Question

I’ve taught myself Obj-C, and have been self-teaching Cocoa, but adding Core Data to my program has given me nothing but a huge headache, thanks to me needing extensive custom logic. Here are a couple of the questions that are driving me insane.

1. What if I want a Managed Object to own another Managed Object? It seems if I give it a to-many relationship, the owned object will simply be shared by various masters, but I want each Owner to have its own.

2. If I subclass an NSManagedObject, can I make simple calls to the Array Controller to remove or copy instances of ManagedObject, and assume those will be translated into the Core Data model?

3. If I want to programmatically edit the properties of a ManagedObject, can I get away with mere KVC calls to the Array Controller? What’s all this talk about NSPredicate an NSFetchRequest to the NSManagedObjectContext from the NSManagedDataStoreDrivingMeCrazy? Can I make an NSFetchRequest that filters the relationships of an object currently selected in a table view?

4. Once I use a fetch request to get a group of objects, how do I go about querying their relations? Does that require a whole other FetchRequest, Predicate, and so forth? Isn’t Core Data supposed to be easier? Am I missing something?

Answer 1

1. An entity is similar to a class–it’s a blueprint for a managed object that will be instantiated later. Each managed object will have its own attributes and relationships to configure.

2. You can definitely insert and delete managed objects. You might have to do some code to support copying, but I am not sure.

3. Yes, the properties (attributes and relationships) of managed objects support KVC (and KVO and bindings).

4. You can access the object or set of objects simply by using the relationship name that you define in the model (no additional fetch or logic is required).