Classe « QueryEvents »

Méthode sqlalchemy.orm.QueryEvents.before_compile_update

Signature de la méthode before_compile_update

def before_compile_update(self, query, update_context) 

Description

before_compile_update.__doc__

Allow modifications to the :class:`_query.Query` object within
:meth:`_query.Query.update`.

.. container:: event_signatures

     Example argument forms::

        from sqlalchemy import event


        @event.listens_for(SomeQuery, 'before_compile_update')
        def receive_before_compile_update(query, update_context):
            "listen for the 'before_compile_update' event"

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


.. deprecated:: 1.4  The :meth:`_orm.QueryEvents.before_compile_update`
   event is superseded by the much more capable
   :meth:`_orm.SessionEvents.do_orm_execute` hook.

Like the :meth:`.QueryEvents.before_compile` event, if the event
is to be used to alter the :class:`_query.Query` object, it should
be configured with ``retval=True``, and the modified
:class:`_query.Query` object returned, as in ::

    @event.listens_for(Query, "before_compile_update", retval=True)
    def no_deleted(query, update_context):
        for desc in query.column_descriptions:
            if desc['type'] is User:
                entity = desc['entity']
                query = query.filter(entity.deleted == False)

                update_context.values['timestamp'] = datetime.utcnow()
        return query

The ``.values`` dictionary of the "update context" object can also
be modified in place as illustrated above.

:param query: a :class:`_query.Query` instance; this is also
 the ``.query`` attribute of the given "update context"
 object.

:param update_context: an "update context" object which is
 the same kind of object as described in
 :paramref:`.QueryEvents.after_bulk_update.update_context`.
 The object has a ``.values`` attribute in an UPDATE context which is
 the dictionary of parameters passed to :meth:`_query.Query.update`.
 This
 dictionary can be modified to alter the VALUES clause of the
 resulting UPDATE statement.

.. versionadded:: 1.2.17

.. seealso::

    :meth:`.QueryEvents.before_compile`

    :meth:`.QueryEvents.before_compile_delete`