ios - RestKit 0.20.2 中创建的重复 Core Data 对象

Question

我遇到了一个问题，每次在 RestKit 0.20.2 中执行映射操作时，我都会对 SQLite 数据库进行重复写入。我在网上进行了广泛的查找，似乎找不到与我遇到的问题重复的问题 - 我见过的所有类似问题都集中在使用 RestKit 进行所有操作，而我仅使用 RestKit 进行映射和数据库操作，因为我正在另一个库中进行网络方面的工作。

我有一个唯一的 identificationAttribute 属性集(推文 ID)，并且正在使用通过 RKInMemoryManagedObjectCache 初始化的 managedObjectCache；然而，每次执行映射操作时，我都会在所有内容上得到全面的重复。我用于网络端的库 (STTwitter) 将 JSON 作为数组返回，因此我迭代数组中的每个对象。我还应该执行其他操作吗？我的印象是，在进行任何插入之前，RestKit 会将映射对象中指定的 identificationAttribute 属性与 SQLite 数据库中已有的属性进行比较。当我使用 RKManagedObjectRequestOperation 将其用于另一个项目中的所有内容时，我没有遇到此问题。

这是我设置模型的方法:

-(void)setup
{
self.objectStore = [[RKManagedObjectStore alloc] initWithManagedObjectModel:[self managedObjectModel]];

[self.objectStore createPersistentStoreCoordinator];

NSString *path = [RKApplicationDataDirectory() stringByAppendingPathComponent:@"FoodTruckxxx.sqlite"];
NSLog(@"Setting up store at %@", path);
[self.objectStore addSQLitePersistentStoreAtPath:path
                          fromSeedDatabaseAtPath:nil
                               withConfiguration:nil
                                         options:self.optionsForSQLiteStore
                                           error:nil];

[self.objectStore createManagedObjectContexts];

self.objectStore.managedObjectCache = [[RKInMemoryManagedObjectCache alloc] initWithManagedObjectContext:self.objectStore.persistentStoreManagedObjectContext];
}

这是我执行映射操作的方法:

-(void)performMapping
{
int i = 0;
while (i < self.localCopyOfAllStatuses.count)
{
    RKManagedObjectStore *store = [[FoodTruckDataModel sharedDataModel] objectStore];
    RKEntityMapping *mapping = [ObjectMappings FoodTruckArticleMapping];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"FoodTruck" inManagedObjectContext:store.persistentStoreManagedObjectContext];
    NSManagedObject *newManagedObject = [[NSManagedObject alloc] initWithEntity:entity insertIntoManagedObjectContext:store.persistentStoreManagedObjectContext];
    RKManagedObjectMappingOperationDataSource *mappingDS = [[RKManagedObjectMappingOperationDataSource alloc] initWithManagedObjectContext:store.persistentStoreManagedObjectContext cache:store.managedObjectCache];

    //assign new array to contain to just one object at a time and iterate through it
    NSArray *justOneStatus = [self.localCopyOfAllStatuses objectAtIndex:i];
    RKMappingOperation *operation = [[RKMappingOperation alloc] initWithSourceObject:justOneStatus destinationObject:newManagedObject mapping:mapping];
    operation.dataSource = mappingDS;
    NSError *error = nil;
    [operation performMapping:&error];
    [store.persistentStoreManagedObjectContext save:&error];
    [store.persistentStoreManagedObjectContext saveToPersistentStore:&error];
    i++;
}
}

这是映射:

+(RKEntityMapping *)FoodTruckArticleMapping
{
RKEntityMapping *jsonMapping = [RKEntityMapping mappingForEntityForName:@"FoodTruck" inManagedObjectStore:[[FoodTruckDataModel sharedDataModel] objectStore]];
jsonMapping.identificationAttributes = @[@"tweetID"];

[jsonMapping addAttributeMappingsFromDictionary:@{
 @"text": @"tweet", @"user.screen_name": @"foodTruckName", @"created_at": @"timeStamp", @"id": @"tweetID"}];

return jsonMapping;
}

和here是我日志中的完整操作。任何帮助将不胜感激!

Answer 1

根据此问题的答案on the RestKit Google Group board (我验证有效)，解决方案是不创建 NSManagedObject并分配 nil至destinationObject在我的RKMappingOperation声明。以下是此方法的正确代码，以及我最初问题的答案:

-(void)performMapping
{
    int i = 0;
    while (i < self.localCopyOfAllStatuses.count)
    {
        RKManagedObjectStore *store = [[FoodTruckDataModel sharedDataModel] objectStore];
        RKEntityMapping *mapping = [ObjectMappings FoodTruckArticleMapping];
        NSEntityDescription *entity = [NSEntityDescription entityForName:@"FoodTruck" inManagedObjectContext:store.persistentStoreManagedObjectContext];
        RKManagedObjectMappingOperationDataSource *mappingDS = [[RKManagedObjectMappingOperationDataSource alloc] initWithManagedObjectContext:store.persistentStoreManagedObjectContext cache:store.managedObjectCache];

        //assign new array to contain to just one object at a time and iterate through it
        NSArray *justOneStatus = [self.localCopyOfAllStatuses objectAtIndex:i];
        RKMappingOperation *operation = [[RKMappingOperation alloc] initWithSourceObject:justOneStatus destinationObject:nil mapping:mapping];
        operation.dataSource = mappingDS;
        NSError *error = nil;
        [operation performMapping:&error];
        [store.persistentStoreManagedObjectContext save:&error];
        [store.persistentStoreManagedObjectContext saveToPersistentStore:&error];
        i++;
    }
}

但是，RestKit Google Group 链接中也建议我实现 RKMapperOperation而不是RKMappingOperation,因为这样我就省去了遍历 JSON 响应数组的麻烦。这就是我最终选择的方案，为了提高效率和更好地使用 RestKit，我提出了这个方案:

-(void)performMapping
{
    RKManagedObjectStore *store = [[FoodTruckDataModel sharedDataModel] objectStore];
    RKManagedObjectMappingOperationDataSource *mappingDS = [[RKManagedObjectMappingOperationDataSource alloc] initWithManagedObjectContext:store.persistentStoreManagedObjectContext cache:store.managedObjectCache];
    RKMapperOperation *mapperOperation = [[RKMapperOperation alloc] initWithRepresentation:self.localCopyOfAllStatuses mappingsDictionary:@{ [NSNull null]: [ObjectMappings FoodTruckArticleMapping] }];
    mapperOperation.mappingOperationDataSource = mappingDS;
    NSError *error = nil;
    [mapperOperation execute:&error];
    [store.persistentStoreManagedObjectContext save:&error];
    [store.persistentStoreManagedObjectContext saveToPersistentStore:&error];
}