mirror of
https://github.com/django/django.git
synced 2024-11-18 07:26:04 +00:00
a906c98982
Thanks to Ian Foote, Mariusz Felisiak, Simon Charettes, and Markus Holtermann for comments and feedback.
136 lines
4.5 KiB
Plaintext
136 lines
4.5 KiB
Plaintext
=====================
|
|
Model index reference
|
|
=====================
|
|
|
|
.. module:: django.db.models.indexes
|
|
|
|
.. currentmodule:: django.db.models
|
|
|
|
Index classes ease creating database indexes. They can be added using the
|
|
:attr:`Meta.indexes <django.db.models.Options.indexes>` option. This document
|
|
explains the API references of :class:`Index` which includes the `index
|
|
options`_.
|
|
|
|
.. admonition:: Referencing built-in indexes
|
|
|
|
Indexes are defined in ``django.db.models.indexes``, but for convenience
|
|
they're imported into :mod:`django.db.models`. The standard convention is
|
|
to use ``from django.db import models`` and refer to the indexes as
|
|
``models.<IndexClass>``.
|
|
|
|
``Index`` options
|
|
=================
|
|
|
|
.. class:: Index(fields=(), name=None, db_tablespace=None, opclasses=(), condition=None)
|
|
|
|
Creates an index (B-Tree) in the database.
|
|
|
|
``fields``
|
|
----------
|
|
|
|
.. attribute:: Index.fields
|
|
|
|
A list or tuple of the name of the fields on which the index is desired.
|
|
|
|
By default, indexes are created with an ascending order for each column. To
|
|
define an index with a descending order for a column, add a hyphen before the
|
|
field's name.
|
|
|
|
For example ``Index(fields=['headline', '-pub_date'])`` would create SQL with
|
|
``(headline, pub_date DESC)``. Index ordering isn't supported on MySQL. In that
|
|
case, a descending index is created as a normal index.
|
|
|
|
.. versionchanged:: 2.1
|
|
|
|
Older versions don't accept a tuple.
|
|
|
|
``name``
|
|
--------
|
|
|
|
.. attribute:: Index.name
|
|
|
|
The name of the index. If ``name`` isn't provided Django will auto-generate a
|
|
name. For compatibility with different databases, index names cannot be longer
|
|
than 30 characters and shouldn't start with a number (0-9) or underscore (_).
|
|
|
|
``db_tablespace``
|
|
-----------------
|
|
|
|
.. attribute:: Index.db_tablespace
|
|
|
|
The name of the :doc:`database tablespace </topics/db/tablespaces>` to use for
|
|
this index. For single field indexes, if ``db_tablespace`` isn't provided, the
|
|
index is created in the ``db_tablespace`` of the field.
|
|
|
|
If :attr:`.Field.db_tablespace` isn't specified (or if the index uses multiple
|
|
fields), the index is created in tablespace specified in the
|
|
:attr:`~django.db.models.Options.db_tablespace` option inside the model's
|
|
``class Meta``. If neither of those tablespaces are set, the index is created
|
|
in the same tablespace as the table.
|
|
|
|
.. seealso::
|
|
|
|
For a list of PostgreSQL-specific indexes, see
|
|
:mod:`django.contrib.postgres.indexes`.
|
|
|
|
``opclasses``
|
|
-------------
|
|
|
|
.. attribute:: Index.opclasses
|
|
|
|
.. versionadded:: 2.2
|
|
|
|
The names of the `PostgreSQL operator classes
|
|
<https://www.postgresql.org/docs/current/static/indexes-opclass.html>`_ to use for
|
|
this index. If you require a custom operator class, you must provide one for
|
|
each field in the index.
|
|
|
|
For example, ``GinIndex(name='json_index', fields=['jsonfield'],
|
|
opclasses=['jsonb_path_ops'])`` creates a gin index on ``jsonfield`` using
|
|
``jsonb_path_ops``.
|
|
|
|
``opclasses`` are ignored for databases besides PostgreSQL.
|
|
|
|
:attr:`Index.name` is required when using ``opclasses``.
|
|
|
|
``condition``
|
|
-------------
|
|
|
|
.. attribute:: Index.condition
|
|
|
|
.. versionadded:: 2.2
|
|
|
|
If the table is very large and your queries mostly target a subset of rows,
|
|
it may be useful to restrict an index to that subset. Specify a condition as a
|
|
:class:`~django.db.models.Q`. For example, ``condition=Q(pages__gt=400)``
|
|
indexes records with more than 400 pages.
|
|
|
|
:attr:`Index.name` is required when using ``condition``.
|
|
|
|
.. admonition:: Restrictions on PostgreSQL
|
|
|
|
PostgreSQL requires functions referenced in the condition to be be marked as
|
|
IMMUTABLE. Django doesn't validate this but PostgreSQL will error. This
|
|
means that functions such as :ref:`date-functions` and
|
|
:class:`~django.db.models.functions.Concat` aren't accepted. If you store
|
|
dates in :class:`~django.db.models.DateTimeField`, comparison to
|
|
:class:`~datetime.datetime` objects may require the ``tzinfo`` argument
|
|
to be provided because otherwise the comparison could result in a mutable
|
|
function due to the casting Django does for :ref:`lookups <field-lookups>`.
|
|
|
|
.. admonition:: Restrictions on SQLite
|
|
|
|
SQLite `imposes restrictions <https://www.sqlite.org/partialindex.html>`_
|
|
on how a partial index can be constructed.
|
|
|
|
.. admonition:: Oracle
|
|
|
|
Oracle does not support partial indexes. Instead, partial indexes can be
|
|
emulated using functional indexes. Use a :doc:`migration
|
|
</topics/migrations>` to add the index using :class:`.RunSQL`.
|
|
|
|
.. admonition:: MySQL and MariaDB
|
|
|
|
The ``condition`` argument is ignored with MySQL and MariaDB as neither
|
|
supports conditional indexes.
|