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這是我的問題。CoreData + Swift 2:多對多關係不適用於三張表
我正在使用Xcode 7.3.1上的Core Data,Swift 2。我有3張桌子。第一個名爲TableX,下一個是TableY,最後是TableZ,每個人都有它們的屬性。 TableX沒有任何關係,TableY與TableX的關係是「To Many」且沒有相反的關係;而TableZ與TableY的關係「To Many」與相反。之後,我生成我的NSManagedObject子類。
我在TableX中添加了4個元素,然後我在TableY中添加了1個與TableX中的4個元素相關的寄存器,然後我在TableZ中添加了2個元素,每個元素與TableY中的寄存器相關。當我這樣做時,TableX中的元素不會出現在TableZ的第一個寄存器中,而是出現在第二個寄存器中,TableZ中的兩個寄存器都正確保存了TableY中的寄存器。爲什麼發生這種事我添加了我的代碼。
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
}
}
除非你有很好的理由,否則你不應該指定沒有反轉的關係。請參閱[核心數據編程指南]中的「反向關係」(https://developer.apple.com/library/watchos/documentation/Cocoa/Conceptual/CoreData/HowManagedObjectsarerelated.html#//apple_ref/doc/uid/TP40001075- CH17-SW1)。我懷疑這可能至少是問題的一部分。 – pbasdf