Question

我正在关注如何使用RKMapperOperation直接映射传入的JSON数据的一些建议帖子。我的实体对象是在数据存储中创建的，但没有正确的关系。有趣的是，如果我在映射了传入的JSON（通过websockets）后直接使用Core Data方法创建了一个对象，那么该操作似乎会“充实”我在不正确实体中的关系。

总结顺序：

JSON数据通过websocket连接进入应用程序
我使用下面的代码映射它，但没有映射关系
我使用本地创建的（而不是RestKit）对象与Core Data在同一实体中保存了一些其他记录。
我从JSON映射的对象现在已经附加了它的关系！

这是JSON数据：

{
    "checkin": {
        "session_id": 1,
        "attendee_id": 70,
        "source": "list",
        "created_at": "2015-03-26 11:53:08",
        "cache_id": "9234d700852df5c7402b87adf6ecfc19",
        "checkout": "0",
        "updated_at": "2015-03-27 03:53:09",
        "id": 359
    }
}

这是我的映射函数

func mapEntityFromJson(JSONString: String, key: String, mapping: RKEntityMapping!) -> NSManagedObject? {
    let MIMEType = "application/json"
    var error: NSError? = nil
    let data = JSONString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
    let jsonDictionary: NSDictionary = NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers, error: &error) as NSDictionary
    let parsedData: AnyObject! = RKMIMETypeSerialization.objectFromData(data, MIMEType: MIMEType, error: &error)
    if (parsedData == nil && error != nil) {
        // Parser error...
        return nil
    }

    let mappingsDictionary = [ key: mapping ]

    let mappingDS = RKManagedObjectMappingOperationDataSource(managedObjectContext: self.objectStore.persistentStoreManagedObjectContext, cache: self.objectStore.managedObjectCache)

    let mapper = RKMapperOperation(representation: parsedData, mappingsDictionary: mappingsDictionary)
    mapper.mappingOperationDataSource = mappingDS
    var mappingError: NSError? = nil
    let isMapped = mapper.execute(&mappingError)
    if (isMapped && mappingError == nil) {
        // Trying to save twice per some other example
        self.objectStore.persistentStoreManagedObjectContext.save(&error)
        self.objectStore.persistentStoreManagedObjectContext.saveToPersistentStore(&error)
        let result = mapper.mappingResult.firstObject() as NSManagedObject
                    return result
    }
    return nil
}

这是我传递给这个函数的关系映射：

func checkinMapping() -> RKEntityMapping {
    let checkinMapping = RKEntityMapping(forEntityForName: "Checkin", inManagedObjectStore: objectStore)
    let checkinDictionary = ["source": "source", "checkout": "checkout", "cache_id": "cacheId", "attendee_id": "attendeeId", "session_id": "sessionId"]

    checkinMapping.addAttributeMappingsFromDictionary(baseRecordDictionary)
    checkinMapping.addAttributeMappingsFromDictionary(checkinDictionary)
    checkinMapping.addConnectionForRelationship("attendee", connectedBy: ["attendeeId": "id"])
    checkinMapping.addConnectionForRelationship("session", connectedBy: ["sessionId": "id"])
    checkinMapping.identificationAttributes = ["cacheId"]
    checkinMapping.setDefaultValueForMissingAttributes = true

    return checkinMapping
}

以下是通知websocket订阅时函数的调用方式：

let jsonString = "<the JSON data per above>"
let mappingResult = self.mapEntityFromJson(jsonString, key: "checkin", mapping: self.checkinMapping())

attendee_id和session_id值应该与Attendee和Session实体建立关系，但是当我查看基础Core数据的sqlite数据时，关系列是即使传入的attendeeId和sessionId字段已映射，也会显示空白一旦我在本地进行另一次保存，那么这些关系列就会被映射。

有什么想法吗？

编辑：我应该补充一点，当从一个完整的RestKit调用（如.getObject）或.postObject的结果映射checkin时，映射可以正常工作。只有在我在这里的手动映射中，它似乎才会分崩离析。

Answer 1

这是最终的解决方案，其中涉及@wain的大量帮助以及另一篇关于需要使operationQueue等待所有操作完成或者映射过程尚未完成映射关系的帖子的关键点。所以我的NSManagedObject返回时没有连接关系。正确并发和保存数据的私有子上下文与等待问题的组合解决了问题。这是最终的映射代码：

func mapEntityFromJson(JSONString: String, key: String, mapping: RKEntityMapping!) -> NSManagedObject? {
    let MIMEType = "application/json"
    var error: NSError? = nil
    let data = JSONString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
    let jsonDictionary: NSDictionary = NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers, error: &error) as NSDictionary
    let parsedData: AnyObject! = RKMIMETypeSerialization.objectFromData(data, MIMEType: MIMEType, error: &error)
    if (parsedData == nil && error != nil) {
        // Parser error...
        return nil
    }

    let mapperContext = self.objectStore.newChildManagedObjectContextWithConcurrencyType(NSManagedObjectContextConcurrencyType.PrivateQueueConcurrencyType, tracksChanges: true)

    let mappingsDictionary = [ key: mapping ]

    let mappingDS = RKManagedObjectMappingOperationDataSource(managedObjectContext: mapperContext, cache: self.objectStore.managedObjectCache)
    var mappingResult: RKMappingResult? = nil
    var result: NSManagedObject? = nil

    let mapper = RKMapperOperation(representation: parsedData, mappingsDictionary: mappingsDictionary)
    mappingDS.operationQueue = self.operationQueue
    mappingDS.parentOperation = mapper
    mapper.mappingOperationDataSource = mappingDS
    var mappingError: NSError? = nil
    let isMapped = mapper.execute(&mappingError)
    // Necessary to wait for relationships to map.
    if self.operationQueue!.operationCount > 0 {
        self.operationQueue!.waitUntilAllOperationsAreFinished()
    }
    if (isMapped && mappingError == nil) {
        mapperContext.saveToPersistentStore(&error)
        mappingResult = mapper.mappingResult
    }

    if mappingResult != nil {
        result = mappingResult!.firstObject() as? NSManagedObject
    }

    return result
}

现在我们将它留在内存缓存中，并且看不到其他人报告的重复项。

手动映射JSON对象时，RestKit关系不映射

1 个答案: