Right cocoa collections

//worst
NSArray *sessionsFromServer = ...;
NSManagedObjectContext *context = ...;

for (WWDCSession *aSession in sessionsFromServer) {
    NSFetchRequest *req = [NSFetchRequest fetchRequestWithEntityName:@"WWDCSession"];
    req.predicate = [NSPredicate predicateWithFormat:@"sessionID == %@", aSession.sessionID];
    NSArray *results = [context executeFetchRequest:req error:nil];

    WWDCSession *existSesion = [results firstObject];
    if (!existSesion) {
        //Insert a New One
    }else {
        // Do something with the existSession
    }
}

//better
NSArray *sessionsFromServer = ...;
NSManagedObjectContext *context = ...;

NSArray *sessionIDs = [sessionsFromServer valueForKey:@"SessionID"];
NSFetchRequest *req = [NSFetchRequest fetchRequestWithEntityName:@"WWDCSession"];
req.predicate = [NSPredicate predicateWithFormat:@"sessionID in %@", sessionIDs];
NSArray *results = [context executeFetchRequest:req error:nil];

for (WWDCSession *aSession in sessionsFromServer) {
    NSInteger existingSessionIndex = [results indexOfObject:aSession];
    if (existingSessionIndex == NSNotFound) {
        //Insert a New One
    }else {
        // Do something with the existSession
    }
}

//right
NSArray *sessionsFromServer = ...;
NSManagedObjectContext *context = ...;

NSArray *sessionIDs = [sessionsFromServer valueForKey:@"SessionID"];
NSFetchRequest *req = [NSFetchRequest fetchRequestWithEntityName:@"WWDCSession"];
req.predicate = [NSPredicate predicateWithFormat:@"sessionID in %@", sessionIDs];
NSArray *results = [context executeFetchRequest:req error:nil];
NSDictionary *mapDic = [NSDictionary dictionaryWithObjects:results forKeys:[results valueForkey:@"sessionID"]];

for (WWDCSession *aSession in sessionsFromServer) {
    WWDCSession *existingSession = mapDic[aSession.sessionID];
    if (!existingSession) {
        //Insert a New One
    }else {
        // Do something with the existSession
    }
}