Hello Al!
Summary: It looks like [NSManagedObjectContext
executeFetchRequest:error:] starts to evaluate a predicate ([NSPredicate
evaluateWithObject:]) with objects that was not requested and was not fetched
from a database.
Our application makes prefetching of CoreData
entities with relationships like
NSFetchRequest* requestRelatedTags = [[[ NSFetchRequest
alloc] init] autorelease];
[requestRelatedTags setEntity : [ NSEntityDescription
entityForName : kFSIValueElementA inManagedObjectContext
: [ md managedObjectContext ]] ]; [requestRelatedTags
setFetchLimit: 1000000 ]; NSPredicate * predicate = [
NSPredicate predicateWithFormat: @"(self IN %@)",[items
valueForKey: @"objectID"]]; [requestRelatedTags
setPredicate:predicate];
[requestRelatedTags setRelationshipKeyPathsForPrefetching : [
NSArray arrayWithObjects : @"tags" , nil
]]; [requestRelatedTags setReturnsObjectsAsFaults:
true]; items0_ = [[md managedObjectC
ontext ] executeFetchRequest : requestRelatedTags error :
nil ];
where "items" is an array of 100 NSManagedObjects, "tags" is
to-many relationship of the kFSIValueElementA entity with inverse to-one
relationship.
At start this code works quickly and takes fixed amount of time
(0.03-0.04 sec) every time. But at some point it starts to work very slowly
taking more and more time. Instruments shows that it fetches 100 objects every
time from a database. But Shark shows that it uses [NSPredicate
evaluateWithObject:] more and more times. To be precise, it invokes
[NSPredicate evaluateWithObject:] 100 times more every time. [NSPredicate
evaluateWithObject:] is invoked every time from [NSManagedObjectContext
executeFetchRequest: error:].
We added logging to [NSPredicate evaluateWithObject:] and we see
that it is evaluated on objets that was not requested by the fetch request and
was not fetched from the SQLite database. Thus this is a bug in
[NSManagedObjectContext executeFetchRequest:error:]. It should not filter
objects that was not.
Does anybody have any ideas how to solve this problem?
Best Regards, Oleksiy Gorelov
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