on 4/21/08 2:06 AM, [EMAIL PROTECTED] purportedly said: > I am trying to figure out how to calculate a running total using core > data. I have created an entity called Transactions that have the > following properties. > > Transactions > amount > balance > > <snip> > > This routine only copies the amount to the balance property. I am > thinking that I have to Query all of the previous transactions and > calculate their totals. I know how to create a NSFetchRequest on a > transaction object but I am unsure on how to create the NSPredicate > object to extract all the transactions that were created prior to the > current transaction. Thanks for any help you can provide.
First issue I see is how you can know what transaction objects "occur" prior to any given object. I don't think you can rely on objects being retrieved in any specific order that your data model doesn't enforce. Next, AFAIK, there is no way to do what you want purely from an entity's perspective--i.e. through a predicate or any instance method of the entity class--unless you can rely that -awakeFromFetch is called in a predictable order (which I can't answer), and you are willing to recalculate the entire data set every time any change is made. Otherwise, an outside "controller" object, perhaps who can watch for certain changes or gets called at certain strategic times, will perform re/calculations when needed. HTH, Keary Suska Esoteritech, Inc. "Demystifying technology for your home or business" _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [EMAIL PROTECTED]
