Re: Predicate Builder & Fetched Properties
Re: Predicate Builder & Fetched Properties
- Subject: Re: Predicate Builder & Fetched Properties
- From: mmalcolm crawford <email@hidden>
- Date: Tue, 5 Jul 2005 14:48:43 -0700
On Jul 5, 2005, at 1:04 PM, Charilaos Skiadas wrote:
On Jul 5, 2005, at 2:49 PM, mmalcolm crawford wrote:
<<http://developer.apple.com/documentation/Cocoa/Reference/
CoreData_ObjC/Classes/NSFetchedPropertyDesc.html>
"The effect of a fetched property is similar to executing the
fetch request yourself and placing the results in a transient
attribute, although with the framework managing the details. In
particular, a fetched property is not fetched until it is
requested, and the results are then cached until the object is
turned into a fault. You use -refreshObject:mergeChanges:
(NSManagedObjectContext) to manually refresh the properties—this
causes the fetch request associated with this property to be
executed again when the object fault is next fired."
I've read this, but maybe I haven't fully understood it. So, if I
understand correctly, there are two options:
1) I can write code for the fetch request myself.
Do you mean, you can simply create and execute a fetch request
periodically? Of you can put a fetch request in an accessor method?
2) I can have any controller that changes things that affect the
given property call a refreshObject:mergeChanges: each time it
changes things.
It's this second option that I expected one could do through KVO,
without having to write any code. So I guess the question is: can
one register the fetched property to observe changes in some keys,
Can you register it using
setKeys:triggerChangeNotificationsForDependentKey:? -- no.
You can add your own observation code...
But most importantly, why would one need to write code about this
at all? I guess maybe I've gotten too spoiled with CoreData, but I
would expect this to be exactly the sort of thing that CD would
allow you to do without any code.
Please file an enhancement request.
On a related note, maybe I've missed it, but I haven't been able to
find a lot of examples on the web about how to use fetched
properties and fetch requests, so if someone can point me to some
links, I would appreciate it.
What additional examples or explanation would you like? I think
these cover all the uses of fetch requests:
<http://developer.apple.com/documentation/Cocoa/Reference/
CoreData_ObjC/Classes/NSManagedObjectContext.html#//apple_ref/doc/uid/
TP30001182-BAJDFCJJ>
<http://developer.apple.com/documentation/Cocoa/Conceptual/
CoreDataUtilityTutorial/07_Fetch/chapter_8_section_2.html#//apple_ref/
doc/uid/TP40001800-CH230-DontLinkElementID_32>
<http://developer.apple.com/documentation/Cocoa/Conceptual/
NSPersistentDocumentTutorial/04_Department/chapter_5_section_3.html#//
apple_ref/doc/uid/TP40001799-CH223-DontLinkElementID_25>
See also, <http://developer.apple.com/documentation/Cocoa/Conceptual/
Predicates/Articles/pCreating.html>.)
There are also several source examples in Core Recipes <http://
developer.apple.com/samplecode/CoreRecipes/CoreRecipes.html>.
mmalc
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