improve _created status when switch collection and db

mongoengine/document.py

@@ -477,7 +477,7 @@ class Document(BaseDocument):
             raise OperationError(message)
         signals.post_delete.send(self.__class__, document=self)
 
-    def switch_db(self, db_alias):
+    def switch_db(self, db_alias, keep_created=True):
         """
         Temporarily switch the database for a document instance.
 
@@ -499,12 +499,12 @@ class Document(BaseDocument):
         self._get_collection = lambda: collection
         self._get_db = lambda: db
         self._collection = collection
-        self._created = True
+        self._created = True if not keep_created else self._created
         self.__objects = self._qs
         self.__objects._collection_obj = collection
         return self
 
-    def switch_collection(self, collection_name):
+    def switch_collection(self, collection_name, keep_created=True):
         """
         Temporarily switch the collection for a document instance.
 
@@ -525,7 +525,7 @@ class Document(BaseDocument):
             collection = cls._get_collection()
         self._get_collection = lambda: collection
         self._collection = collection
-        self._created = True
+        self._created = True if not keep_created else self._created
         self.__objects = self._qs
         self.__objects._collection_obj = collection
         return self