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Classe « MapperEvents »

Méthode sqlalchemy.orm.MapperEvents.instrument_class

Signature de la méthode instrument_class

def instrument_class(self, mapper: 'Mapper[_O]', class_: 'Type[_O]') -> 'None' 

Description

help(MapperEvents.instrument_class)

Receive a class when the mapper is first constructed,
before instrumentation is applied to the mapped class.

.. container:: event_signatures

     Example argument forms::

        from sqlalchemy import event


        @event.listens_for(SomeClass, 'instrument_class')
        def receive_instrument_class(mapper, class_):
            "listen for the 'instrument_class' event"

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


This event is the earliest phase of mapper construction.
Most attributes of the mapper are not yet initialized.   To
receive an event within initial mapper construction where basic
state is available such as the :attr:`_orm.Mapper.attrs` collection,
the :meth:`_orm.MapperEvents.after_mapper_constructed` event may
be a better choice.

This listener can either be applied to the :class:`_orm.Mapper`
class overall, or to any un-mapped class which serves as a base
for classes that will be mapped (using the ``propagate=True`` flag)::

    Base = declarative_base()


    @event.listens_for(Base, "instrument_class", propagate=True)
    def on_new_class(mapper, cls_):
        "..."

:param mapper: the :class:`_orm.Mapper` which is the target
 of this event.
:param class\_: the mapped class.

.. seealso::

    :meth:`_orm.MapperEvents.after_mapper_constructed`

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