核心数据优化

Question

我在 NSDictionary 中有大量用户，其结构如下：

        97 =             {
            birthday = "";
            gender = Unspecified;
            image =                 {
                status = Prepared;
                type = Image;
            };
            "name_display" = "Facebook User";
            "name_first" = Facebook;
            "name_last" = User;
            type = Contact;
            "user_id" = 97;
        };
        98 =             {
            birthday = "";
            gender = Unspecified;
            image =                 {
                status = Prepared;
                type = Image;
            };
            "name_display" = "Facebook User";
            "name_first" = Facebook;
            "name_last" = User;
            type = Contact;
            "user_id" = 98
         }

我想将此数据输入到 Core Data 中。首先我必须检查用户是否已经存在于核心数据中。如果是这样，请更新该用户。否则创建一个新用户。我这样做的方式有效，但速度非常慢。这是我的代码：

NSDictionary *users = [responseData objectForKey:@"users"];
if (users) {
    for (id userKey in [users allKeys]) {
        NSDictionary *contactDictionary = [users objectForKey:userKey];
        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"userID == %@", userKey];
        NSUInteger count = [CoreDataHelper countForEntity:@"Contact" withPredicate:predicate andContext:[FSAppDelegate managedObjectContext]];
        if (count > 0) {
            NSMutableArray *existingContactArray = [CoreDataHelper searchObjectsForEntity:@"Contact" withPredicate:predicate andSortKey:nil andSortAscending:NO andContext:[FSAppDelegate managedObjectContext]];
            Contact *existingContact = [existingContactArray objectAtIndex:0];
            [CoreDataHelper updateContactWithDictionary:contactDictionary forContactObject:existingContact];
        }
        else {
            Contact *newContact = (Contact*)[NSEntityDescription insertNewObjectForEntityForName:@"Contact" inManagedObjectContext:[FSAppDelegate managedObjectContext]];
            [CoreDataHelper updateContactWithDictionary:contactDictionary forContactObject:newContact];
        }
    }

    NSError *error;
    if (![[FSAppDelegate managedObjectContext] save:&error]) {
        // Handle the error.
        NSLog(@"error saving to db - fsrequest class.");
    }
}

这是我更新联系人的方法

+(BOOL)updateContactWithDictionary:(NSDictionary*)changedContact forContactObject:(Contact*)contact {
NSString *bday = [changedContact valueForKey:@"birthday"];
NSString *gender = [changedContact valueForKey:@"gender"];
NSString *nameDisplay = [changedContact valueForKey:@"name_display"];
NSString *nameFirst = [changedContact valueForKey:@"name_first"];
NSString *nameLast = [changedContact valueForKey:@"name_last"];
NSString *type = [changedContact valueForKey:@"type"];
NSString *userID = [NSString stringWithFormat:@"%@",[changedContact valueForKey:@"user_id"]];
NSString *imageStatus = [[changedContact objectForKey:@"image"]objectForKey:@"status"];
NSString *imageType = [[changedContact objectForKey:@"image"]objectForKey:@"type"];
NSString *imageURL = [[changedContact objectForKey:@"image"]objectForKey:@"url"];
NSString *imageThumb = [[changedContact objectForKey:@"image"]objectForKey:@"url_thumb"];
NSString *locationName = [[changedContact objectForKey:@"location"]objectForKey:@"name"];

[contact setBirthday:bday];
[contact setGender:gender];
[contact setNameDisplay:nameDisplay];
[contact setNameFirst:nameFirst];
[contact setNameLast:nameLast];
[contact setType:type];
[contact setUserID:userID];
[contact setImageStatus:imageStatus];
[contact setImageType:imageType];
if (imageURL && !((NSNull *)imageURL == [NSNull null])) {
    [contact setImageURL:imageURL];
}
if (imageThumb && !((NSNull *)imageThumb == [NSNull null])) {
    [contact setImageThumbURL:imageThumb];
}
if (locationName && !((NSNull *)locationName == [NSNull null])) {
    [contact setLocationName:locationName];
}
return YES;
}

谁能给我一个例子，说明我将如何以更快的方式做到这一点？有些人提到了一些想法，但我需要看到它才能理解。谢谢！

Answer 1

您需要了解获取请求的成本很高（它需要运行 SQL 并执行 I/O）。我不确定你的CoreDataHelper 来自哪里，但它会做某种昂贵的NSFetchRequest。您可以构造一个NSFetchRequest，它会告诉您哪些对象已经存在。这会将成本从 O(N) 降低到 O(1)。

[request setPredicate:[NSPredicate predicateWithFormat:@"userID IN %@", allKeys]];

并且，如上所述，将保存移出循环。 但是如果您要更新添加 许多 个对象，您可能需要不时保存。

Answer 2

首先，我将 save: 移到循环之外。替换：

 // save core data
        NSError *error;
        if (![[FSAppDelegate managedObjectContext] save:&error]) {
            // Handle the error.
            NSLog(@"error saving to db - fsrequest class.");
        }
    }
}

与

    }
    // save core data
    NSError *error;
    if (![[FSAppDelegate managedObjectContext] save:&error]) {
    // Handle the error.
    NSLog(@"error saving to db - fsrequest class.");
  }
}

另外，你有一些在 Core Data 模型中定义的 imageURL、imageThumb 和 locationName 的默认值吗？如果不是，为什么要检查空值（两次）？

奖励：

消除 countForEntity:withPredicate:andContext: 调用可能是个好主意，如下所示：

NSMutableArray *existingContactArray = [CoreDataHelper searchObjectsForEntity:@"Contact" withPredicate:predicate andSortKey:nil andSortAscending:NO andContext:[FSAppDelegate managedObjectContext]];

if ([existingContactArray count] > 0)
{
    Contact *existingContact = [existingContactArray objectAtIndex:0];

    [CoreDataHelper updateContactWithDictionary:contactDictionary forContactObject:existingContact];
}