of parameters being passed to the ``execute()`` or ``executemany()`` method of the DBAPI ``cursor``. In some cases may be ``None``. :param context: :class:`.ExecutionContext` object in use. May be ``None``. :param exception: The **unwrapped** exception emitted directly from the DBAPI. The class here is specific to the DBAPI module in use. .. versionadded:: 0.7.7 """ def begin(self, conn): """Intercept begin() events. :param conn: :class:`.Connection` object """ def rollback(self, conn): """Intercept rollback() events, as initiated by a :class:`.Transaction`. Note that the :class:`.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 :meth:`.PoolEvents.reset` hook. :param conn: :class:`.Connection` object .. seealso:: :meth:`.PoolEvents.reset` """ def commit(self, conn): """Intercept commit() events, as initiated by a :class:`.Transaction`. Note that the :class:`.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 :meth:`.PoolEvents.reset` hook. :param conn: :class:`.Connection` object """ def savepoint(self, conn, name=None): """Intercept savepoint() events. :param conn: :class:`.Connection` object :param name: specified name used for the savepoint. """ def rollback_savepoint(self, conn, name, context): """Intercept rollback_savepoint() events. :param conn: :class:`.Connection` object :param name: specified name used for the savepoint. :param context: :class:`.ExecutionContext` in use. May be ``None``. """ def release_savepoint(self, conn, name, context): """Intercept release_savepoint() events. :param conn: :class:`.Connection` object :param name: specified name used for the savepoint. :param context: :class:`.ExecutionContext` in use. May be ``None``. """ def begin_twophase(self, conn, xid): """Intercept begin_twophase() events. :param conn: :class:`.Connection` object :param xid: two-phase XID identifier """ def prepare_twophase(self, conn, xid): """Intercept prepare_twophase() events. :param conn: :class:`.Connection` object :param xid: two-phase XID identifier """ def rollback_twophase(self, conn, xid, is_prepared): """Intercept rollback_twophase() events. :param conn: :class:`.Connection` object :param xid: two-phase XID identifier :param is_prepared: boolean, indicates if :meth:`.TwoPhaseTransaction.prepare` was called. """ def commit_twophase(self, conn, xid, is_prepared): """Intercept commit_twophase() events. :param conn: :class:`.Connection` object :param xid: two-phase XID identifier :param is_prepared: boolean, indicates if :meth:`.TwoPhaseTransaction.prepare` was called. """