Design for a chat app using Core Data

Question

I\'m writing a chat app and I\'m in the process of changing my db to use Core Data. I currently use sqlite directly but I want to take advantage of iCloud feature so I\'m switch

Answer 1

First, your mental model is all wrong. You should not think of core data as a SQL database. Yes, most of the time it uses SQL, but it is merely an implementation detail. You should think in terms of object graphs.

Next, for your "50 items" issue, look at NSFetchRequest. You can tell it where to start (fetchOffset), and how many items to fetch (fetchLimit). There are other options for you as well. If your total number of items is relatively small, you can just fetch the entire array (and only fault so many at a time - see fetchBatchSize).

For your "join" consider how objects are related to each other, not database table joins. Unfortunately, I do not understand what you are trying to achieve with that part of the question. However, you can mimic "joined" tables by using the dot notation when forming your predicate.

EDIT

When you create a conversation object, you can include a to-many relationship to something like "participants" which would be a set of all the users that participated in that conversation. The inverse would also be a to-many relationship in "user" that contained all the conversations that user participated in (I assume your database has multiple users???).

So, to get all the conversations in which a particular user participated, you could do something like fetch on "Participant" with a predicate similar to "ALL participants.username = %@"