核心数据优化

Question

我在NSDictionary中有一个很大的用户列表，它的结构如下：

        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，则更新该用户。否则，创建一个新用户。我做这件事的方式是有效的，但它非常慢。下面是我的代码：

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.");
    }
}

下面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;
}

有没有人能给我举个例子，告诉我如何以一种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

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.");
        }
    }
}

使用

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

另外，您是否在核心数据模型中定义了一些imageURL、imageThumb和locationName的默认值？如果不是，为什么要检查空值(两次)？

奖励：

消除countForEntity:withPredicate:andContext: call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];
}

Answer 2

您需要了解fetch请求是昂贵的(它需要运行SQL和执行I/O)。我不知道你的CoreDataHelper是从哪里来的，但它会做一些昂贵的NSFetchRequest。您可以构造一个NSFetchRequest，它将告诉您哪些对象已经存在。这将把成本从O(N)降低到O(1)。

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

如上所述，将保存移出循环。但如果你正在更新添加一个多个对象，你可能需要时不时地保存。