Adding unique objects to Core Data

Question

I'm working on an iPhone app that gets a number of objects from a database. I'd like to store these using Core Data, but I'm having problems with my relationships.

A Detail contains any number of POIs (points of interest). When I fetch a set of POI's from the server, they contain a detail ID. In order to associate the POI with the Detail (by ID), my process is as follows: Query the ManagedObjectContext for the detailID. If that detail exists, add the poi to it. If it doesn't, create the detail (it has other properties that will be populated lazily).

The problem with this is performance. Performing constant queries to Core Data is slow, to the point where adding a list of 150 POI's takes a minute thanks to the multiple relationships involved.

In my old model, before Core Data (various NSDictionary cache objects) this process was super fast (look up a key in a dictionary, then create it if it doesn't exist)

I have more relationships than just this one, but pretty much every one has to do this check (some are many to many, and they have a real problem).

Does anyone have any suggestions for how I can help this? I could perform fewer queries (by searching for a number of different ID's), but I'm not sure how much this will help.

Some code:

        POI *poi = [NSEntityDescription
                insertNewObjectForEntityForName:@"POI"
                inManagedObjectContext:[(AppDelegate*)[UIApplication sharedApplication].delegate managedObjectContext]];

    poi.POIid = [attributeDict objectForKey:kAttributeID];
    poi.detailId = [attributeDict objectForKey:kAttributeDetailID];
    Detail *detail = [self findDetailForID:poi.POIid];
    if(detail == nil)
    {
        detail = [NSEntityDescription
                    insertNewObjectForEntityForName:@"Detail"
                    inManagedObjectContext:[(AppDelegate*)[UIApplication sharedApplication].delegate managedObjectContext]];
        detail.title = poi.POIid;
        detail.subtitle = @"";
        detail.detailType = [attributeDict objectForKey:kAttributeType];
    }





-(Detail*)findDetailForID:(NSString*)detailID {
NSManagedObjectContext *moc = [[UIApplication sharedApplication].delegate managedObjectContext];
NSEntityDescription *entityDescription = [NSEntityDescription
                                          entityForName:@"Detail" inManagedObjectContext:moc];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:entityDescription];

NSPredicate *predicate = [NSPredicate predicateWithFormat:
                          @"detailid == %@", detailID];
[request setPredicate:predicate];
NSLog(@"%@", [predicate description]);

NSError *error;
NSArray *array = [moc executeFetchRequest:request error:&error];
if (array == nil || [array count] != 1)
{
        // Deal with error...
    return nil;
}
return [array objectAtIndex:0];
}

Answer 1

Check out the section titled "Batch Faulting" on the page titled "Core Data Performance" in Xcode's Core Data Programming Guide that Norman linked to in his answer.

Only fetching those managedObjects whose ids are IN a collection (NSSet, NSArray, NSDictionary) of ids of the objects returned by the server may be even more efficient.

NSSet *oids = [[NSSet alloc] initWithObjects:@"oid1", @"oid2", ..., nil];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"oid IN %@", oids];
[oids release];

UPDATE: I worked this tip into a solution for the acani usersView. Basically, after downloading a JSON response of users, the iPhone uses the popular open source JSON framework to parse the response into an NSArray of NSDictionary objects, each representing a user. Then, it makes an NSArray of their uids and does a batch fetch on Core Data to see if any of them already exist on the iPhone. If not, it inserts it. If so, it updates the ones that do exist only if their updated attribute is older than that of the one from the server.