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Fixed #36075 -- Documented how to introspect composite primary keys.

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Document _meta.pk_fields and interactions between Field.primary_key and
CompositePrimaryKey.

Thanks Mariusz for the review.
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Simon Charette 2025-01-12 23:06:46 -05:00 • committed by Sarah Boyce
parent f2a1dcaa53
commit e580926d74
3 changed files with 105 additions and 10 deletions
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24
docs/ref/models/fields.txt
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@ -542,18 +542,20 @@ cross-site scripting attack.
If ``True``, this field is the primary key for the model.
If you don't specify ``primary_key=True`` for any field in your model, Django
will automatically add a field to hold the primary key, so you don't need to
set ``primary_key=True`` on any of your fields unless you want to override the
default primary-key behavior. The type of auto-created primary key fields can
be specified per app in :attr:`AppConfig.default_auto_field
<django.apps.AppConfig.default_auto_field>` or globally in the
:setting:`DEFAULT_AUTO_FIELD` setting. For more, see
If you don't specify ``primary_key=True`` for any field in your model and have
not defined a composite primary key, Django will automatically add a field to
hold the primary key. So, you don't need to set ``primary_key=True`` on any of
your fields unless you want to override the default primary-key behavior. The
type of auto-created primary key fields can be specified per app in
:attr:`AppConfig.default_auto_field <django.apps.AppConfig.default_auto_field>`
or globally in the :setting:`DEFAULT_AUTO_FIELD` setting. For more, see
:ref:`automatic-primary-key-fields`.
``primary_key=True`` implies :attr:`null=False <Field.null>` and
:attr:`unique=True <Field.unique>`. Only one primary key is allowed on an
object.
:attr:`unique=True <Field.unique>`. Only one field per model can set
``primary_key=True``. Composite primary keys must be defined using
:class:`CompositePrimaryKey` instead of setting this flag to ``True`` for all
fields to maintain this invariant.
The primary key field is read-only. If you change the value of the primary
key on an existing object and then save it, a new object will be created
@ -562,6 +564,10 @@ alongside the old one.
The primary key field is set to ``None`` when
:meth:`deleting <django.db.models.Model.delete>` an object.
.. versionchanged:: 5.2
The ``CompositePrimaryKey`` field was added.
``unique``
----------