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Classe « ExecutableDDLElement »

Méthode sqlalchemy.ExecutableDDLElement.execute_if

Signature de la méthode execute_if

def execute_if(self, dialect: 'Optional[str]' = None, callable_: 'Optional[DDLIfCallable]' = None, state: 'Optional[Any]' = None) -> 'Self' 

Description

help(ExecutableDDLElement.execute_if)

Return a callable that will execute this
:class:`_ddl.ExecutableDDLElement` conditionally within an event
handler.

Used to provide a wrapper for event listening::

    event.listen(
        metadata,
        "before_create",
        DDL("my_ddl").execute_if(dialect="postgresql"),
    )

:param dialect: May be a string or tuple of strings.
  If a string, it will be compared to the name of the
  executing database dialect::

    DDL("something").execute_if(dialect="postgresql")

  If a tuple, specifies multiple dialect names::

    DDL("something").execute_if(dialect=("postgresql", "mysql"))

:param callable\_: A callable, which will be invoked with
  three positional arguments as well as optional keyword
  arguments:

    :ddl:
      This DDL element.

    :target:
      The :class:`_schema.Table` or :class:`_schema.MetaData`
      object which is the
      target of this event. May be None if the DDL is executed
      explicitly.

    :bind:
      The :class:`_engine.Connection` being used for DDL execution.
      May be None if this construct is being created inline within
      a table, in which case ``compiler`` will be present.

    :tables:
      Optional keyword argument - a list of Table objects which are to
      be created/ dropped within a MetaData.create_all() or drop_all()
      method call.

    :dialect: keyword argument, but always present - the
      :class:`.Dialect` involved in the operation.

    :compiler: keyword argument.  Will be ``None`` for an engine
      level DDL invocation, but will refer to a :class:`.DDLCompiler`
      if this DDL element is being created inline within a table.

    :state:
      Optional keyword argument - will be the ``state`` argument
      passed to this function.

    :checkfirst:
     Keyword argument, will be True if the 'checkfirst' flag was
     set during the call to ``create()``, ``create_all()``,
     ``drop()``, ``drop_all()``.

  If the callable returns a True value, the DDL statement will be
  executed.

:param state: any value which will be passed to the callable\_
  as the ``state`` keyword argument.

.. seealso::

    :meth:`.SchemaItem.ddl_if`

    :class:`.DDLEvents`

    :ref:`event_toplevel`

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