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Triggered NSObjectController
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Triggered NSObjectController


  • Subject: Triggered NSObjectController
  • From: Vincent Coetzee <email@hidden>
  • Date: Tue, 31 Jan 2006 21:43:55 +0200

Dear List,

I have been using Bindings and CoreData for a while now, and the similarity between Bindings and something that Visualworks Smalltalk had called AspectAdaptors is striking. The one place though, where I find something missing from bindings is when one is attempting to edit a pre-existing object in CoreData, and then before any editing is committed to the store, one has a requirement to update some other object also in CoreData. In this case it becomes difficult to separate out the changes made by the editing from some other changes that were perhaps made against the current ManagedObjectContext.

VisualWorks had a lovely solution to this problem, called a TriggeredAspectAdaptor, where in effect the changes made via bindings, were held isolated from the currently active context until a boolean value went true, at which point, the changes held by the triggered binding were propagated to the current context. This allowed the current context to be committed or rolled back without affecting the editing. I also find it complicated to have to add a ManagedObject to the store just so that I can edit and then if the user clicks "Cancel" have to explicitly delete it, rather than just throwing the reference away. Yes this is simple in the case where a one dimensional object is being edited, but when the new object contains a multitude of other objects, it becomes messy.

Does anyone have an idea of how one could possibly implement something like this, or does such functionality already exist. I have tried to implement a subclass of NSObjectController that handles triggering, but unfortunately it gets complicated when one used keypaths in the bindings, since the ObjectController does not get asked for the complete keypath, but only a portion of it, which means one has to wrap each successive layer in something to manage the triggering.

Comments would be interesting ?

Vincent
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