Merge 45235e19cb into b1035b2a87

rest_framework/fields.py

@@ -64,7 +64,7 @@ def is_simple_callable(obj):
     return len_args <= len_defaults
 
 
-def get_attribute(instance, attrs):
+def get_attribute(instance, attrs, required=True):
     """
     Similar to Python's built in `getattr(instance, attr)`,
     but takes a list of nested attributes, instead of a single attribute.
@@ -82,6 +82,12 @@ def get_attribute(instance, attrs):
                 instance = getattr(instance, attr)
         except ObjectDoesNotExist:
             return None
+        # RelatedObjectDoesNotExist inherits from both ObjectDoesNotExist and
+        # AttributeError, so ObjectDoesNotExist has to come first
+        except (AttributeError, KeyError):
+            if not required:
+                raise SkipField
+            raise
         if is_simple_callable(instance):
             try:
                 instance = instance()

rest_framework/relations.py

@@ -154,7 +154,7 @@ class RelatedField(Field):
                 pass
 
         # Standard case, return the object instance.
-        return get_attribute(instance, self.source_attrs)
+        return get_attribute(instance, self.source_attrs, self.required)
 
     @property
     def choices(self):

tests/test_relations_pk.py

@@ -340,6 +340,18 @@ class PKForeignKeyTests(TestCase):
         serializer = NullableForeignKeySourceSerializer()
         self.assertEqual(serializer.data['target'], None)
 
+    def test_foreign_key_not_required(self):
+        """
+        Let's say we wanted to fill the non-nullable model field inside
+        Model.save(), we would make it empty and not required.
+        """
+        class ModelSerializer(ForeignKeySourceSerializer):
+            class Meta(ForeignKeySourceSerializer.Meta):
+                extra_kwargs = {'target': {'required': False}}
+        serializer = ModelSerializer(data={'name': 'test'})
+        serializer.is_valid(raise_exception=True)
+        self.assertNotIn('target', serializer.data)
+
 
 class PKNullableForeignKeyTests(TestCase):
     def setUp(self):