Merge pull request #2798 from Boomerangz/depth-should-reduce

Depth should reduce on nested ModelSerializer classes.

Author: tomchristie

rest_framework/serializers.py

@@ -1038,7 +1038,7 @@ def build_nested_field(self, field_name, relation_info, nested_depth):
         class NestedSerializer(ModelSerializer):
             class Meta:
                 model = relation_info.related_model
-                depth = nested_depth
+                depth = nested_depth - 1
 
         field_class = NestedSerializer
         field_kwargs = get_nested_relation_kwargs(relation_info)