Re: KVO / Core Data question
Re: KVO / Core Data question
- Subject: Re: KVO / Core Data question
- From: Diederik Hoogenboom <email@hidden>
- Date: Wed, 14 Dec 2005 21:00:02 +0100
Paul,
Maybe you can use a fetched property for this. I seem to remember
that you can also use "sum()" as an expression.
Regards,
Diederik
On 14-dec-2005, at 17:49, Paul L. Gribble wrote:
I have an entity "Trip" that has a to-many relationship to another
entity,
"Transaction" via a relationship called "transaction".
The Trip entity has a key called "balance" whose value I want to
depend on
the sum of all of the "amount" keys of each transaction.
I understand from reading Apple's Core Data FAQ (pg. 108-109) that
it's not
possible to do this using
setKeys:triggerChangeNotificationsForDependentKey,
where the key would be a key-path (e.g. email@hiddent).
The FAQ suggests two solutions - one, use KVO to register the
parent as an
observer of the relevant attribute of all the children; and one
must then
add and remove the parent as an observer, each time child objects
are added
to or removed from the relationship. This seems not very efficient
compared
to the second suggestion:
register the parent with the application's notification center as an
observer of its managed object context. This seems like less coding
to me,
but there are no examples. Can anyone provide, or point me to, a code
snippet showing how one would do this?
Thanks,
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