Support Q expressions that contain subquery expressions

[CelestialGuru]

Fixes bug when using Exists subqueries which are or-ed together:

SomeModel.objects.filter(
   Exists(RelatedModelA.objects.filter(some_model=OuterRef("pk"))
   | Exists(RelatedModelB.objects.filter(some_model=OuterRef("pk"))
)

This is done usually for performance reasons, but it is a valid queryset. Exist instances ored together like this creates a Q instance, but the children are not themselves Q instances. They are Exists instances.

Fixed #323

[j-antunes]

Thanks for opening a PR. Could you add the following:

• A unit test to cover your changes
• In your PR you change else to an elif, could you add another else so that in case none of the conditions are met, it will raise an exception or return something else.
  Thank you

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.50%. Comparing base (0d820d0) to head (6372ce1).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #572      +/-   ##
==========================================
+ Coverage   75.40%   75.50%   +0.09%     
==========================================
  Files          21       21              
  Lines        1342     1343       +1     
  Branches      211      212       +1     
==========================================
+ Hits         1012     1014       +2     
  Misses        257      257              
+ Partials       73       72       -1     

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[Copilot]

Pull request overview

This PR fixes a bug in the polymorphic query translation logic where Q expressions containing subquery expressions (like Exists) were not handled correctly. When Exists subqueries are combined using the | (OR) operator, Django creates a Q object with Exists instances as children, but the old code incorrectly assumed all non-tuple/list children of Q objects were themselves Q objects and attempted to recursively process them.

Key changes:

• Modified Q object tree traversal to explicitly check if children are Q objects before recursing
• Added comprehensive test coverage for the Exists subquery scenario with multiple test cases
• Added related_name to model field to support the new test queries

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
src/polymorphic/query_translate.py	Fixed Q object traversal to only recurse on Q children, not all non-tuple children
src/polymorphic/tests/test_orm.py	Added comprehensive test for Exists subqueries combined with OR operator
src/polymorphic/tests/models.py	Added related_name="inline_bs" to InlineModelB.plain_a field for test support
src/polymorphic/tests/migrations/0001_initial.py	Updated migration to reflect model changes
docs/changelog.rst	Added changelog entry (currently commented out)

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[bckohan]

This fixes a real bug - I have added tests. Thank you!

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

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