Add nulls_distinct support to UniqueTogetherValidator

[mag123c]

Fixes #8409

This PR adds support for Django 5.0's nulls_distinct option in UniqueTogetherValidator.

Problem

When nulls_distinct=False is set on a UniqueConstraint, DRF's validator still skips validation for NULL values, causing integrity errors on databases like Oracle where NULLs can violate unique constraints.

Solution

• Extract nulls_distinct from UniqueConstraint in get_unique_together_constraints()
• Pass it to UniqueTogetherValidator.__init__
• When nulls_distinct=False, validate NULL values as potential duplicates

Changes

• rest_framework/serializers.py: Updated get_unique_together_constraints() to yield nulls_distinct
• rest_framework/validators.py: Added nulls_distinct parameter to UniqueTogetherValidator
• tests/test_validators.py: Added tests for nulls_distinct=False behavior (Django 5.0+)

Backward Compatibility

• nulls_distinct=None (default): Existing behavior preserved (skip NULL validation)
• Django < 5.0: Uses getattr() fallback, no breaking changes

[Copilot]

Pull request overview

This PR adds support for Django 5.0's nulls_distinct parameter to the UniqueTogetherValidator class in Django REST Framework. When nulls_distinct=False is set on a UniqueConstraint, the validator now properly treats NULL values as equal for uniqueness checks, preventing integrity errors on databases like Oracle where NULLs can violate unique constraints.

Changes:

• Modified get_unique_together_constraints() to extract and yield the nulls_distinct attribute from constraints
• Updated UniqueTogetherValidator to accept and handle the nulls_distinct parameter in validation logic
• Added comprehensive tests for the new functionality with Django 5.0+ version guards

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
rest_framework/serializers.py	Updated get_unique_together_constraints() to yield nulls_distinct from constraints and modified call sites to unpack the additional tuple element
rest_framework/validators.py	Added nulls_distinct parameter to UniqueTogetherValidator, updated validation logic to skip NULL checks when nulls_distinct=False, and modified __repr__() and __eq__() methods
tests/test_validators.py	Added test model with nulls_distinct=False constraint and comprehensive test cases for create operations and validator equality

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[auvipy]

please cross check the suggestion and see if they are right to go with

[mag123c]

@auvipy Reviewed all 5 Copilot suggestions.