#35671: Field.null=False on string-based fields behaves inconsistently with the
typical usage of Field.null.
-------------------------------------+-------------------------------------
Reporter: Clifford Gama | Type: Bug
Status: new | Component: Database
| layer (models, ORM)
Version: 5.1 | Severity: Normal
Keywords: Field.null; | Triage Stage:
IntegrityError; | Unreviewed
NotNullConstraint; Field.default |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
When `Field.null=False` and `Field.default` is not set for string-based
fields—such as `CharField`, `TextField`, and `SlugField`—`Field.null` does
not raise the expected `IntegrityError: NOT NULL constraint failed` when a
value is not provided for the field.
Django saves empty strings for these fields, and since the database does
not (always?) interpret an empty string as NULL, they are accepted without
raising the `IntegrityError`. This behavior is not clearly documented and
is inconsistent with the typical usage of `Field.null` as a NOT NULL
constraint.
The
[documentation](https://docs.djangoproject.com/en/5.1/ref/models/fields/#django.db.models.Field.null)
on `Field.null` specifies:
> Avoid using null on string-based fields such as CharField and TextField.
If a string-based field has null=True, that means it has two possible
values for “no data”: NULL and the empty string. In most cases, it’s
redundant to have two possible values for “no data;” the Django convention
is to use the empty string, not NULL.
What is not specified here or in the documentation for `Field.default` is
that Django effectively sets the empty string as the default for these
string-based fields when none is provided. If you wish to truly disallow
empty values for those fields, you need to set `Field.default=None` and
`null=False`.
Since Django relies on the database to raise `IntegrityError`s when a
required field is not provided, it is inconsistent that Django does not
treat the empty string as “no data” (i.e., NULL) in this context or that
they use the empty string as “no data” when the database will interpret it
as actual data.
The issue is particularly evident when a model instance is created using
the model Manager's `create()` and `get_or_create()` methods or by direct
instantiation.
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Ticket URL: <https://code.djangoproject.com/ticket/35671>
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