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Problem adding an entity to a to-many relationship

I am trying to get my head round Core Data and Bindings. I have created a simple core data model consisting of two entities called Course and Student. There is a to-many relationship from Course to Student. I have created a view with one table for Courses and another for students. There is a button for adding courses. That works fine. I also have a button which when clicked gets a CSV file containing student details. For each student in the file I want to create a new entity and have the following code in my NSPersistentDocument subclass:

NSManagedObjectContext *context = [self managedObjectContext];
Student *student = [NSEntityDescription insertNewObjectForEntityForName:@"Student" inManagedObjectContext:context];

This seems to work OK. I then update the fields with data from the CSV file.

The problem comes when I try to add the student to its owning course.

I get the course from the array controller using:

	Course *course = [[coursesController selectedObjects] objectAtIndex:0];

This seems to return the correct entity.

Then I then add the student using the predefined accessor:

	[course addStudentsObject:student];

This fails in the call [NSBinder _invokeSelector:withAguments:onKeyPath:ofObject:mode:raisesForNotApplicableKeys :]

I'm using the latest version of XCode and have got garbage collection switched on.

I hope someone can sort me out.

Cheers
Keith
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