=============================
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(),
            ...
        ]

Creating the extension requires a database user with superuser privileges.
If the Django database user doesn't have superuser privileges, you'll have
to create the extension outside of Django migrations with a user that has
the appropriate privileges. 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 PostgreSQL extensions.

    .. attribute:: name

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

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

.. class:: BtreeGinExtension()

    Install the ``btree_gin`` extension.

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

.. class:: BtreeGistExtension()

    Install 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.

Index concurrent operations
===========================

.. versionadded:: 3.0

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>`).
