Fix related serializers with source argument that resolves to a callable

rest_framework/serializers.py

@@ -277,6 +277,9 @@ class BaseSerializer(Field):
         """
         obj = getattr(obj, self.source or field_name)
 
+        if is_simple_callable(obj):
+            obj = obj()
+
         # If the object has an "all" method, assume it's a relationship
         if is_simple_callable(getattr(obj, 'all', None)):
             return [self.to_native(item) for item in obj.all()]

rest_framework/tests/models.py

@@ -127,6 +127,9 @@ class ActionItem(RESTFrameworkModel):
 class BlogPost(RESTFrameworkModel):
     title = models.CharField(max_length=100)
 
+    def get_first_comment(self):
+        return self.blogpostcomment_set.all()[0]
+
 
 class BlogPostComment(RESTFrameworkModel):
     text = models.TextField()

rest_framework/tests/serializer.py

@@ -488,6 +488,7 @@ class ManyRelatedTests(TestCase):
             title = serializers.CharField()
             comments = BlogPostCommentSerializer(source='blogpostcomment_set')
 
+        self.comment_serializer_class = BlogPostCommentSerializer
         self.serializer_class = BlogPostSerializer
 
     def test_reverse_relations(self):
@@ -506,6 +507,23 @@ class ManyRelatedTests(TestCase):
 
         self.assertEqual(serializer.data, expected)
 
+    def test_callable_source(self):
+        post = BlogPost.objects.create(title="Test blog post")
+        post.blogpostcomment_set.create(text="I love this blog post")
+
+        class ExtendedBlogPostSerializer(self.serializer_class):
+            first_comment = self.comment_serializer_class(source='get_first_comment')
+
+        serializer = ExtendedBlogPostSerializer(post)
+        expected = {
+            'title': 'Test blog post',
+            'comments': [
+                {'text': 'I love this blog post'}
+            ],
+            'first_comment': {'text': 'I love this blog post'}
+        }
+        self.assertEqual(serializer.data, expected)
+
 
 # Test for issue #324
 class BlankFieldTests(TestCase):