Clarify behavior for Field.null=False on string-based fields

[Clifford Gama]

My concern is with the usage of Field.null=False, which differs from its expected practical application, rather than just its technical function.

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 IntegrityErrors 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.

[Sarah Boyce]

I don't think we can change the behavior here as this would be a breaking change and I think it makes sense that given a field which cannot be null, but can be a blank string, without a default set, it defaults to a blank string

But I agree that this is not clear in the docs and we can make an update there

Note, this is about how given a model:

class StringModel(Model):
    field = models.CharField(blank=False, null=False)

the value for StringModel().field is "", which is determined by the property Field._get_default

[Clifford Gama]

Hi Sarah!

Thank you for accepting this ticket and for clarifying, in the description, what needs to be done.

[Clifford Gama]

I have made the relevant additions in the documentation. You can view my progress on the branch here: [ticket_35671](​https://github.com/cliff688/django/tree/ticket_35671)

[Sarah Boyce <42296566+sarahboyce@…>]

In ca131898:

Fixed #35671 -- Clarified string-based fields behavior when null=False.