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95 lines
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95 lines
3.0 KiB
Plaintext
=====================
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Model index reference
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=====================
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.. module:: django.db.models.indexes
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.. currentmodule:: django.db.models
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Index classes ease creating database indexes. They can be added using the
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:attr:`Meta.indexes <django.db.models.Options.indexes>` option. This document
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explains the API references of :class:`Index` which includes the `index
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options`_.
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.. admonition:: Referencing built-in indexes
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Indexes are defined in ``django.db.models.indexes``, but for convenience
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they're imported into :mod:`django.db.models`. The standard convention is
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to use ``from django.db import models`` and refer to the indexes as
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``models.<IndexClass>``.
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``Index`` options
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=================
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.. class:: Index(fields=(), name=None, db_tablespace=None, opclasses=())
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Creates an index (B-Tree) in the database.
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``fields``
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----------
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.. attribute:: Index.fields
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A list or tuple of the name of the fields on which the index is desired.
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By default, indexes are created with an ascending order for each column. To
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define an index with a descending order for a column, add a hyphen before the
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field's name.
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For example ``Index(fields=['headline', '-pub_date'])`` would create SQL with
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``(headline, pub_date DESC)``. Index ordering isn't supported on MySQL. In that
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case, a descending index is created as a normal index.
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.. versionchanged:: 2.1
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Older versions don't accept a tuple.
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``name``
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--------
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.. attribute:: Index.name
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The name of the index. If ``name`` isn't provided Django will auto-generate a
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name. For compatibility with different databases, index names cannot be longer
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than 30 characters and shouldn't start with a number (0-9) or underscore (_).
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``db_tablespace``
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-----------------
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.. attribute:: Index.db_tablespace
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The name of the :doc:`database tablespace </topics/db/tablespaces>` to use for
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this index. For single field indexes, if ``db_tablespace`` isn't provided, the
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index is created in the ``db_tablespace`` of the field.
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If :attr:`.Field.db_tablespace` isn't specified (or if the index uses multiple
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fields), the index is created in tablespace specified in the
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:attr:`~django.db.models.Options.db_tablespace` option inside the model's
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``class Meta``. If neither of those tablespaces are set, the index is created
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in the same tablespace as the table.
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.. seealso::
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For a list of PostgreSQL-specific indexes, see
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:mod:`django.contrib.postgres.indexes`.
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``opclasses``
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-------------
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.. attribute:: Index.opclasses
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.. versionadded:: 2.2
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The names of the `PostgreSQL operator classes
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<https://www.postgresql.org/docs/current/static/indexes-opclass.html>`_ to use for
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this index. If you require a custom operator class, you must provide one for
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each field in the index.
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For example, ``GinIndex(name='json_index', fields=['jsonfield'],
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opclasses=['jsonb_path_ops'])`` creates a gin index on ``jsonfield`` using
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``jsonb_path_ops``.
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``opclasses`` are ignored for databases besides PostgreSQL.
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:attr:`Index.name` is required when using ``opclasses``.
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