I think the single most useful thing I’ve figured out recently in programming for MacOSX and the iPhone is this little snippet right here.

- (void) updateListForEntityNamed:(NSString*) entityName andSearchString:(NSString*) queryString
{
[...]
 
	MyDocument* current = [[NSDocumentController sharedDocumentController] currentDocument];
	if(current && current != self)
	{
		NSLog(@"CurrentDocument:%@ != self:%@", current, self);
		[current updateListForEntityNamed: entityName andSearchString: queryString];
		return;
	}
[...]
}

What this does is intercept incoming messages that are supposed to go to the current window, and redirect them to that instance. I’ve run into issues in Leopard (MacOSX 10.5) where this is an issue. To some extent, this is probably a misconfiguration in interface builder somewhere, but it also an issue when using CoreData, because the ManagedObjectContexts are particular to instances of NSManagedDocument, and there are issues that arise if you end up using the wrong context.

I am slowly becoming a great fan of CoreData, it’s a great persistence/object-graph-management layer. More on this later.