=============================

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.

.. admonition:: Restrictions

    Non-deterministic collations are supported only on PostgreSQL 12+.

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

===============================================

.. versionadded:: 4.0

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.