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I’ve been trying to get this work for several days now and it becomes an headache for me…

I’ve created a NSArrayController that is responsible for a set of NSManagedObjects. One of the related entity property is a ‘category’ relationship. Another CategoryArrayController is then associated to that entity.

What I want to do is to manage Categories through a NSComboBox box. I’ve set bindings to :

content : CategoryArrayController.arrangedObjects

contentValues : CategoryArrayController.arrangedObjects.category

value : TransactionArrayController.selection.category

That works fine for programmatically added category value, that is I can select them through the NSComboBox. However, I cannot add a new category in the user interface. When I enter it, I get a message :

2005-11-28 11:44:10.198 test[426] ** -[NSCFString _isKindOfEntity:] selector not recognized [self = 0x3f7b90]*

Does anyone have a idea for that ?

Well, I assume that “category” is a to-one relationship to a “category” entity. contentValues (note the pluralization) should be pointing to a set (a to-many relationship) like “categories” … further, it should be pointed to a string value (because contentValues is alist of the strings that will be displayed to the user) … So it should be arrangedObjects.categories.categoryTitle or something similar.

… oops - let me amend my statement after looking more closely. Your CategoryArrayController controls your “categories” … so, assuming your category entity has a “categoryTitle” or similar string property, contentValues should be bound to arrangedObjects.categoryTitle. Sorry for any confusion caused by my quick answer.

I finally managed to do it. Here is the final mail I posted to the cocoa mailing list

So I’ve got the following model (credits to Wain ;) :

< Transaction > < category > «————> < Category > < category >

The NSCombobox ‘ bindings should be set to

    content : CategoryArrayController.arrangedObjects
    contentValues : CategoryArrayController.arrangedObjects.category
    value : TransactionArrayController.selection.category.category

Indeed, value expects a NSString, to be printed in the text area of the NSCombobox.

Now, Coredata cannot automatically update the ‘category’ Relationship in the Transaction Entity, as the value in not a NSManagedObject.

So we must intercept the NSCombox Selection change, and code it ourselves. I did it with comboBoxSelectionDidChange: delegate method :

Ok, what about adding new category ? I had a little problem, because :

I had to do something “very early”, so I use the NSComboBox contr:isValidObject: delegate method (from NSControl).