核心数据：数据不存储到数据库（swift）

Posted 2023-02-14

【中文标题】核心数据：数据不存储到数据库（swift）

【英文标题】：Core Data: Data does not store to database (swift)

【发布时间】：2016-05-03 01:04:00

【问题描述】：

数据控制者

class DataController 
let model = "GoodiesCoreData"


private lazy var applicationDocumentsDirectory: NSURL = 
    let urls = NSFileManager.defaultManager().URLsForDirectory(NSSearchPathDirectory.DocumentDirectory, inDomains: NSSearchPathDomainMask.UserDomainMask)
    return urls[urls.count-1]
()

// *****
// ***** DocumentDirectory is the recommended place to store users' data *****
// *****



private lazy var managedObjectModel: NSManagedObjectModel = 
    let modelURL = NSBundle.mainBundle().URLForResource(self.model, withExtension: "momd")!
    return NSManagedObjectModel(contentsOfURL: modelURL)!
()


// Store coordinator mediates the object model and the persistent store

private lazy var persistenceStoreCoordinator: NSPersistentStoreCoordinator = 
    let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
    let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent(self.model)

    do 
        let options = [NSMigratePersistentStoresAutomaticallyOption: true]

        try coordinator.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: options)
    
    catch 
        fatalError("Error adding persistence store")
    

    return coordinator
()


lazy var managedObjectContext: NSManagedObjectContext = 
    var context = NSManagedObjectContext(concurrencyType: NSManagedObjectContextConcurrencyType.MainQueueConcurrencyType)
    context.persistentStoreCoordinator = self.persistenceStoreCoordinator
    return context
()


func saveContext() 
    if managedObjectContext.hasChanges 
        do 
            try managedObjectContext.save()
        
        catch 
            print("Error saving context")
            abort()
        
    

我的实体

插入函数

func uploadToCoreData() 
    for goodies in datas //4 datas
        let moc = DataController().managedObjectContext
        let corePhoto = NSEntityDescription.insertNewObjectForEntityForName("Photo", inManagedObjectContext: moc) as! Photo

        let image = UIImageJPEGRepresentation(goodies.croppedPhoto!, 1)
        corePhoto.photo = image
        corePhoto.qty = goodies.value

        let coreUser = NSEntityDescription.insertNewObjectForEntityForName("User", inManagedObjectContext: moc) as! User
        coreUser.userId = userId

        let coreCart = NSEntityDescription.insertNewObjectForEntityForName("Cart", inManagedObjectContext: moc) as! Cart
        coreCart.cartId = cartId
        coreCart.productName = productName
        coreCart.price = price
        coreCart.quantity = quantity
        coreCart.cartToUser = coreUser

        corePhoto.photoToCart = coreCart

        print(corePhoto.qty)

    

    DataController().saveContext()

    let request = NSFetchRequest(entityName: "Photo")
    let photoCount = DataController().managedObjectContext.countForFetchRequest(request, error: NSErrorPointer.init())


    print("total photo: \(photoCount)")

我正在尝试使用uploadToCoreData() 函数插入数据。看起来没问题，因为当我使用它时它不打印“错误保存上下文”，但是当我获取数据时它打印“总照片：0”它应该是 4。我错过了什么？

【参考方案1】：

您正在创建DataController 的多个实例，不要这样做

我建议使用单例类来确保始终访问相同的 Core Data 堆栈组件。

将此添加到DataController 类

class var sharedController : DataController 
  struct Singleton 
    static let instance = DataController()
 
    return Singleton.instance
 

然后将uploadToCoreData()改为

func uploadToCoreData() 
    let dataController = DataController.sharedController
    let moc = dataController.managedObjectContext
    for goodies in datas //4 datas

        let corePhoto = NSEntityDescription.insertNewObjectForEntityForName("Photo", inManagedObjectContext: moc) as! Photo

        let image = UIImageJPEGRepresentation(goodies.croppedPhoto!, 1)
        corePhoto.photo = image
        corePhoto.qty = goodies.value

        let coreUser = NSEntityDescription.insertNewObjectForEntityForName("User", inManagedObjectContext: moc) as! User
        coreUser.userId = userId

        let coreCart = NSEntityDescription.insertNewObjectForEntityForName("Cart", inManagedObjectContext: moc) as! Cart
        coreCart.cartId = cartId
        coreCart.productName = productName
        coreCart.price = price
        coreCart.quantity = quantity
        coreCart.cartToUser = coreUser

        corePhoto.photoToCart = coreCart

        print(corePhoto.qty)

    

    dataController.saveContext()

    let request = NSFetchRequest(entityName: "Photo")
    let photoCount = moc.countForFetchRequest(request, error: NSErrorPointer.init())

    print("total photo: \(photoCount)")