# Τεκμηρίωση του Django - 3.2.11.dev

# Database migration operations

All of these operations are available from the `django.contrib.postgres.operations` module.

## 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 `HStoreField` by adding a migration with the `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;`.

Changed in Django 3.2:

In older versions, the pre-existence of the extension isn’t checked.

## `CreateExtension`

class `CreateExtension`(name)

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

  `name`

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

## `BloomExtension`

class `BloomExtension`
  New in Django 3.1.

  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.

## Managing collations using migrations

New in Django 3.2.

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 `CharField`, `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.

Restrictions

PostgreSQL 9.6 only supports the `'libc'` provider.

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 `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.

class `RemoveIndexConcurrently`(model_name, name)

  Like `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.

Σημείωση

The `CONCURRENTLY` option is not supported inside a transaction (see non-atomic migration).