Method execute_if

lib/sqlalchemy/sql/ddl.py:244–327

r"""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("m

(
        self,
        dialect: Optional[str] = None,
        callable_: Optional[DDLIfCallable] = None,
        state: Optional[Any] = None,
    )

    @_generative
    def execute_if(
        self,
        dialect: Optional[str] = None,
        callable_: Optional[DDLIfCallable] = None,
        state: Optional[Any] = None,
    ) -> Self:
        r"""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.