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