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Fixed #35659 -- Documented db_default behaviour before instances are saved. #18454

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Fixed #35659 -- Documented db_default behaviour before instances are saved. #18454

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e4ab2ce
Document db_default behavior in BooleanField
jcagado Aug 7, 2024
cd7d243
Reformatted .txt files using blacken-docs
jcagado Aug 7, 2024
7da55b0
Fixed formatting issues and spelling in fields.txt
jcagado Aug 7, 2024
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28 changes: 28 additions & 0 deletions docs/ref/models/fields.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -700,6 +700,34 @@ or :class:`~django.forms.NullBooleanSelect` if :attr:`null=True <Field.null>`.
The default value of ``BooleanField`` is ``None`` when :attr:`Field.default`
isn't defined.

.. note::

When using the ``db_default`` attribute, the field value will be an instance of ``DatabaseDefault`` before the instance is saved to the database. This means that a ``bool()`` evaluation of the field will not reflect the specified ``db_default`` value until the instance is saved.

For example:

.. code-block:: python

from django.db import models


class MyModel(models.Model):
my_field = models.BooleanField(db_default=False)


my_obj = MyModel()
print(bool(my_obj.my_field)) # True, which is unexpected.

my_obj.save()
print(bool(my_obj.my_field)) # False, as expected.

To ensure the field value reflects the desired default before saving, also set the ``default`` attribute:

.. code-block:: python

class MyModel(models.Model):
my_field = models.BooleanField(default=False, db_default=False)

``CharField``
-------------

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