# Django 4.2.11 documentation

# 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;`.

## `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

  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

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(
                "case_insensitive",
                provider="icu",
                locale="und-u-ks-level2",
                deterministic=False,
            ),
            ...,
        ]

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 `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.

Note

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

## 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 `ValidateConstraint` operation.

See the PostgreSQL documentation for more details.

class AddConstraintNotValid(model_name, constraint)

  Like `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 `AddConstraint`, whereas performing them in a single non-atomic migration, may leave your database in an inconsistent state if the `ValidateConstraint` operation fails.