On 2009 Jun 21, at 09:55, Quincey Morris wrote:
First, you *seem* to be suggesting that uniquing is a process of
winnowing away unwanted duplicate objects, but I'm pretty sure that
Core Data doesn't create duplicate objects. Rather, it seems likely
that it uses the object UID to find out if a needed object exists
before ever creating it.
Oh, I agree with you on that. I thought it was rather strange to read
an "-ing" suffix on "uniqueing", as though it was something that could
"happen".
Second, "Fetch all Bars" isn't a scenario where spurious duplicate
Bars could be created.
It looks like you're correct. I just tried to reproduce this in the
Core Data Utility but found that it worked as expected -- setting the
same Bar to two different Foos does not create an additional Bar [1].
Also, you could examine the UIDs of foo1, foo2 and bar before and
after the save, as well as after the fetch. Unless you can see 2
different objects with the same UID, then it would seem that the
unwanted Bar was actually created as a result of your code somewhere.
Good idea. If I don't reply back to this thread it means I found
something stupid in my code.
Thanks, Quincey.
Jerry
[1]
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
// Note: This function returns a retained, not autoreleased, instance.
NSManagedObjectModel *getStaticManagedObjectModel() {
static NSManagedObjectModel *mom = nil;
if (mom != nil) {
return mom;
}
mom = [[NSManagedObjectModel alloc] init];
NSEntityDescription *fooEntity = [[NSEntityDescription alloc]
init];
[fooEntity setName:@"Foo"];
[fooEntity setManagedObjectClassName:@"Foo"];
NSEntityDescription *barEntity = [[NSEntityDescription alloc]
init];
[barEntity setName:@"Bar"];
[barEntity setManagedObjectClassName:@"Bar"];
// Create a to-one relationship
NSRelationshipDescription *fooToBar = [[NSRelationshipDescription
alloc] init] ;
[fooToBar setMaxCount:1] ;
[fooToBar setName:@"bar"] ;
// Create a to-many relationship
NSRelationshipDescription *barToFoo = [[NSRelationshipDescription
alloc] init] ;
[barToFoo setMaxCount:NSIntegerMax] ;
[barToFoo setName:@"foos"] ;
// Wire up the relationships
[fooToBar setDestinationEntity:barEntity] ;
[barToFoo setDestinationEntity:fooEntity] ;
[fooToBar setInverseRelationship:barToFoo] ;
[barToFoo setInverseRelationship:fooToBar] ;
// Set relationships in entities
[fooEntity setProperties:[NSArray arrayWithObject:fooToBar]] ;
[barEntity setProperties:[NSArray arrayWithObject:barToFoo]] ;
[fooToBar release] ;
[barToFoo release] ;
// Set entities in mom
[mom setEntities:[NSArray arrayWithObjects:
fooEntity,
barEntity,
nil]];
[fooEntity release] ;
[barEntity release] ;
return mom;
}
// Note: This function returns a retained, not autoreleased, instance.
NSManagedObjectContext *getStaticManagedObjectContext() {
static NSManagedObjectContext *moc = nil;
if (moc != nil) {
return moc;
}
moc = [[NSManagedObjectContext alloc] init];
NSPersistentStoreCoordinator *coordinator =
[[NSPersistentStoreCoordinator alloc]
initWithManagedObjectModel: getStaticManagedObjectModel()];
[moc setPersistentStoreCoordinator: coordinator];
[coordinator release] ;
NSError *error;
NSPersistentStore *newStore ;
newStore = [coordinator
addPersistentStoreWithType:NSInMemoryStoreType
configuration:nil
URL:nil
options:nil
error:&error];
if (newStore == nil) {
NSLog(@"Store Configuration Failure\n%@",
([error localizedDescription] != nil) ?
[error localizedDescription] : @"Unknown Error");
}
return moc;
}
int main (int argc, const char * argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
// Create Core Data stack
NSManagedObjectModel *mom = getStaticManagedObjectModel() ;
NSManagedObjectContext *moc = getStaticManagedObjectContext() ;
// Create two Foos and one Bar
NSManagedObject* foo1 = [NSEntityDescription
insertNewObjectForEntityForName:@"Foo"
inManagedObjectContext:moc] ;
NSManagedObject* foo2 = [NSEntityDescription
insertNewObjectForEntityForName:@"Foo"
inManagedObjectContext:moc] ;
NSManagedObject* bar = [NSEntityDescription
insertNewObjectForEntityForName:@"Bar"
inManagedObjectContext:moc] ;
// Set the single bar to be the Bar of each Foo
[foo1 setValue:bar
forKey:@"bar"] ;
[foo2 setValue:bar
forKey:@"bar"] ;
NSFetchRequest* fetchRequest ;
NSArray* fetches ;
// Fetch and log all the Foos.
fetchRequest= [[NSFetchRequest alloc] init];
[fetchRequest setEntity:[NSEntityDescription entityForName:@"Foo"
inManagedObjectContext:moc]];
fetches = [moc executeFetchRequest:fetchRequest
error:NULL] ;
NSLog(@"Fetched %d Foos: %@", [fetches count], fetches) ;
[fetchRequest release] ;
// Fetch and log all the Bars.
fetchRequest= [[NSFetchRequest alloc] init];
[fetchRequest setEntity:[NSEntityDescription entityForName:@"Bar"
inManagedObjectContext:moc]];
fetches = [moc executeFetchRequest:fetchRequest
error:NULL] ;
NSLog(@"Fetched %d Bars: %@", [fetches count], fetches) ;
[fetchRequest release] ;
[moc release] ;
[mom release] ;
[pool release] ;
return 0;
}
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