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.
A key design philosophy to the :mod:`alembic.operations` 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: