核心数据关系迅速

Question

I am working on iPhone application where I need to implement one to many relationship from one entity to another entity.I have export NSManagedObject subclass from coredata database but could not find relation accessors in core data model file like Objective-C.

Although I'm able to set data in relationship NSSet but this only persist while iPhone app is running. Once I kill and restart the application I didn't get entity relationship for in fetch request from core data.

I am not sure what I am doing wrong. It will be great if anyone can tell me how to set data in NSSet relationship object. Any sample example will be a great help

Here is my core data model files. One folder can content multiple content as folder detail

extension FolderContent {

    @NSManaged var contentID: NSNumber?
    @NSManaged var contentTitle: String?
    @NSManaged var contentType: String?
    @NSManaged var publishDate: String?
    @NSManaged var folderList: NSSet?

}

extension FolderList {

    @NSManaged var folderID: NSNumber?
    @NSManaged var folderName: String?
    @NSManaged var folderDetail: NSSet?

}

func updateFolderList()
{
    // Initialize Fetch Request
    let fetchRequest = NSFetchRequest()

    // Create Entity Description
    let entityDescription = NSEntityDescription.entityForName(FOLDER_LIST, inManagedObjectContext: self.managedObjectContext)

    // Configure Fetch Request
    fetchRequest.entity = entityDescription

    do {
        let result = try self.managedObjectContext.executeFetchRequest(fetchRequest).last as! FolderList

        let content = result.mutableSetValueForKey("folderDetail")
        content.addObject(self.getContent())

          var folderContent:FolderContent = result.folderDetail?.allObjects.first as! FolderContent
        print(folderContent.contentTitle)
        self.save()

        print(result)

    } catch {
        let fetchError = error as NSError
        print(fetchError)
    }

}
    func getContent()->FolderContent
{
    let folderContent = NSEntityDescription.insertNewObjectForEntityForName(FOLDER_CONTENT, inManagedObjectContext: self.managedObjectContext) as! FolderContent
    folderContent.contentID = 1
    folderContent.contentTitle = "Sandeep"
    folderContent.contentType = "Product"
    return folderContent
}

Answer 1

If the relationship of FolderContent and FolderList is defined as

• A FolderContent have many FolderList(s)
• A FolderList only belongs to a FolderContent

---

FolderContent

extension FolderContent {
    @NSManaged var contentID: NSNumber?
    @NSManaged var contentTitle: String?
    @NSManaged var contentType: String?
    @NSManaged var publishDate: String?
    @NSManaged var folderList: Set<FolderList>?
}

FolderList

extension FolderList {
    @NSManaged var folderID: NSNumber?
    @NSManaged var folderName: String?
    @NSManaged var folderDetail: FolderContent?
}

Let say you want to persist the record and its relationship

func persistRecords() {

    // Insert the new records
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedContext = appDelegate.managedObjectContext

    let folderContentEntity = NSEntityDescription.entityForName("FolderContent", inManagedObjectContext: managedContext)
    let folderListEntity = NSEntityDescription.entityForName("FolderList", inManagedObjectContext: managedContext)

    //Create FolderContent record
    let folderContentObject = FolderContent(entity: folderContentEntity!, insertIntoManagedObjectContext: managedContext)
    folderContentObject.setValue(CONTENTID, forKeyPath: "contentID")
    ...

    //Create FolderList record
    let folderListObject = FolderList(entity: folderListEntity!, insertIntoManagedObjectContext: managedContext)
    folderListObject.setValue(FOLDERID, forKeyPath: "folderID")
    ...

    //Set relationship here
    folderListObject.folderDetail = folderContentObject

    do {
      try managedContext.save()
    } catch let error as NSError  {
      print("Could not save \(error), \(error.userInfo)")
    }
  }

Answer 2

I am guessing you did something like folder.folderDetail.addObject . With core data that won't work because core data behind the scenes is doing lots of things to maintain graph integrity. You have to use mutableSetValueForKey to get the set and have core data work its magic.