fix(blank/unique): add default handling for blank=True field

[sshishov]

Description

This MR should fix the issue with blank=True field in UniqueTogether constraint. It should not become required all of a sudden.

Fixes #9750

[sshishov]

I have added tests similar to the tests added in #9531

[auvipy]

did you check this pr #9725 ?

[deepakangadi]

Can we split it into multiple assertions?

[Copilot]

Pull request overview

This PR fixes an issue where blank=True fields in unique_together constraints were incorrectly becoming required. The fix adds special handling for blank fields by setting their default value to an empty string, similar to how null=True fields default to None. This ensures that blank fields in uniqueness constraints remain optional while still properly validating uniqueness.

Key Changes

• Added default='' handling for blank fields in unique constraints in get_uniqueness_extra_kwargs
• Added comprehensive test coverage for both unique_together and UniqueConstraint with blank fields
• Tests verify that blank fields are not required, while still enforcing uniqueness validation

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
rest_framework/serializers.py	Added conditional logic to set default='' for blank fields in the uniqueness constraint handling, following the same pattern as null field handling
tests/test_validators.py	Added new test models (BlankUniquenessTogetherModel, UniqueConstraintBlankModel) and test cases to verify blank fields in uniqueness constraints are not required but still validate correctly

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[Copilot]

Consider adding a docstring to BlankUniquenessTogetherModel similar to NullUniquenessTogetherModel (lines 160-172) to explain the purpose and expected behavior of blank fields in unique_together constraints.

[Copilot]

The test names test_validation_for_missing_blank_fields and test_ignore_validation_for_missing_blank_fields are confusing because both refer to "missing blank fields" but have opposite expectations. Consider renaming to make the distinction clearer, such as test_validation_fails_for_duplicate_blank_defaults and test_validation_passes_when_no_duplicates.

[auvipy]

please also fix the merge conflicts

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

tests/test_validators.py:831

• This test module consistently uses plain assert statements; these new tests use self.assertTrue / self.assertIsInstance instead. For consistency and readability, switch these to assert serializer.is_valid(), serializer.errors and assert isinstance(result, ...) like the rest of the file.

    def test_blank_unique_constraint_fields_are_not_required(self):
        serializer = UniqueConstraintBlankSerializer(data={'age': 25})
        self.assertTrue(serializer.is_valid(), serializer.errors)
        result = serializer.save()
        self.assertIsInstance(result, UniqueConstraintBlankModel)

    def test_nullable_unique_constraint_fields_are_not_required(self):
        serializer = UniqueConstraintNullableSerializer(data={'title': 'Bob'})
        self.assertTrue(serializer.is_valid(), serializer.errors)
        result = serializer.save()
        self.assertIsInstance(result, UniqueConstraintNullableModel)

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[auvipy]

let see if tests passes now