title: What do you bind NSArrayController's Managed Object Context to in Xcode 4?
body: <p>I am trying to build an document-based application for beer reviewing that allows you to enter your notes. I have built the model in Core Data and the view in Interface Builder. Following some Xcode 3-based tutorials, I am told to connect the new NSArrayController to the managedObjectContext of File's Owner. If I try and do this in Xcode 4, a circled exclamation point comes up next to "Model Key Path" in the inspector for the NSArrayController.</p>
  
  <p>I can actually load the .xib file in Interface Builder in Xcode 3, make that connection, and then build it in Xcode 4 and it runs, but every field raises a validation error.</p>
  
  <p>The model has an entity named Scoresheet, which has a property named date, which is an NSDate. But if I link it to the value of an NSDatePicker and try to save it to disk, it says I have "multiple validation errors." How can <strong><em>that</em></strong> be? They are both NSDates, right? Actually, I have the same problem with bindings to everything; none of my UI objects will work with my model.</p>
  
  <p>The only thing I can figure is that there is something going wrong in the connection between the File's Owner and the NSArrayController.</p>
  
  <p>I haven't written any code at this point, because I'm of the understanding I shouldn't have to just to link UI fields and core data. Is it different because I am using a document-based application? (I can't get it to work in a single window app, either.)</p>
  
  <p>An answer of "don't use Core Data" isn't going to be productive; I know I can just fall back on a regular data object. I would like to figure this out in the context of Core Data if possible.</p>
  
  <p>TIA!</p>
  
  <p>(Update: this question seems to be vexing a lot of people. I have consulted the Zarra book on Core Data, the Hillegas book on Cocoa Programming, and two O'Reilly books. They all seem to be based on Xcode 3.)</p>