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[3.1.x] Fixed #31502 -- Documented Model._state.db and Model._state.adding

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Backport of 697e59d5cf81e6c7e4a06ca98d6e3e16cea486dc from master
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Tim Park 2020-07-05 21:30:00 -07:00 committed by Carlton Gibson
parent 2160481066
commit dad6973629
1 changed files with 19 additions and 1 deletions
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docs/ref/models/instances.txt
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@ -81,7 +81,7 @@ fields are present, then ``values`` are guaranteed to be in the order
to each of the missing fields.
In addition to creating the new model, the ``from_db()`` method must set the
``adding`` and ``db`` flags in the new instance's ``_state`` attribute.
``adding`` and ``db`` flags in the new instance's :attr:`~Model._state` attribute.
Below is an example showing how to record the initial values of fields that
are loaded from the database::
@ -859,3 +859,21 @@ Other attributes
class to identify the class of object that could not be found and to allow
you to catch a particular model class with ``try/except``. The exception is
a subclass of :exc:`django.core.exceptions.ObjectDoesNotExist`.
``_state``
----------
.. attribute:: Model._state
The ``_state`` attribute refers to a ``ModelState`` object that tracks
the lifecycle of the model instance.
The ``ModelState`` object has two attributes: ``adding``, a flag which is
``True`` if the model has not been saved to the database yet, and ``db``,
a string referring to the database alias the instance was loaded from or
saved to.
Newly instantiated instances have ``adding=True`` and ``db=None``,
since they are yet to be saved. Instances fetched from a ``QuerySet``
will have ``adding=False`` and ``db`` set to the alias of the associated
database.