How to implement parent entity for core data

Question

Hi there.
I am starting a document-based Core Data application (Cocoa) and developed the following data model;
The 'invoice' entity is a parent entity of 'items', because ideally I would want there to be many items for each invoice. I guess my first point here is - is what I am trying to do going to be achieved using this method?
If so, I have been trying several ways in Interface Builder to sort out how to implement this structure with cocoa bindings. I have made a Core Data app before, just with one entity. So this time, I have two separate instances of NSArrayController's connected to tables with relevant columns. I can add new 'invoice' entities fine, but I can't get corresponding 'items' to add.
I tried setting the Managed Object Context of the 'item' NSArrayController to this;
I thought this would resolve the issue, but I still have found no resolution to the problem.
If anyone done something similar to this, I'd appreciate any help
Thanks in advance,
Ricky.

Answer 1

Second, when you create a Core Data Document Based application, XCode generates the MyDocument class, derivating from NSPersistentDocument. This class is dedicated to maintain the Managed Object Model and the Managed Object Context of each document of your application.
There is only one Context and generally one Model for each Document.
In Interface Builder, the Managed Object Context must be bound to the managedObjectContext of the MyDocument instance: it's the File's owner of the myDocument.xib Nib file.
It's not the case in your Nib File where the Managed Object Context is bound to the invoiceID of the Invoice Controller.
It's difficult to help you without an overall knowledge of your application, perhaps could you create an InvoiceItem Controller and bind its Content Set to the relationship of your invoice.