Fix UniqueConstraint validation with conditional fields (#9707) by majidkhazaei · Pull Request #10021 · encode/django-rest-framework

majidkhazaei · 2026-08-13T14:00:29Z

This is a rebased and conflict-resolved version of PR #9744.

Changes:

Added get_referenced_base_fields_from_q helper to rest_framework/compat.py
Fixed test indentation issues (moved test methods inside the correct class)
All 67 tests in tests/test_validators.py are passing

Resolves #9707
Supersedes #9744 (with resolved conflicts)

When using Django's UniqueConstraint with conditions that reference other fields,
DRF now correctly applies UniqueTogetherValidator instead of UniqueValidator.

…ogether validator

- Add helper function for extracting fields from Q objects - Move test methods inside TestUniquenessTogetherValidation class - All 67 tests passing Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

This PR fixes DRF’s ModelSerializer uniqueness validation for Django UniqueConstraint objects whose condition references additional model fields, ensuring DRF uses serializer-level UniqueTogetherValidator (with condition-awareness) instead of an incorrect field-level UniqueValidator.

Changes:

Add get_referenced_base_fields_from_q() compatibility helper and use it to detect fields referenced by UniqueConstraint.condition.
Update uniqueness validator selection so single-field constraints with distinct condition fields are validated via UniqueTogetherValidator.
Extend validator test coverage and document the UniqueConstraint-with-conditions behavior.

Reviewed changes

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

Show a summary per file

File	Description
`rest_framework/compat.py`	Adds helper to extract referenced base fields from `Q` conditions.
`rest_framework/utils/field_mapping.py`	Skips field-level `UniqueValidator` when condition references additional fields.
`rest_framework/serializers.py`	Treats certain single-field conditional `UniqueConstraint`s as “unique-together” for serializer-level validation.
`tests/test_validators.py`	Adds/adjusts tests for conditional-field uniqueness behavior and expected validator placement.
`docs/api-guide/validators.md`	Documents how DRF handles `UniqueConstraint` conditions.

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+            ]
+
+
+## Updating nested serializers


…eferenced_base_fields

peterthomassen · 2026-08-17T17:54:00Z

I find the whole conditional uniqueness stuff confusing and don't have the conceptual clarity in my head atm to give this a solid review (I'm sorry).

majidkhazaei · 2026-08-31T13:00:50Z

Hi @browniebroke, just a quick follow-up on this PR.

The checks have been green for a while, and the branch is up to date. Whenever you have a chance, I’d really appreciate a review. If there’s anything I can adjust or clarify, please let me know.

Thanks!

Copilot

Pull request overview

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

auvipy · 2026-09-06T14:23:58Z

+                        yield (
+                            constraint.fields,
+                            model._default_manager,
+                            condition_fields,
+                            constraint.condition,


@majidkhazaei was this resolved ?

auvipy · 2026-08-31T15:19:27Z

+                        yield (
+                            constraint.fields,
+                            model._default_manager,
+                            condition_fields,


@majidkhazaei please crosscheck this and other open suggestions

Thanks @auvipy!

Yes, I'm currently reviewing all the suggestions from Copilot. I'll go through them one by one and apply the necessary fixes (especially the ones regarding empty constraint.fields and condition field changes).

I'll push the updates later today and let you know once they're ready for another look.

Appreciate your patience and guidance!

…t for custom messages, recheck condition field changes - Add check for empty constraint.fields in get_unique_together_constraints - Preserve original constraint object for custom violation messages/codes - Extend UniqueTogetherValidator to recheck when condition fields change - Add test for condition field change triggering revalidation All 68 tests passing.

majidkhazaei · 2026-09-01T10:24:42Z

Hi @auvipy and @browniebroke,

All three Copilot issues are now fixed:

✅ Empty constraint.fields skipped (expression-based constraints)
✅ Original constraint preserved for custom messages/codes
✅ Condition field changes now trigger revalidation

A new test was added for the condition field scenario. All 68 tests are passing.

PR is ready for final review and merge. Thanks! 🙏

auvipy · 2026-09-03T16:09:29Z

tried to fix a newly emerged merge conflict

majidkhazaei · 2026-09-06T12:12:46Z

All conflicts resolved, 76 tests passing, pre-commit checks green.
Ready for final review. Thanks!

Copilot

🟡 Changes recommended

Validation can be skipped for omitted or nullable condition fields, and the new transition test does not exercise the regression.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

Files reviewed: 6/6 changed files
Comments generated: 2
Review effort level: Balanced

auvipy · 2026-09-06T14:23:17Z

+            checked_values = [attrs.get(field_name) for field_name in checked_names]
        else:
            # Ignore validation if all field values are unchanged
            checked_values = [
-                attrs[field_name]
+                attrs.get(field_name)
                for field_name in checked_names
-                if attrs[field_name] != getattr(serializer.instance, field_name)
+                if attrs.get(field_name) != getattr(serializer.instance, field_name, None)


@majidkhazaei please cross check this and other open suggestions

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

nefrob and others added 4 commits August 13, 2026 16:08

chore: unique constraints with distinct condition fields use unique t…

8d796e8

…ogether validator

chore: add comments and improve tests

a2cc17a

test: correct assertions

867e9be

auvipy requested review from auvipy and a lite review from Copilot August 13, 2026 14:21

Copilot started reviewing on behalf of auvipy August 13, 2026 14:21 View session

Fix pre-commit formatting issues (isort and flake8)

d773cff

Copilot AI reviewed Aug 13, 2026

View reviewed changes

Comment thread docs/api-guide/validators.md Outdated

]

## Updating nested serializers

Comment thread rest_framework/compat.py Outdated

auvipy added this to the 3.18 milestone Aug 13, 2026

Apply Copilot suggestions: fix heading hierarchy and use Django's Q.r…

e8794dc

…eferenced_base_fields

majidkhazaei force-pushed the pr-9744 branch from ebeb52b to e8794dc Compare August 14, 2026 08:03

auvipy requested review from browniebroke and peterthomassen August 17, 2026 10:10

auvipy requested a balanced review from Copilot August 31, 2026 14:04

Copilot started reviewing on behalf of auvipy August 31, 2026 14:05 View session

auvipy removed the request for review from peterthomassen August 31, 2026 14:05

Copilot AI reviewed Aug 31, 2026

View reviewed changes

majidkhazaei force-pushed the pr-9744 branch from ec2a480 to 1be7064 Compare September 1, 2026 10:10

majidkhazaei force-pushed the pr-9744 branch from 1be7064 to 51b7897 Compare September 1, 2026 10:17

auvipy added 2 commits September 1, 2026 16:32

Merge branch 'main' into pr-9744

d49f7ee

Merge branch 'main' into pr-9744

54c7472

majidkhazaei added 2 commits September 4, 2026 10:22

Fix isort import ordering in serializers.py

93e84b8

Resolve merge conflicts with upstream/main in validators and tests

cbfead3

majidkhazaei force-pushed the pr-9744 branch from 73a6bb1 to cbfead3 Compare September 6, 2026 12:05

Merge branch 'main' into pr-9744

06a6057

auvipy requested a balanced review from Copilot September 6, 2026 14:08

auvipy added the Bug label Sep 6, 2026

Copilot started reviewing on behalf of auvipy September 6, 2026 14:08 View session

Copilot AI reviewed Sep 6, 2026

View reviewed changes

Refactor uniqueness validation test case

970392e

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

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