预加载，预填充，将数据导入现有CoreData存储（SQLite）

I am in front of following problem: I have a CoreData based IPhone app, which I already have prepopulated by adding a sqlite-db to the resources folder and copy it to the documents folder if not already there. BUT: When I have to update the app and added a new SQLite db and the user already has a populated db in his document folder, how can I import the new data of the entity-tables into the existing db in the users document folder?I am in front of following problem: I have a Co