iphone - 优化此核心数据请求

Question

我在Core Data中有一个名为MusicInterest的实体。我必须一次添加5000个左右，而我当前的过程是查询以查看MusicInterest是否已经存在，如果不创建一个新的。

看来这需要五千次前往商店，以查看每个标题是否存在。当然，也有插入行程，但是5000个查询使我很慢。

每个FacebookFriend都会有多种音乐兴趣，我使用一系列字符串标题枚举每个音乐 friend ，并调用以下代码。

任何想法如何优化呢？

+ (MusicInterest*) musicInterestForFacebookFriend:(FacebookFriend*)facebookFriend WithTitle:(NSString*)musicTitle UsingManagedObjectContext:(NSManagedObjectContext*)moc
{
    // query to see if there
    NSArray *matches = [self queryForMusicTitle:musicTitle moc:moc];

    if (([matches count] >= 1)) {
        // NSLog(@"Music already in database");
        MusicInterest *existingMusic = [matches lastObject];
        [existingMusic addLikedByObject:facebookFriend];
        return [matches lastObject];
    } else {
        // create new Music Interest
        MusicInterest *newMusic = [NSEntityDescription insertNewObjectForEntityForName:@"MusicInterest" inManagedObjectContext:moc];
        newMusic.title = musicTitle;
        [newMusic addLikedByObject:facebookFriend];
        return newMusic;
    }
}

+ (NSArray *)queryForMusicTitle:(NSString *)MusicTitle moc:(NSManagedObjectContext *)moc
{
    // query to see if there
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"MusicInterest"];
    request.predicate = [NSPredicate predicateWithFormat:@"title == %@", [NSString stringWithFormat:@"%@", MusicTitle]];

    NSError *error = nil;
    NSArray *matches = [moc executeFetchRequest:request error:&error];
    if (error) {
        NSLog(@"Error querying title in Music interest. Error = %@", error);
    }
    return matches;
}

更新:

我采用了Core Data编程指南中建议的设计，并将我的时间从12秒减少到4秒(仍然需要在其他方面进行一些优化:)

该指南仅包含示例代码的一半-我想我将分享完整的实现:

musicArray = [[music componentsSeparatedByString:@", "] sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
                if (obj1 > obj2)
                    return NSOrderedDescending;
                else if (obj1 < obj2)
                    return NSOrderedAscending;
                return NSOrderedSame;
            }];

            if (musicArray) {

                NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"MusicInterest"];
                [fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"title IN %@", musicArray]];
                [fetchRequest setSortDescriptors:
                 @[[[NSSortDescriptor alloc] initWithKey: @"title" ascending:YES]]];

                NSError *fetchError = nil;
                NSArray *musicInterestMatchingTitles = [backgroundContext executeFetchRequest:fetchRequest error:&fetchError];

                if ([musicArray count] > 0) {
                    // walk musicArray and musicInterestsMatchingTitles in parallel
                    for (int i = 0; i < [musicArray count]; i++) {
                        NSString *title = musicArray[i];
                        if (i < [musicInterestMatchingTitles count]) {
                            MusicInterest *comparingMusicInterest = musicInterestMatchingTitles[i];
                            // compare each title
                            if (![title isEqualToString:comparingMusicInterest.title]) {
                                // if it doesn't exist as a ManagedObject (a MusicInterest), create one
                                MusicInterest *musicInterest = [MusicInterest createNewMusicInterestUsingManagedObjectContext:backgroundContext];
                                musicInterest.title = title;
                                [musicInterest addLikedByObject:friend];
                            } else {
                                // otherwise, just establish the relationship
                                [comparingMusicInterest addLikedByObject:friend];
                            }
                        } else {
                            // if there are no existing matching managedObjects, create one
                            MusicInterest *musicInterest = [MusicInterest createNewMusicInterestUsingManagedObjectContext:backgroundContext];
                            musicInterest.title = title;
                            [musicInterest addLikedByObject:friend];
                        }
                    }
                }
            }

        }];
        [self saveBackgroundContext:backgroundContext];

Answer 1

“核心数据编程指南”中的Implementing Find-or-Create Efficiently描述了一种可能在此处有用的模式。基本思想是:

通过一些也要存储在其中的唯一ID对要插入/更新的项目列表进行排序
数据库。

执行一个获取请求，该请求从数据库中获取列表中具有ID(按相同ID排序)的所有对象。

现在并行遍历您的列表和获取的项目数组，以查找必须插入的项目以及已经存在的项目并可以对其进行更新。