保存上下文后，快速设置核心数据中的关系

Working with a core data model and I am still new this. Right now I have a view controller that saves the relationship between 2 entities and it stays fine until I have to add another relationship into the primary core data entity. When I do this the relationship between the initial 2 relationships breaks and the tableview is no longer able to present the relationship and thus crashes. I know in order to set the relationship I need to insert it into the already existing context but how do I actually go about that without clearing out the previously set relationhip?Working with a core data model and I am still n