Removed use of _get_subclasses favouring get_document

_get_subclasses not actually required and causes issues
where Base Classes aren't imported but dont actually
need to be.

Fixes #271

mongoengine/base.py

@@ -845,21 +845,6 @@ class BaseDocument(object):
         """
         return cls._meta.get('collection', None)
 
-    @classmethod
-    def _get_subclasses(cls):
-        """Return a dictionary of all subclasses (found recursively).
-        """
-        try:
-            subclasses = cls.__subclasses__()
-        except:
-            subclasses = cls.__subclasses__(cls)
-
-        all_subclasses = {}
-        for subclass in subclasses:
-            all_subclasses[subclass._class_name] = subclass
-            all_subclasses.update(subclass._get_subclasses())
-        return all_subclasses
-
     @classmethod
     def _from_son(cls, son):
         """Create an instance of a Document (subclass) from a PyMongo SON.
@@ -877,16 +862,7 @@ class BaseDocument(object):
 
         # Return correct subclass for document type
         if class_name != cls._class_name:
-            subclasses = cls._get_subclasses()
-            if class_name not in subclasses:
-                # Type of document is probably more generic than the class
-                # that has been queried to return this SON
-                raise NotRegistered("""
-                        `%s` has not been registered in the document registry.
-                        Importing the document class automatically registers it,
-                        has it been imported?
-                    """.strip() % class_name)
-            cls = subclasses[class_name]
+            cls = get_document(class_name)
 
         changed_fields = []
         for field_name, field in cls._fields.items():

mongoengine/document.py

@@ -162,11 +162,10 @@ class Document(BaseDocument):
 
         doc = self.to_mongo()
 
-        created = '_id' in doc
-        creation_mode = force_insert or not created
+        created = force_insert or '_id' not in doc
         try:
             collection = self.__class__.objects._collection
-            if creation_mode:
+            if created:
                 if force_insert:
                     object_id = collection.insert(doc, safe=safe, **write_options)
                 else:
@@ -194,7 +193,7 @@ class Document(BaseDocument):
         self[id_field] = self._fields[id_field].to_python(object_id)
 
         self._changed_fields = []
-        signals.post_save.send(self.__class__, document=self, created=creation_mode)
+        signals.post_save.send(self.__class__, document=self, created=created)
 
     def cascade_save(self, *args, **kwargs):
         """Recursively saves any references / generic references on an object"""