Question

I’ve been trying to debug this for 2 hours, have to sleep. First, I’ve searched and found many similar posts with they keywords: many entities same type and this one:
Core Data: inverse relationship for two relationships with same type

But to no avail. Here’s what’s happening:
I have a data model with two types. For example, I have a Person, and that person can have 4 lists of emails. The email type is its own thing, so I make the person store 4 distinct sets (relationships) to each list.

Basically, when I retrieve one set, it grabs all of them. All 4 lists are now 1, and it doesn’t seem to matter how I set the inverses. Actually these changes somehow caused the entire thing to not save anything, all nil objects when downloaded. Previous to this, it worked fine (except for shoving all 4 lists into one set). All I updated was the data model for relationships. I may have exported the files in the wrong order, but do not know if that’s related.

I simply can’t find the keyword combination to find if someone’s asked this before. I don’t see how it wouldn’t come up, what I’m doing is basic abstraction. I keep thinking I overlooked one box.

To summarize, I have a person, and person has 2 lists. I add them similar to this:
person.friendEmailsList = downloadedEmailsFromFriends;
person.businessEmailsList = downloadedBusinessEmails;

so later, I access person.friendEmailsList (using the correct core data call, of course), and instead of getting just friends, I get everything… friends, businesses everything

Any suggestions would be appreciated

Answer 1

There are two possible solutions.

First, you can use the approach you use. Just make sure that you also have corresponding reverse relationships from the other entity. So if you have 2 relationships to the same entity, that entity needs 2 distinct relationships back. E.g.

Person.friendsLists --->> List
Person.businessLists --->> List

List.friendPerson ---> Person
List.businessPerson ---> Person

The more flexible approach would be to have the list have an extra attribute type (could be a number as some kind of enum).

typedef enum {Friend = 1, Business } ListType;

You could put this into your List.h file. Now, to access just friend lists you can do this:

NSSet *friendList = [person.lists filteredSetUsingPredicate:
       [NSPredicate predicateWithFormat:@"type = %@", @(Friend)]];

This might be a bit much to type, so you can simplify by putting an accessor method into your Person.m (declare it in .h):

-(NSSet*)friendsLists {
    return [person.lists filteredSetUsingPredicate:
       [NSPredicate predicateWithFormat:@"type = %@", @(Friend)]];
}

Now you can access the lists with the usual convenient person.friendsLists.