=============================
Database migration operations
=============================

All of these :doc:`operations </ref/migration-operations>` are available from
the ``django.contrib.postgres.operations`` module.

.. _create-postgresql-extensions:

Creating extension using migrations
===================================

You can create a PostgreSQL extension in your database using a migration file.
This example creates an hstore extension, but the same principles apply for
other extensions.

Set up the hstore extension in PostgreSQL before the first ``CreateModel``
or ``AddField`` operation that involves
:class:`~django.contrib.postgres.fields.HStoreField` by adding a migration with
the :class:`~django.contrib.postgres.operations.HStoreExtension` operation.
For example::

    from django.contrib.postgres.operations import HStoreExtension


    class Migration(migrations.Migration):
        ...

        operations = [HStoreExtension(), ...]

The operation skips adding the extension if it already exists.

For most extensions, this requires a database user with superuser privileges.
If the Django database user doesn't have the appropriate privileges, you'll
have to create the extension outside of Django migrations with a user that has
them. In that case, connect to your Django database and run the query
``CREATE EXTENSION IF NOT EXISTS hstore;``.

.. currentmodule:: django.contrib.postgres.operations

``CreateExtension``
===================

.. class:: CreateExtension(name)

    An ``Operation`` subclass which installs a PostgreSQL extension. For common
    extensions, use one of the more specific subclasses below.

    .. attribute:: name

        This is a required argument. The name of the extension to be installed.

``BloomExtension``
==================

.. class:: BloomExtension()

    Installs the ``bloom`` extension.

``BtreeGinExtension``
=====================

.. class:: BtreeGinExtension()

    Installs the ``btree_gin`` extension.

``BtreeGistExtension``
======================

.. class:: BtreeGistExtension()

    Installs the ``btree_gist`` extension.

``CITextExtension``
===================

.. class:: CITextExtension()

    Installs the ``citext`` extension.

``CryptoExtension``
===================

.. class:: CryptoExtension()

    Installs the ``pgcrypto`` extension.

``HStoreExtension``
===================

.. class:: HStoreExtension()

    Installs the ``hstore`` extension and also sets up the connection to
    interpret hstore data for possible use in subsequent migrations.

``TrigramExtension``
====================

.. class:: TrigramExtension()

    Installs the ``pg_trgm`` extension.

``UnaccentExtension``
=====================

.. class:: UnaccentExtension()

    Installs the ``unaccent`` extension.

.. _manage-postgresql-collations:

Managing collations using migrations
====================================

If you need to filter or order a column using a particular collation that your
operating system provides but PostgreSQL does not, you can manage collations in
your database using a migration file. These collations can then be used with
the ``db_collation`` parameter on :class:`~django.db.models.CharField`,
:class:`~django.db.models.TextField`, and their subclasses.

For example, to create a collation for German phone book ordering::

    from django.contrib.postgres.operations import CreateCollation


    class Migration(migrations.Migration):
        ...

        operations = [
            CreateCollation(
                "german_phonebook",
                provider="icu",
                locale="und-u-ks-level2",
            ),
            ...,
        ]

.. class:: CreateCollation(name, locale, *, provider='libc', deterministic=True)

    Creates a collation with the given ``name``, ``locale`` and ``provider``.

    Set the ``deterministic`` parameter to ``False`` to create a
    non-deterministic collation, such as for case-insensitive filtering.

.. class:: RemoveCollation(name, locale, *, provider='libc', deterministic=True)

    Removes the collations named ``name``.

    When reversed this is creating a collation with the provided ``locale``,
    ``provider``, and ``deterministic`` arguments. Therefore, ``locale`` is
    required to make this operation reversible.

Concurrent index operations
===========================

PostgreSQL supports the ``CONCURRENTLY`` option to ``CREATE INDEX`` and
``DROP INDEX`` statements to add and remove indexes without locking out writes.
This option is useful for adding or removing an index in a live production
database.

.. class:: AddIndexConcurrently(model_name, index)

    Like :class:`~django.db.migrations.operations.AddIndex`, but creates an
    index with the ``CONCURRENTLY`` option. This has a few caveats to be aware
    of when using this option, see `the PostgreSQL documentation of building
    indexes concurrently <https://www.postgresql.org/docs/current/
    sql-createindex.html#SQL-CREATEINDEX-CONCURRENTLY>`_.

.. class:: RemoveIndexConcurrently(model_name, name)

    Like :class:`~django.db.migrations.operations.RemoveIndex`, but removes the
    index with the ``CONCURRENTLY`` option. This has a few caveats to be aware
    of when using this option, see `the PostgreSQL documentation
    <https://www.postgresql.org/docs/current/sql-dropindex.html>`_.

.. note::

    The ``CONCURRENTLY`` option is not supported inside a transaction (see
    :ref:`non-atomic migration <non-atomic-migrations>`).

Adding constraints without enforcing validation
===============================================

PostgreSQL supports the ``NOT VALID`` option with the ``ADD CONSTRAINT``
statement to add check constraints without enforcing validation on existing
rows. This option is useful if you want to skip the potentially lengthy scan of
the table to verify that all existing rows satisfy the constraint.

To validate check constraints created with the ``NOT VALID`` option at a later
point of time, use the
:class:`~django.contrib.postgres.operations.ValidateConstraint` operation.

See `the PostgreSQL documentation <https://www.postgresql.org/docs/current/
sql-altertable.html#SQL-ALTERTABLE-NOTES>`__ for more details.

.. class:: AddConstraintNotValid(model_name, constraint)

    Like :class:`~django.db.migrations.operations.AddConstraint`, but avoids
    validating the constraint on existing rows.

.. class:: ValidateConstraint(model_name, name)

    Scans through the table and validates the given check constraint on
    existing rows.

.. note::

    ``AddConstraintNotValid`` and ``ValidateConstraint`` operations should be
    performed in two separate migrations. Performing both operations in the
    same atomic migration has the same effect as
    :class:`~django.db.migrations.operations.AddConstraint`, whereas performing
    them in a single non-atomic migration, may leave your database in an
    inconsistent state if the ``ValidateConstraint`` operation fails.