mirror of https://github.com/django/django.git
81 lines
2.6 KiB
Plaintext
81 lines
2.6 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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.. versionadded:: 1.11
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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)
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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 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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.. admonition:: Support for column ordering on SQLite
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Column ordering is supported on SQLite 3.3.0+ and only for some database
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file formats. Refer to the `SQLite docs
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<https://www.sqlite.org/lang_createindex.html>`_ for specifics.
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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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.. versionadded:: 2.0
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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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