ios - 核心数据 - 等效于使用类别/示例 - Swift

Question

我想知道如何从本质上为我的 CoreData NSManagedObject 客户端创建一个类别的等价物:

我知道 Extensions 现在是 Swift 中 Categories 的替代品——但是我不确定它们的实现。这是我在下面扣除的内容:

class Client: NSManagedObject {

    @NSManaged var name: String
    @NSManaged var projects: NSSet

}

extension Client {

    func addClientWithName(name:NSString, context:NSManagedObjectContext) -> Client {
        var client:Client = Client();

        // Check for name in the database already exists
        let request:NSFetchRequest = NSFetchRequest(entityName: "Client")
        let sortDescriptor:NSSortDescriptor = NSSortDescriptor(key: "name", ascending: true)
        let sortDescriptorsAry:NSArray = [sortDescriptor]
        request.sortDescriptors = sortDescriptorsAry
        request.predicate = NSPredicate(format: "name = %@", name)

        var error:NSError?
        let matches:NSArray = context.executeFetchRequest(request, error: &error)

        if matches.count == 0 {

            //Add new Client
            var newClient:NSEntityDescription = NSEntityDescription.insertNewObjectForEntityForName("Client", inManagedObjectContext: context) as NSEntityDescription
            newClient.setValue(name, forKey: "name")

            context.save(nil);

        } else {
            client = matches.lastObject as Client
        }

        return client
    }
}

然而，对于这个实现，这是我到目前为止得到的错误:

CoreData: error: Failed to call designated initializer on NSManagedObject class "Ttc9AppName6Client"

关于可能导致此问题的任何想法？

编辑: 这就是我从其他类调用方法的方式:

@IBAction func saveBtnTapped(UIButton) {
    println("save btn tapped")
    var client:Client = Client().addClientWithName("Woofy Face", context: self.managedObjectContext)
}

Answer 1

我认为您的问题与类别/扩展无关。

 var client:Client = Client();

不调用 NSManagedObject 的指定初始值设定项，并且此对象 如果提取请求没有找到匹配的对象，则返回。

在这种情况下，您可能想要返回新创建的对象。

还要注意

insertNewObjectForEntityForName:inManagedObjectContext:

返回托管对象，而不是实体描述。

此外，

var client:Client = Client().addClientWithName(...)

还创建了一个 Client 对象而不使用指定的初始化器。 您应该将方法定义为类方法。

所以你的代码应该是这样的:

 class func addClientWithName(name:NSString, context:NSManagedObjectContext) -> Client {
    var client:Client

    let request:NSFetchRequest = NSFetchRequest(entityName: "Client")
    let sortDescriptor:NSSortDescriptor = NSSortDescriptor(key: "name", ascending: true)
    let sortDescriptorsAry:NSArray = [sortDescriptor]
    request.sortDescriptors = sortDescriptorsAry
    request.predicate = NSPredicate(format: "name = %@", name)

    var error:NSError?
    let matches:NSArray = context.executeFetchRequest(request, error: &error)

    if matches.count == 0 {
        //Add new Client
        client = NSEntityDescription.insertNewObjectForEntityForName("Client", inManagedObjectContext: context) as Client
        client.name = name
        context.save(nil)
    } else {
        client = matches.lastObject as Client
    }
    return client
}

它会被称为

let client:Client = Client.addClientWithName("Woofy Face", context: self.managedObjectContext)