Question

这是我的问题。

我正在使用Xcode 7.3.1上的Core Data，Swift 2。我有3张桌子。第一个名为TableX，下一个TableY，最后是TableZ，每个人都有自己的属性。 TableX没有任何关系，TableY与TableX的关系是“To Many”而没有反向;并且TableZ与TableY和反向具有“To Many”的关系。之后，我生成了我的NSManagedObject子类。

我在TableX中添加了4个元素，然后在TableY中添加了1个与TableX中的4个元素相关的寄存器，然后在TableZ中添加了2个元素，每个元素与TableY中的寄存器相关。当我这样做时，TableX中的元素不出现在TableZ的第一个寄存器中，但是它们出现在第二个寄存器中，TableZ中的两个寄存器都正确地保存了TableY中的寄存器。为什么会这样？我添加了我的代码。

func addElementToTableX(idEleX: String)->TableX?{
  let managedObjectContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext

  let fetchRequestTableX = NSFetchRequest(entityName: "TableX")
  let predicateTableX = NSPredicate(format: "tablexid == %@", idEleX)
  fetchRequestTableX.predicate = predicateTableX
  do {
      let fetchedEntitiesTableX = try managedObjectContext.executeFetchRequest(fetchRequestTableX) as! [TableX]
      if (fetchedEntitiesTableX.count == 0){
          let newTableX = NSEntityDescription.insertNewObjectForEntityForName("TableX", inManagedObjectContext: managedObjectContext) as! TableX

         newTableX.tablexid = "saldkjadkj"
         do {
            try newTableX.managedObjectContext!.save()
            print("Saved!")
            return newTableX
         } catch let error as NSError {
            print("Error")
            return nil
         }
      }else{
            print("This element exist")
            return fetchedEntitiesTableX[0]
      }
  } catch {
        return nil
  }            
}


func addElementToTableY(idEleY: String, elementsTableX: [TableX])->TableY?{
  let managedObjectContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext

  let fetchRequestTableY = NSFetchRequest(entityName: "TableY")
  let predicateTableY = NSPredicate(format: "tableyid == %@", idEleY)
  fetchRequestTableY.predicate = predicateTableY
  do {
      let fetchedEntitiesTableY = try managedObjectContext.executeFetchRequest(fetchRequestTableY) as! [TableY]
      if (fetchedEntitiesTableY.count == 0){
          let newTableY = NSEntityDescription.insertNewObjectForEntityForName("TableY", inManagedObjectContext: managedObjectContext) as! TableY

         newTableY.tableyid = "ccbnnzmz"
         newTableY.setValue(NSSet(array: elementsTableX), forKey: "tableX")
         do {
            try newTableY.managedObjectContext!.save()
            print("Saved!")
            return newTableY
         } catch let error as NSError {
            print("Error")
            return nil
         }
      }else{
            print("This element exist")
            return fetchedEntitiesTableY[0]
      }
  } catch {
        return nil
  }            
}

func addElementToTableZ(idEleZ: String, elementsTableY: [TableY])->TableZ?{
  let managedObjectContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext

  let fetchRequestTableZ = NSFetchRequest(entityName: "TableZ")
  let predicateTableZ = NSPredicate(format: "tablezid == %@", idEleZ)
  fetchRequestTableZ.predicate = predicateTableZ
  do {
      let fetchedEntitiesTableZ = try managedObjectContext.executeFetchRequest(fetchRequestTableZ) as! [TableZ]
      if (fetchedEntitiesTableZ.count == 0){
          let newTableZ = NSEntityDescription.insertNewObjectForEntityForName("TableZ", inManagedObjectContext: managedObjectContext) as! TableZ

         newTableZ.tablezid = "ccbnnzmz"
         newTableZ.setValue(NSSet(array: elementsTableZ), forKey: "tableZ")
         do {
            try newTableZ.managedObjectContext!.save()
            print("Saved!")
            return newTableZ
         } catch let error as NSError {
            print("Error")
            return nil
         }
      }else{
            print("This element exist")
            return fetchedEntitiesTableZ[0]
      }
  } catch {
        return nil
  }            
}

Answer 1

我建议使用魔法记录库。它将基于键值编码工作，因此我们可以使用此库实现多对多的关系。

CoreData + Swift 2：多对多关系不适用于三个表

1 个答案: