1 files changed, 23 insertions, 4 deletions
diff --git a/django/db/models/base.py b/django/db/models/base.py
index cc03ae1252..29bbde5e6b 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -382,11 +382,18 @@ class ModelBase(type):
         return cls._meta.default_manager
 
 
-class ModelStateFieldsCacheDescriptor:
+class ModelStateCacheDescriptor:
+    """
+    Upon first access, replace itself with an empty dictionary on the instance.
+    """
+
+    def __set_name__(self, owner, name):
+        self.attribute_name = name
+
     def __get__(self, instance, cls=None):
         if instance is None:
             return self
-        res = instance.fields_cache = {}
+        res = instance.__dict__[self.attribute_name] = {}
         return res
 
 
@@ -398,7 +405,20 @@ class ModelState:
     # explicit (non-auto) PKs. This impacts validation only; it has no effect
     # on the actual save.
     adding = True
-    fields_cache = ModelStateFieldsCacheDescriptor()
+    fields_cache = ModelStateCacheDescriptor()
+    related_managers_cache = ModelStateCacheDescriptor()
+
+    def __getstate__(self):
+        state = self.__dict__.copy()
+        if 'fields_cache' in state:
+            state['fields_cache'] = self.fields_cache.copy()
+        # Manager instances stored in related_managers_cache won't necessarily
+        # be deserializable if they were dynamically created via an inner
+        # scope, e.g. create_forward_many_to_many_manager() and
+        # create_generic_related_manager().
+        if 'related_managers_cache' in state:
+            state['related_managers_cache'] = {}
+        return state
 
 
 class Model(metaclass=ModelBase):
@@ -552,7 +572,6 @@ class Model(metaclass=ModelBase):
         """Hook to allow choosing the attributes to pickle."""
         state = self.__dict__.copy()
         state['_state'] = copy.copy(state['_state'])
-        state['_state'].fields_cache = state['_state'].fields_cache.copy()
         return state
 
     def __setstate__(self, state):