fix(blank/unique): add default handling for blank=True field

rest_framework/serializers.py

@@ -1523,8 +1523,11 @@ def get_uniqueness_extra_kwargs(self, field_names, declared_fields, extra_kwargs
                 default = unique_constraint_field.default
             elif unique_constraint_field.null:
                 default = None
-            else:
-                default = empty
+            elif unique_constraint_field.blank:
+                if isinstance(unique_constraint_field, (models.CharField, models.TextField)):
+                    default = ''
+                else:
+                    default = empty
 
             if unique_constraint_name in model_fields:
                 # The corresponding field is present in the serializer

tests/test_validators.py

@@ -149,6 +149,14 @@ class Meta:
         unique_together = ('race_name', 'position')
 
 
+class BlankUniquenessTogetherModel(models.Model):
+    race_name = models.CharField(max_length=100, blank=True)
+    position = models.IntegerField()
+
+    class Meta:
+        unique_together = ('race_name', 'position')
+
+
 class NullUniquenessTogetherModel(models.Model):
     """
     Used to ensure that null values are not included when checking
@@ -176,6 +184,12 @@ class Meta:
         fields = '__all__'
 
 
+class BlankUniquenessTogetherSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = BlankUniquenessTogetherModel
+        fields = '__all__'
+
+
 class NullUniquenessTogetherSerializer(serializers.ModelSerializer):
     class Meta:
         model = NullUniquenessTogetherModel
@@ -461,6 +475,34 @@ def test_do_not_ignore_validation_for_null_fields(self):
         serializer = NullUniquenessTogetherSerializer(data=data)
         assert not serializer.is_valid()
 
+    def test_validation_for_provided_blank_fields(self):
+        BlankUniquenessTogetherModel.objects.create(
+            position=1
+        )
+        data = {
+            'race_name': '',
+            'position': 1
+        }
+        serializer = BlankUniquenessTogetherSerializer(data=data)
+        assert not serializer.is_valid()
+
+    def test_validation_for_missing_blank_fields(self):
+        BlankUniquenessTogetherModel.objects.create(
+            position=1
+        )
+        data = {
+            'position': 1
+        }
+        serializer = BlankUniquenessTogetherSerializer(data=data)
+        assert not serializer.is_valid()
+
+    def test_ignore_validation_for_missing_blank_fields(self):
+        data = {
+            'position': 1
+        }
+        serializer = BlankUniquenessTogetherSerializer(data=data)
+        assert serializer.is_valid(), serializer.errors
+
     def test_ignore_validation_for_unchanged_fields(self):
         """
         If all fields in the unique together constraint are unchanged,
@@ -589,6 +631,21 @@ class Meta:
         ]
 
 
+class UniqueConstraintBlankModel(models.Model):
+    title = models.CharField(max_length=100, blank=True)
+    age = models.IntegerField()
+    tag = models.CharField(max_length=100, blank=True)
+
+    class Meta:
+        constraints = [
+            # Unique constraint on one required field (age) and one blank field (tag)
+            models.UniqueConstraint(
+              name='unique_constraint', 
+              fields=('age', 'tag'), 
+              condition=~models.Q(models.Q(title='') & models.Q(tag='True')))
+          ]
+
+
 class UniqueConstraintReadOnlyFieldModel(models.Model):
     state = models.CharField(max_length=100, default="new")
     position = models.IntegerField()
@@ -642,6 +699,12 @@ class Meta:
         fields = '__all__'
 
 
+class UniqueConstraintBlankSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = UniqueConstraintBlankModel
+        fields = ('title', 'age', 'tag')
+
+
 class UniqueConstraintNullableSerializer(serializers.ModelSerializer):
     class Meta:
         model = UniqueConstraintNullableModel
@@ -755,6 +818,12 @@ def test_single_field_uniq_validators(self):
         ids_in_qs = {frozenset(v.queryset.values_list('id', flat=True)) for v in validators if hasattr(v, "queryset")}
         assert ids_in_qs == {frozenset([1]), frozenset([3])}
 
+    def test_blank_unique_constraint_fields_are_not_required(self):
+        serializer = UniqueConstraintBlankSerializer(data={'age': 25})
+        self.assertTrue(serializer.is_valid(), serializer.errors)
+        result = serializer.save()
+        self.assertIsInstance(result, UniqueConstraintBlankModel)
+
     def test_nullable_unique_constraint_fields_are_not_required(self):
         serializer = UniqueConstraintNullableSerializer(data={'title': 'Bob'})
         self.assertTrue(serializer.is_valid(), serializer.errors)