From a8595a8eae2649b763f4882da643c1dc9183d6f1 Mon Sep 17 00:00:00 2001
From: Bruno Alla <browniebroke@users.noreply.github.com>
Date: Sat, 14 Dec 2024 09:08:22 +0000
Subject: [PATCH] Fix raising on nullable fields part of `UniqueConstraint`
 (#9531)

* Add test to reproduce problem with nullable fields part of a unique constraint

Ref #9378

* Simplify test case and add similar case for unique_together

* Add test for unique together in a better place

* Default nullable fields to null in unique constraints checks

* Remove redundant test and move other to more appropriate place
---
 rest_framework/serializers.py |  2 ++
 tests/test_validators.py      | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index b1b7b64774..f37bd3a3d6 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -1490,6 +1490,8 @@ def get_uniqueness_extra_kwargs(self, field_names, declared_fields, extra_kwargs
                 default = timezone.now
             elif unique_constraint_field.has_default():
                 default = unique_constraint_field.default
+            elif unique_constraint_field.null:
+                default = None
             else:
                 default = empty
 
diff --git a/tests/test_validators.py b/tests/test_validators.py
index 4bb8658d5b..9c1a0eac31 100644
--- a/tests/test_validators.py
+++ b/tests/test_validators.py
@@ -441,6 +441,14 @@ def test_ignore_validation_for_null_fields(self):
         serializer = NullUniquenessTogetherSerializer(data=data)
         assert serializer.is_valid()
 
+    def test_ignore_validation_for_missing_nullable_fields(self):
+        data = {
+            'date': datetime.date(2000, 1, 1),
+            'race_name': 'Paris Marathon',
+        }
+        serializer = NullUniquenessTogetherSerializer(data=data)
+        assert serializer.is_valid(), serializer.errors
+
     def test_do_not_ignore_validation_for_null_fields(self):
         # None values that are not on fields part of the uniqueness constraint
         # do not cause the instance to skip validation.
@@ -539,12 +547,30 @@ class Meta:
         ]
 
 
+class UniqueConstraintNullableModel(models.Model):
+    title = models.CharField(max_length=100)
+    age = models.IntegerField(null=True)
+    tag = models.CharField(max_length=100, null=True)
+
+    class Meta:
+        constraints = [
+            # Unique constraint on 2 nullable fields
+            models.UniqueConstraint(name='unique_constraint', fields=('age', 'tag'))
+        ]
+
+
 class UniqueConstraintSerializer(serializers.ModelSerializer):
     class Meta:
         model = UniqueConstraintModel
         fields = '__all__'
 
 
+class UniqueConstraintNullableSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = UniqueConstraintNullableModel
+        fields = ('title', 'age', 'tag')
+
+
 class TestUniqueConstraintValidation(TestCase):
     def setUp(self):
         self.instance = UniqueConstraintModel.objects.create(
@@ -611,6 +637,12 @@ def test_single_field_uniq_validators(self):
         ids_in_qs = {frozenset(v.queryset.values_list(flat=True)) for v in validators if hasattr(v, "queryset")}
         assert ids_in_qs == {frozenset([1]), frozenset([3])}
 
+    def test_nullable_unique_constraint_fields_are_not_required(self):
+        serializer = UniqueConstraintNullableSerializer(data={'title': 'Bob'})
+        self.assertTrue(serializer.is_valid(), serializer.errors)
+        result = serializer.save()
+        self.assertIsInstance(result, UniqueConstraintNullableModel)
+
 
 # Tests for `UniqueForDateValidator`
 # ----------------------------------