Fixed Datastructures so instances are a Document or EmbeddedDocument (#363)

docs/changelog.rst

@@ -5,6 +5,7 @@ Changelog
 
 Changes in 0.8.2
 ================
+- Fixed Datastructures so instances are a Document or EmbeddedDocument (#363)
 - Improved cascading saves write performance (#361)
 - Fixed amibiguity and differing behaviour regarding field defaults (#349)
 - ImageFields now include PIL error messages if invalid error (#353)

mongoengine/base/datastructures.py

@@ -13,7 +13,11 @@ class BaseDict(dict):
     _name = None
 
     def __init__(self, dict_items, instance, name):
-        self._instance = weakref.proxy(instance)
+        Document = _import_class('Document')
+        EmbeddedDocument = _import_class('EmbeddedDocument')
+
+        if isinstance(instance, (Document, EmbeddedDocument)):
+            self._instance = weakref.proxy(instance)
         self._name = name
         return super(BaseDict, self).__init__(dict_items)
 
@@ -80,7 +84,11 @@ class BaseList(list):
     _name = None
 
     def __init__(self, list_items, instance, name):
-        self._instance = weakref.proxy(instance)
+        Document = _import_class('Document')
+        EmbeddedDocument = _import_class('EmbeddedDocument')
+
+        if isinstance(instance, (Document, EmbeddedDocument)):
+            self._instance = weakref.proxy(instance)
         self._name = name
         return super(BaseList, self).__init__(list_items)