带有嵌套项的 RestKit 动态映射

Question

我在为一组结果配置动态映射时遇到问题。我想要映射的结果对象嵌入在描述封闭对象类型的“容器”中。

我有类似于以下的 JSON：

"list": {
    "name": ""
    "item_infos": [
    {
        "type": "TaskItem",
        "item": {
            "id": 0
            "title": "A Task Item",
            "task": "..."
        }
        "url": "..."
    },
    {
        "type": "ReminderItem",
        "item": {
            "id": 0
            "title": "A Reminder Item",
            "reminder": "..."
        }
        "url": "..."
    }]
}

我想将其映射为具有Items 数组的List 对象，其中每个项目可能属于不同类型。不同的types 是有限且已知的。

class List: NSManagedObject {
    @NSManaged var name: String
    @NSManaged var items: NSOrderedSet
}

class Item: NSManagedObject {
    @NSManaged var identifier: Int32
    @NSManaged var title: String

    // Each mappable `Item` is responsible for providing its own
    // mapping object. It's overridden in the subclasses below.
    class func responseMappingForManagedObjectStore(dos: RKManagedObjectStore) -> RKEntityMapping { ... }
}

class TaskItem: Item {
    @NSManaged var task: String
}

class ReminderItem: Item {
    @NSManaged var reminder: String
}

如何使用RKDynamicMapping 直接在列表下映射嵌入的item，同时仍然使用type 字段？我正在尝试按照这些方式进行响应映射：

let listMapping = RKEntityMapping(forEntityForName: "List", inManagedObjectStore: store)
responseMapping.addAttributeMappingsFromDictionary(["name": "title"])

let dynamicItemMapping = RKDynamicMapping()
dynamicItemMapping.setObjectMappingForRepresentationBlock { representation in

    let itemMapping: RKEntityMapping

    switch representation.valueForKeyPath("type") as? String {
    case .Some("TaskItem"):     itemMapping = TaskItem.responseMappingForManagedObjectStore(objectStore)
    case .Some("ReminderItem"): itemMapping = ReminderItem.responseMappingForManagedObjectStore(objectStore)
    default:                    return nil

    // This is the bit I'm failing to solve. How can I return a mapping
    // that essentially "skips" a level of the JSON, and just maps the
    // embedded `item`, not the `item_info`.
    let itemInfoMapping = RKObjectMapping(forClass: NSMutableDictionary.self)
    itemInfoMapping.addRelationshipMappingWithSourceKeyPath("item", mapping: itemMapping)
    return itemInfoMapping
}

listMapping.addPropertyMapping(RKRelationshipMapping(
    fromKeyPath: "item_infos",
    toKeyPath:   "items",
    withMapping: dynamicItemMapping))

使用此映射，会引发异常：

-[__NSDictionaryM _isKindOfEntity:]: unrecognized selector sent to instance 0x7fd2603cb400

这并不让我感到惊讶，因为动态映射的设置方式无论如何都感觉不对 - 我正在寻找一种方法来“跳过” JSON 的一个级别并且只映射嵌入的 @987654331 @。

另一种尝试是将fromKeyPath 完全指定为"item_infos.item" 与listMapping 的关系，但是我不能使用动态映射块中的type 字段来确定要使用的Item 映射的类型：

// ...
dynamicItemMapping.setObjectMappingForRepresentationBlock { representation in
    // `type` inaccessible from the nested item representation
    switch representation.valueForKeyPath("type") as? String {
    case .Some("TaskItem"):     return TaskItem.responseMappingForManagedObjectStore(objectStore)
    case .Some("ReminderItem"): return ReminderItem.responseMappingForManagedObjectStore(objectStore)
    default:                    return nil
}

listMapping.addPropertyMapping(RKRelationshipMapping(
    fromKeyPath: "item_infos.item",
    toKeyPath:   "items",
    withMapping: dynamicItemMapping))

Answer 1

您不能完全按照您的意愿去做，因为您将核心数据关系连接到将包含托管对象的字典数组。

最简单的解决方案是通过在源键（路径）的开头添加item.，将您的跳过逻辑从其所在位置取出并创建托管对象（任务和提醒）的所有映射。所以

"item.title" : "title"