Re: Core Data: updating a key dependent on a to-many relationship?
Re: Core Data: updating a key dependent on a to-many relationship?
- Subject: Re: Core Data: updating a key dependent on a to-many relationship?
- From: Nathan Tyler <email@hidden>
- Date: Thu, 2 Feb 2006 17:37:35 -0800
Thanks for the links, that got me started. I am writing a simple
invoice setup and need the invoice's subtotal to update when one of
the line items changes. I have a parent object Invoice with a to-many
relationship LineItems.
I have a version of the code that works now after having some initial
issues. I now create a new LineItem in my controller, use
addObserver:, and then use the addLineItemObject: command in Invoice.
awakeFromInsert: I know will not work because that will only be called
when it's first put into the object graph (and you can't seem to
access the inverse relationship to Invoice at that point anyway)
Is there a way to add the observer inside the LineItem object as it's
initialized (at the same time it sets the inverse relationship to
Invoice, whenever it does that)? I'm not sure how to implement this.
Any help would be appreciated.
Thanks,
Nathan
On 1/30/06, mmalcolm crawford <email@hidden> wrote:
>
> On Jan 29, 2006, at 11:14 AM, Nathan Tyler wrote:
>
> > I am developing a Core Data application that has an entity with a
> > to-many relationship with another entity. I need to notify the
> > parent/single object when its corresponding "many" entities are
> > edited/added/removed in order to update a total, average, etc. In
> > this case the triggerChangeNotificationsForDependentKey will not work.
> > I have found a corresponding section in Apple's Core Data FAQ:
> > http://developer.apple.com/documentation/Cocoa/Conceptual/CoreData/
> > Articles/cdFAQ.html#//apple_ref/doc/uid/TP40001802-
> > DontLinkElementID_13
> > This seems to be the exact example of what I need. However, as it
> > is one of my first endeavors in this area, I need some basic help on:
> > "You must add and remove the parent as an observer as child objects
> > are added to and removed from the relationship."
> > I'm not sure how to do this.
>
> See <http://developer.apple.com/documentation/Cocoa/Conceptual/
> KeyValueObserving/Concepts/KVOBasics.html#//apple_ref/doc/uid/
> 20002252> for a discussion of registering as an observer using KVO.
>
> See <http://homepage.mac.com/mmalc/CocoaExamples/controllers.html>
> [Graphics Bindings] for an example of observing an array using KVO
> and responding to changes.
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