Question

我想知道如何在下面为我的CoreData NSManagedObject客户端创建一个类别的等价物：

据我所知，Extensions现在取代了Swift中的类别 - 但不确定它们的实现。以下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，通过这种实现，这是我到目前为止所犯的错误：

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

关于可能导致这种情况的任何想法？

修改这就是我从其他班级调用该方法的方法：

@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和此对象的指定初始值设定项如果获取请求未找到匹配的对象，则返回。

你可能想要的是在这种情况下返回新创建的对象。

另请注意

insertNewObjectForEntityForName:inManagedObjectContext:

返回托管对象，而不是实体描述。

此外，

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

还可以在不使用指定的初始值设定项的情况下创建Client对象。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
}

，它将被称为

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

核心数据 - 使用/示例使用类别的等价物 - Swift

1 个答案: