Fix TypeError in RelatedField.get_choices() when to_representation returns unhashable type

[LeSingh1]

Summary

Fixes #5141.

When a user subclasses RelatedField and overrides to_representation() to return an unhashable type (e.g. a dict), visiting the endpoint in the Browsable API raises:

TypeError: unhashable type: 'dict'
  File "rest_framework/relations.py", in get_choices
    self.to_representation(item): self.display_value(item) for item in queryset

This happens because get_choices() uses the return value of to_representation() directly as a dictionary key, which requires it to be hashable.

Fix

Wrap the key in str() before inserting into the dict:

# Before
return {
    self.to_representation(item): self.display_value(item) for item in queryset
}

# After
return {
    str(self.to_representation(item)): self.display_value(item) for item in queryset
}

This is safe because:

• The choices dict keys are used as HTML <option value="..."> values, which are always strings in HTML.
• iter_options() uses these keys as option.value for the Browsable API select widget — string values are correct here.
• The existing behaviour for all built-in RelatedField subclasses is unchanged, since str() on an int (pk), str, or Hyperlink returns the same value.

Reproduction

from rest_framework import serializers

class MyRelatedField(serializers.RelatedField):
    def to_representation(self, obj):
        return {'id': obj.pk}  # unhashable dict

class MySerializer(serializers.Serializer):
    related_field = MyRelatedField(read_only=True)

Before this fix, visiting this endpoint in the Browsable API raises TypeError: unhashable type: 'dict'. After this fix it renders correctly.

[auvipy]

the tests are failing

[Copilot]

🟡 Changes recommended

Narrow the TypeError handling so display_value() is computed once and its errors are not misclassified.

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

Pull request overview

Fixes Browsable API failures when related-field representations are unhashable.

Changes:

• Falls back to string keys for unhashable representations.
• Adds regression and compatibility tests.

File summaries

File	Description
rest_framework/relations.py	Handles unhashable choice keys. Moderate issue: the broad try can misclassify and repeat display_value() errors.
tests/test_relations.py	Tests unhashable and existing hashable behavior.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

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[Copilot]

🟡 Changes recommended

The import-blocking indentation error and overly broad TypeError handling must be fixed.

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

Review details

Suppressed comments (3)

Previously missed (1) — in code that hasn't changed since the last review.

rest_framework/relations.py:208

• Catching TypeError around the whole insertion also swallows errors raised by a hashable key's equality comparison during a collision, incorrectly treating that key as unhashable. Probe hash(value) separately, then let unrelated insertion errors propagate.

tests/test_relations.py:528

• This constructs a read-only field and then manually adds a queryset, bypassing the constructor invariant that read-only relational fields must not have querysets. Read-only fields are also excluded from HTML forms, so this does not model the reported Browsable API path; use a supported writable field configuration instead.

        field = DictRelatedField(read_only=True)
        field.queryset = queryset

tests/test_relations.py:544

• This preservation assertion contradicts the PR description's advertised unconditional str(...) conversion. Preserving non-string RelatedField.choices keys is an established compatibility requirement from #4379, so the implementation and test are appropriate, but the PR description should be updated to describe conditional stringification rather than claiming every key is converted.

        # Keys should remain ints (not stringified), preserving existing behavior
        assert list(choices.keys()) == [1, 2]

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced