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

Signed-off-by: Sergei Shishov <sshishov.sshishov@gmail.com>

Author: sshishov

rest_framework/serializers.py

@@ -1496,6 +1496,8 @@ def get_uniqueness_extra_kwargs(self, field_names, declared_fields, extra_kwargs
                 default = unique_constraint_field.default
             elif unique_constraint_field.null:
                 default = None
+            elif unique_constraint_field.blank:
+                default = ''
             else:
                 default = empty
 

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,