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POModeling user-orderable lists with Core Data / Bindings
 

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    <p>I'm working through a learning project around Core Data on OS X. I have an entity (Foo) in the data store, and in the UI, I use an NSArrayController with bindings to put some (name) field of the Foo objects into an NSTableView, where the user can add/delete/rename (and potentially reorder) the items.</p> <p>As you know, Core Data storage is unordered. However, I'd like to give it order from the user standpoint. E.g. adding a new row to the table view fixes that new Foo to the end of the list, etc. If the table allows reordering, that order is maintained.</p> <p>I assume that I should accomplish this by adding some hidden (ie the user never encounters it) "ordinal" field to the Foo entity, which is fine. I'm trying to figure out:</p> <ol> <li>Where is the right place to set this "ordinal" field for new items? Right now, a button is invoking the <code>add:</code> action on the array controller and bindings handles all the rest magically. (I'll need access to the count of items to set it correctly.)</li> <li>Where is the right place to fixup the whole result set's ordinals on delete or reorder?</li> <li>Assuming all objects in the store have a reasonable ordinal attribute, what must I do to the UI connections to get the table view to display the results sorted by that ordinal? Is this something I can do purely with bindings? Do I need to subclass... something? </li> </ol> <p>It feels like this is a common enough scenario that people here might have a ready answer. I'm new to Core Data and bindings-- trying to grope my way around. Don't need code; pointers in the right direction would be great. Thanks.</p>
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