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Module « sqlalchemy.orm »

Classe « MapperEvents »

Informations générales

Héritage

builtins.object
    Generic
        _HasEventsDispatch
            Events
                MapperEvents

Définition

class MapperEvents(Events):

help(MapperEvents)

Define events specific to mappings.

e.g.::

    from sqlalchemy import event


    def my_before_insert_listener(mapper, connection, target):
        # execute a stored procedure upon INSERT,
        # apply the value to the row to be inserted
        target.calculated_value = connection.execute(
            text("select my_special_function(%d)" % target.special_number)
        ).scalar()


    # associate the listener function with SomeClass,
    # to execute during the "before_insert" hook
    event.listen(SomeClass, "before_insert", my_before_insert_listener)

Available targets include:

* mapped classes
* unmapped superclasses of mapped or to-be-mapped classes
  (using the ``propagate=True`` flag)
* :class:`_orm.Mapper` objects
* the :class:`_orm.Mapper` class itself indicates listening for all
  mappers.

Mapper events provide hooks into critical sections of the
mapper, including those related to object instrumentation,
object loading, and object persistence. In particular, the
persistence methods :meth:`~.MapperEvents.before_insert`,
and :meth:`~.MapperEvents.before_update` are popular
places to augment the state being persisted - however, these
methods operate with several significant restrictions. The
user is encouraged to evaluate the
:meth:`.SessionEvents.before_flush` and
:meth:`.SessionEvents.after_flush` methods as more
flexible and user-friendly hooks in which to apply
additional database state during a flush.

When using :class:`.MapperEvents`, several modifiers are
available to the :func:`.event.listen` function.

:param propagate=False: When True, the event listener should
   be applied to all inheriting mappers and/or the mappers of
   inheriting classes, as well as any
   mapper which is the target of this listener.
:param raw=False: When True, the "target" argument passed
   to applicable event listener functions will be the
   instance's :class:`.InstanceState` management
   object, rather than the mapped instance itself.
:param retval=False: when True, the user-defined event function
   must have a return value, the purpose of which is either to
   control subsequent event propagation, or to otherwise alter
   the operation in progress by the mapper.   Possible return
   values are:

   * ``sqlalchemy.orm.interfaces.EXT_CONTINUE`` - continue event
     processing normally.
   * ``sqlalchemy.orm.interfaces.EXT_STOP`` - cancel all subsequent
     event handlers in the chain.
   * other values - the return value specified by specific listeners.

Constructeur(s)

Signature du constructeur	Description
__init__(self, /, *args, **kwargs)	Initialize self. See help(type(self)) for accurate signature. [extrait de __init__.__doc__]

Liste des opérateurs

Opérateurs hérités de la classe object

__eq__, __ge__, __gt__, __le__, __lt__, __ne__

Méthodes héritées de la classe Events

__subclasshook__

Méthodes héritées de la classe _HasEventsDispatch

__init_subclass__

Méthodes héritées de la classe object

__delattr__, __dir__, __format__, __getattribute__, __getstate__, __hash__, __reduce__, __reduce_ex__, __repr__, __setattr__, __sizeof__, __str__

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