Classe « MapperEvents »

Méthode sqlalchemy.orm.MapperEvents.before_delete

Signature de la méthode before_delete

def before_delete(self, mapper, connection, target) 

Description

before_delete.__doc__

Receive an object instance before a DELETE statement
is emitted corresponding to that instance.

.. container:: event_signatures

     Example argument forms::

        from sqlalchemy import event


        @event.listens_for(SomeClass, 'before_delete')
        def receive_before_delete(mapper, connection, target):
            "listen for the 'before_delete' event"

            # ... (event handling logic) ...


This event is used to emit additional SQL statements on
the given connection as well as to perform application
specific bookkeeping related to a deletion event.

The event is often called for a batch of objects of the
same class before their DELETE statements are emitted at
once in a later step.

.. warning::

    Mapper-level flush events only allow **very limited operations**,
    on attributes local to the row being operated upon only,
    as well as allowing any SQL to be emitted on the given
    :class:`_engine.Connection`.  **Please read fully** the notes
    at :ref:`session_persistence_mapper` for guidelines on using
    these methods; generally, the :meth:`.SessionEvents.before_flush`
    method should be preferred for general on-flush changes.

:param mapper: the :class:`_orm.Mapper` which is the target
 of this event.
:param connection: the :class:`_engine.Connection` being used to
 emit DELETE statements for this instance.  This
 provides a handle into the current transaction on the
 target database specific to this instance.
:param target: the mapped instance being deleted.  If
 the event is configured with ``raw=True``, this will
 instead be the :class:`.InstanceState` state-management
 object associated with the instance.
:return: No return value is supported by this event.

.. seealso::

    :ref:`session_persistence_events`