RestKit relationships not mapping when manually mapping JSON object - ios

Question

I am following some suggested posts on how to map incoming JSON data directly using RKMapperOperation. My entity object is being created in the data store, but without the proper relationships. Interestingly, if I create an object directly using the Core Data methods after I've already mapping incoming JSON (via websockets), the operation seems to "flesh" out my relationships in the incorrect entity.
To sum the order:
JSON data comes into app through a websocket connection
I map it using the below code, but the relationships aren't mapped
I save some other record in the same entity using a locally created (not RestKit) object with Core Data.
My object mapped from JSON now has its relationships attached!
Here is the JSON data:
{
"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
}
}
Here is my mapping function
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
}
Here is the relationship mapping I'm passing to this function:
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
}
Here is how the function gets called when the websocket subscription is notified:
let jsonString = "<the JSON data per above>"
let mappingResult = self.mapEntityFromJson(jsonString, key: "checkin", mapping: self.checkinMapping())
The attendee_id and session_id values should be establishing a relationship with Attendee and Session entities, but when I look at the sqlite data underlying Core Data the relationship columns are blank even though the incoming attendeeId and sessionId fields get mapped. Once I make the other save locally then those relationship columns get mapped.
Any thoughts?
EDIT:
I should add that when a checkin is mapped from a full RestKit call like .getObject or as the result of .postObject then the mapping works with no issues. It is only in the manual mapping I have here that it seems to fall apart.

Answer 1

Here is the final solution which involved much help from #wain and a key point from another post about needing to make the operationQueue wait until all operations are finished or else the mapping process hadn't finished mapping the relationships. So my NSManagedObject was returning with no relationships connected. The combination of a private child context for proper concurrency and saving of data along with the waiting issue fixed the problem. Here is the final mapping code:
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
}
For now we're leaving it with the in-memory cache and don't see the duplicates issue others reported.