added tests and fix for unpickleable metadata in SortedDictWithMetadata

1 files changed, 11 insertions, 1 deletions

diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index 4519ab05..fcc0744a 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -22,7 +22,16 @@ class DictWithMetadata(dict):
     """
     A dict-like object, that can have additional properties attached.
     """
-    pass
+
+    def __getstate__(self):
+        """  Used by pickle (e.g., caching).
+             Overriden to remove metadata from the dict, since it shouldn't be pickled
+             and may in some instances be unpickleable.
+        """
+        # return an instance of the first dict in MRO that isn't a DictWithMetadata
+        for base in self.__class__.__mro__:
+            if not isinstance(base, DictWithMetadata) and isinstance(base, dict):
+                return base(self)
 
 
 class SortedDictWithMetadata(SortedDict, DictWithMetadata):
@@ -32,6 +41,7 @@ class SortedDictWithMetadata(SortedDict, DictWithMetadata):
     pass
 
 
+
 def _is_protected_type(obj):
     """
     True if the object is a native datatype that does not need to