Edit File: ops.rst
.. _ops: =================== Operation Reference =================== This file provides documentation on Alembic migration directives. The directives here are used within user-defined migration files, within the ``upgrade()`` and ``downgrade()`` functions, as well as any functions further invoked by those. All directives exist as methods on a class called :class:`.Operations`. When migration scripts are run, this object is made available to the script via the ``alembic.op`` datamember, which is a *proxy* to an actual instance of :class:`.Operations`. Currently, ``alembic.op`` is a real Python module, populated with individual proxies for each method on :class:`.Operations`, so symbols can be imported safely from the ``alembic.op`` namespace. The :class:`.Operations` system is also fully extensible. See :ref:`operation_plugins` for details on this. A key design philosophy to the :ref:`alembic.operations.toplevel` methods is that to the greatest degree possible, they internally generate the appropriate SQLAlchemy metadata, typically involving :class:`~sqlalchemy.schema.Table` and :class:`~sqlalchemy.schema.Constraint` objects. This so that migration instructions can be given in terms of just the string names and/or flags involved. The exceptions to this rule include the :meth:`~.Operations.add_column` and :meth:`~.Operations.create_table` directives, which require full :class:`~sqlalchemy.schema.Column` objects, though the table metadata is still generated here. The functions here all require that a :class:`.MigrationContext` has been configured within the ``env.py`` script first, which is typically via :meth:`.EnvironmentContext.configure`. Under normal circumstances they are called from an actual migration script, which itself would be invoked by the :meth:`.EnvironmentContext.run_migrations` method. .. automodule:: alembic.operations :members: Operations, BatchOperations