将JSON对象存储到核心数据中

Question

我正尝试将本地核心数据数据库与远程JSON API同步。我使用RestKit将JSON值映射到本地托管对象。这里是一段代码：

- (IBAction)testButtonPressed:(id)sender { 

NSManagedObjectModel *managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil]; 
RKManagedObjectStore *managedObjectStore = [[RKManagedObjectStore alloc] initWithManagedObjectModel:managedObjectModel]; 
NSError *error = nil; 
BOOL success = RKEnsureDirectoryExistsAtPath(RKApplicationDataDirectory(), &error); 
if (! success) { 
    RKLogError(@"Failed to create Application Data Directory at path '%@': %@", RKApplicationDataDirectory(), error); 
} 

// - - - - - - - - Change the path ! 
NSString *path = [RKApplicationDataDirectory() stringByAppendingPathComponent:@"AC.sqlite"]; 
NSPersistentStore *persistentStore = [managedObjectStore addSQLitePersistentStoreAtPath:path 
                   fromSeedDatabaseAtPath:nil 
                     withConfiguration:nil 
                       options:nil 
                        error:&error]; 
if (! persistentStore) { 
    RKLogError(@"Failed adding persistent store at path '%@': %@", path, error); 
} 
[managedObjectStore createManagedObjectContexts]; 

// - - - - - - - - Here we change keys and values 
RKEntityMapping *placeMapping = [RKEntityMapping mappingForEntityForName:@"Place" 
                inManagedObjectStore:managedObjectStore]; 
[placeMapping addAttributeMappingsFromDictionary:@{ 
    @"place_id": @"place_id", 
    @"place_title": @"place_title", 
    @"site": @"site", 
    @"address": @"address", 
    @"phone": @"phone", 
    @"urating": @"urating", 
    @"worktime": @"worktime", 
    @"lat": @"lat", 
    @"lng": @"lng", 
    @"about": @"about", 
    @"discount": @"discount", 
    @"subcategory_title": @"subcategory_title", 
    @"subcategory_id": @"subcategory_id", 
    @"category_title": @"category_title", 
    @"image_url": @"image_url"}]; 


//RKEntityMapping *articleMapping = [RKEntityMapping mappingForEntityForName:@"Article" inManagedObjectStore:managedObjectStore]; 
//[articleMapping addAttributeMappingsFromArray:@[@"title", @"author", @"body"]]; 
//[articleMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:@"categories" toKeyPath:@"categories" withMapping:categoryMapping]]; 


NSIndexSet *statusCodes = RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful); // Anything in 2xx 
// here we need to change too 
RKResponseDescriptor *responseDescriptor = 
    [RKResponseDescriptor responseDescriptorWithMapping:placeMapping 
              pathPattern:nil // @"/articles/:articleID" 
               keyPath:@"data.place_list" 
              statusCodes:statusCodes]; 

NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://allocentral.api.v1.ladybirdapps.com/place/?access_token=19f2a8d8f31d0649ea19d478e96f9f89b&category_id=1&limit=10"]]; 

RKManagedObjectRequestOperation *operation = [[RKManagedObjectRequestOperation alloc] initWithRequest:request 
                        responseDescriptors:@[responseDescriptor]]; 

operation.managedObjectContext = managedObjectStore.mainQueueManagedObjectContext; 
operation.managedObjectCache = managedObjectStore.managedObjectCache; 

[operation setCompletionBlockWithSuccess:^(RKObjectRequestOperation *operation, RKMappingResult *result) { 
    NSLog(@" successfull mapping "); 
    [self refreshContent]; 

} failure:^(RKObjectRequestOperation *operation, NSError *error) { 
    NSLog(@"Failed with error: %@", [error localizedDescription]); 
}]; 

NSOperationQueue *operationQueue = [NSOperationQueue new]; 
[operationQueue addOperation:operation]; 
} 

- (void) refreshContent { 
// perform fetch 
NSError *error = nil; 
if (![self.fetchedResultsController performFetch:&error]) { 
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]); 
    abort(); 
} 
// reload data 
[self.tableView reloadData]; 
} 

它完美的作品，并得到核心数据中的所有对象，并将它们存储，但如果某些对象是在服务器上删除，他们不是在JSON响应，他们留在detebase。我如何使restkit清除不在响应中的对象？ thx

Answer 1

无论何时，当您从服务器收到新的JSON响应时，都应该照常处理它，并将新条目添加到Core Data对象中。

然后遍历Core Data对象，并检查它们是否包含在JSON中（使用任何适合您的对象的方法），如果没有，请删除它们。

或者，如果您使用JSON传递某种ID，则可以在将对象添加到Core Data的同时将每个ID存储在NSArray中。然后对与数组中的ID不匹配的任何Core Data对象执行谓词搜索，并删除它们。

哪个更好取决于你是否有更多的新/现有物品或更多的待删除物品。