django/docs/ref/models/indexes.txt

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=====================
Model index reference
=====================
.. module:: django.db.models.indexes
.. currentmodule:: django.db.models
.. versionadded:: 1.11
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)
Creates an index (B-Tree) in the database.
``fields``
----------
.. attribute:: Index.fields
A list 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.
.. admonition:: Support for column ordering on SQLite
Column ordering is supported on SQLite 3.3.0+ and only for some database
file formats. Refer to the `SQLite docs
<https://www.sqlite.org/lang_createindex.html>`_ for specifics.
``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 (_).
.. seealso::
For a list of PostgreSQL-specific indexes, see
:mod:`django.contrib.postgres.indexes`.