Question

I’m getting a Cocoa error 1570 while trying to store data in a core data object that has a to-many relationship.

There error from the log file:

2012-05-25 12:02:38.919 TestProject[5059:12e03]   DetailedError: {
    NSLocalizedDescription = "The operation couldn\U2019t be completed. (Cocoa error 1570.)";
    NSValidationErrorKey = conversation;
    NSValidationErrorObject = "<Messages: 0x933e190> (entity: Messages; id: 0x933e1d0 <x-coredata:///Messages/tF3A62C22-456B-41EB-B9A4-0BA1E6738A6337> ; data: {\n    conversation = nil;\n    conversationID = nil;\n    createdAt = nil;\n    messageID = nil;\n    nickname = nil;\n    originNetwork = nil;\n    text = nil;\n    timestamp = nil;\n    userImageURL = nil;\n})";
}

The specific relationship is Conversations<—>>Messages, or one conversation can have multiple messages, and each message belongs to exactly one conversation.

In my model, both of these NSManagedObjects are optional.

My question is, how do I properly store a message object in conversation?

I know it has something to do with sets, but I have yet to implement it properly.

Any and all specific or abstract code-snippets would be much appreciated!

Thanks!

Answer 1

It depends on whether you’re using NSManagedObject subclasses or not. If you are (I like to do this), you’d have a ASConversation and ASMessage class (prefixes being whatever), then you have Xcode auto-generate them for you, and you can use something like:

NSManagedObjectContext *moc;  // exists 
ASConversation *conv = 
    [NSEntityDescription insertNewObjectForEntityForName:@"Conversation" 
                                  inManagedObjectContext:moc];
// … set values on the conv
ASMessage *msg = 
    [NSEntityDescription insertNewObjectForEntityForName:@"Message" 
                                  inManagedObjectContext:moc];
// … set other parts of the message

[conv addMessagesObject:msg];

Provided you have the inverse relationship set up correctly from Message back to Conversation as a to-one, all should be set up for you when you send save to the moc.

If you don’t have subclasses, you’d have to use the generic way, a bit more of a pain IMHO.

// Assume conv and msg exist as above, but both are of NSManagedObject types
NSMutableSet *set = [conv mutableSetValueForKey:@"messages"];
// Changes to the above set are managed by Core Data for you.
[set addObject:msg];

Then save as before. Do check that you have optional also set on the relationship – cocoa error 1570 is “mandatory value not set” – but it can apply to relationships too.