Fix unique together validation.

[kalekseev]

While building validator unique together fields were compared with declared field names instead of model field names

fixes #9700

closes #9710

[auvipy]

looks good to me

[browniebroke]

This test seems to cover 2 separate cases, both failing on 3.16. Would you mind spliting it up into 2 methods?

Suggested change

	def test_uniq_together_validation_uses_model_fields(self):
	def test_uniq_together_validation_uses_model_fields_method_field(self):

[browniebroke]

Do you know why race_name is not required here? If I run this test on 3.15.2, I get the following diff (actual with +):

 TestSerializer():
-    race_name = CharField(max_length=100)
+    race_name = CharField(max_length=100, required=True) 

Which is more what I would expect, as the model field is not blank-able:

django-rest-framework/tests/test_validators.py

Line 166 in 9a76378

race_name = models.CharField(max_length=100)

[kalekseev]

The field is still required in the serializer, it's just not explicitly passed as arg thus not presented in the repr. In master it's explicitly set in the wrongly executed code path

django-rest-framework/rest_framework/serializers.py

Line 1504 in 33d59fe

uniqueness_extra_kwargs[unique_constraint_name] = {'required': True}

[kalekseev]

It also possible to unify code related to get_unique_together_constraints, these two code blocks are basically the same

django-rest-framework/rest_framework/serializers.py

Lines 1600 to 1604 in 33d59fe

	for unique_together, queryset, condition_fields, condition in self.get_unique_together_constraints(self.Meta.model):
	# Skip if serializer does not map to all unique together sources
	unique_together_and_condition_fields = set(unique_together) | set(condition_fields)
	if not set(source_map).issuperset(unique_together_and_condition_fields):
	continue

django-rest-framework/rest_framework/serializers.py

Lines 1475 to 1478 in 33d59fe

	for unique_together_list, queryset, condition_fields, condition in self.get_unique_together_constraints(model):
	unique_together_list_and_condition_fields = set(unique_together_list) | set(condition_fields)
	if set(field_names).issuperset(unique_together_list_and_condition_fields):
	unique_constraint_names |= unique_together_list_and_condition_fields