Core Data : Batch Faulting while take advantage of cache
Core Data : Batch Faulting while take advantage of cache
- Subject: Core Data : Batch Faulting while take advantage of cache
- From: Bob Cromwell <email@hidden>
- Date: Wed, 14 Nov 2012 11:44:39 +0800
Hi there,
In "Core Data Programming Guide" Apple recommend a way to batch fire fault a collection of objects, It should be implemented as below:
NSArray * arrayOfFaults = [NSArray arrayWithObjects:object1,object2,nil];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"self IN %@", arrayOfFaults];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Foo"];
[fetchRequest setPredicate:predicate];
[fetchRequest setReturnsObjectsAsFaults:NO];
[managedObjectContext executeFetchRequest:fetchRequest error:NULL];
However using "Core Data" Instrument on iOS 6 simulator, I found this fetch almost as same time as other fetch. In other words, it goes to disk and did not use the cache. It's unreasonable . Since it's an " IN " clause , Core Data could use the objectID to find object in cache. There are no need to go to the disk if all of them could be found in cache.
I am pretty sure these objects in arrayOfFaults are in cache. If I replace above code with this one, not cache miss are reported:
for (NSManagedObject *object in arrayOfFaults){
[object willAccessValueForKey:nil];
}
So my question is : are there any way to batch fault objects while take advantage of the cache ?
Bob Cromwell
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