Ternary relationships in coreData

Question

Lets say I have entities Article, Page and Category. I want entity Article to have a relationship like this. Article (A1) has a category (C1) for page (P1), but I want the same article (A1) to have a category (C2) for another page (P2).

How do I model this in coreData? I'm guessing maybe one of these relationships doesn't have to implement its inverse relationship, but I'm not sure about that. Any ideas?

Answer 1

Why not have the page entity keep track of it's category?

You could then provide a method on article that loops through all the page's and returns an NSSet of category's. If this was to be used often you could consider caching the result

Update

                      +----------+
                      | Category |              
                      +----------+
                            |
                            V
+---------+         +--------------+         +------+
| Article | <---->> | CategoryPage | <<----> | Page |
+---------+         +--------------+         +------+

• An article can have many pages through category_page
• A page can belong to many articles through category_page

I don't think you can simply do

+---------+         +------+
| Article | <<--->> | Page |
+---------+         +------+

because you also need the category information