Module « sqlalchemy.orm »

Classe « AttributeEvents »

Informations générales

Héritage

builtins.object
    Events
        AttributeEvents

Définition

class AttributeEvents(Events):

Description _{[extrait de AttributeEvents.__doc__]}

Define events for object attributes.

    These are typically defined on the class-bound descriptor for the
    target class.

    e.g.::

        from sqlalchemy import event

        @event.listens_for(MyClass.collection, 'append', propagate=True)
        def my_append_listener(target, value, initiator):
            print("received append event for target: %s" % target)


    Listeners have the option to return a possibly modified version of the
    value, when the :paramref:`.AttributeEvents.retval` flag is passed to
    :func:`.event.listen` or :func:`.event.listens_for`::

        def validate_phone(target, value, oldvalue, initiator):
            "Strip non-numeric characters from a phone number"

            return re.sub(r'\D', '', value)

        # setup listener on UserContact.phone attribute, instructing
        # it to use the return value
        listen(UserContact.phone, 'set', validate_phone, retval=True)

    A validation function like the above can also raise an exception
    such as :exc:`ValueError` to halt the operation.

    The :paramref:`.AttributeEvents.propagate` flag is also important when
    applying listeners to mapped classes that also have mapped subclasses,
    as when using mapper inheritance patterns::


        @event.listens_for(MySuperClass.attr, 'set', propagate=True)
        def receive_set(target, value, initiator):
            print("value set: %s" % target)

    The full list of modifiers available to the :func:`.event.listen`
    and :func:`.event.listens_for` functions are below.

    :param active_history=False: When True, indicates that the
      "set" event would like to receive the "old" value being
      replaced unconditionally, even if this requires firing off
      database loads. Note that ``active_history`` can also be
      set directly via :func:`.column_property` and
      :func:`_orm.relationship`.

    :param propagate=False: When True, the listener function will
      be established not just for the class attribute given, but
      for attributes of the same name on all current subclasses
      of that class, as well as all future subclasses of that
      class, using an additional listener that listens for
      instrumentation events.
    :param raw=False: When True, the "target" argument to the
      event will be the :class:`.InstanceState` management
      object, rather than the mapped instance itself.
    :param retval=False: when True, the user-defined event
      listening must return the "value" argument from the
      function.  This gives the listening function the opportunity
      to change the value that is ultimately used for a "set"
      or "append" event.

    

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

__init_subclass__, __subclasshook__

Méthodes héritées de la classe object

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