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Fixed #31502 -- Documented Model._state.db and Model._state.adding

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Tim Park 2020-07-05 21:30:00 -07:00 committed by Carlton Gibson
parent af2b3fee08
commit 697e59d5cf
1 changed files with 19 additions and 1 deletions
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20
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. to each of the missing fields.
In addition to creating the new model, the ``from_db()`` method must set the 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 Below is an example showing how to record the initial values of fields that
are loaded from the database:: are loaded from the database::
@ -853,3 +853,21 @@ Other attributes
class to identify the class of object that could not be found and to allow 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 you to catch a particular model class with ``try/except``. The exception is
a subclass of :exc:`django.core.exceptions.ObjectDoesNotExist`. 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.