Enforce uniqueness validation for relational fields

rest_framework/fields.py

@@ -224,6 +224,8 @@ class Field(object):
         """
         if self.default is empty:
             raise SkipField()
+        if is_simple_callable(self.default):
+            return self.default()
         return self.default
 
     def run_validation(self, data=empty):

rest_framework/utils/field_mapping.py

@@ -219,6 +219,9 @@ def get_relation_kwargs(field_name, relation_info):
             kwargs['required'] = False
         if model_field.null:
             kwargs['allow_null'] = True
+        if getattr(model_field, 'unique', False):
+            validator = UniqueValidator(queryset=model_field.model._default_manager)
+            kwargs['validators'] = [validator]
 
     return kwargs
 

tests/test_model_serializer.py

@@ -248,7 +248,7 @@ class TestRelationalFieldMappings(TestCase):
             TestSerializer():
                 id = IntegerField(label='ID', read_only=True)
                 foreign_key = PrimaryKeyRelatedField(queryset=ForeignKeyTargetModel.objects.all())
-                one_to_one = PrimaryKeyRelatedField(queryset=OneToOneTargetModel.objects.all())
+                one_to_one = PrimaryKeyRelatedField(queryset=OneToOneTargetModel.objects.all(), validators=[<UniqueValidator(queryset=RelationalModel.objects.all())>])
                 many_to_many = PrimaryKeyRelatedField(many=True, queryset=ManyToManyTargetModel.objects.all())
                 through = PrimaryKeyRelatedField(many=True, read_only=True)
         """)
@@ -287,7 +287,7 @@ class TestRelationalFieldMappings(TestCase):
             TestSerializer():
                 url = HyperlinkedIdentityField(view_name='relationalmodel-detail')
                 foreign_key = HyperlinkedRelatedField(queryset=ForeignKeyTargetModel.objects.all(), view_name='foreignkeytargetmodel-detail')
-                one_to_one = HyperlinkedRelatedField(queryset=OneToOneTargetModel.objects.all(), view_name='onetoonetargetmodel-detail')
+                one_to_one = HyperlinkedRelatedField(queryset=OneToOneTargetModel.objects.all(), validators=[<UniqueValidator(queryset=RelationalModel.objects.all())>], view_name='onetoonetargetmodel-detail')
                 many_to_many = HyperlinkedRelatedField(many=True, queryset=ManyToManyTargetModel.objects.all(), view_name='manytomanytargetmodel-detail')
                 through = HyperlinkedRelatedField(many=True, read_only=True, view_name='throughtargetmodel-detail')
         """)