CoreData - 使用类别w /示例 - Swift的等效 [英] CoreData - Equivalent of Using Categories w/ Example - Swift

问题描述

我想知道如何基本上为我的CoreData NSManagedObject客户端创建相当于一个类别：

我知道扩展现在是Swift中类别的替换 - 但是我不确定它们的实现。这是我在下面扣除的：

  class Client：NSManagedObject {
 
 @NSManaged var name： String 
 @NSManaged var projects：NSSet 
 
} 
 
扩展客户端{
 
 func addClientWithName（name：NSString，context：NSManagedObjectContext） - >客户端{
 var client：Client = Client（）; 
 
 //检查数据库中的名称是否已经存在
 let request：NSFetchRequest = NSFetchRequest（entityName：Client）
 let sortDescriptor：NSSortDescriptor = NSSortDescriptor ，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）
 
如果matches.count == 0 {
 
 //添加新客户
 var newClient：NSEntityDescription = NSEntityDescription.insertNewObjectForEntityForName（Client，inManagedObjectContext：context）as NSEntityDescription 
 newClient.setValue（name，forKey：name）
 
 context.save （零）; 
 
} else {
 client = matches.lastObject as Client 
} 
 
返回客户端
} 
} 
 
 
 
 
但是，这是我到目前为止的错误：
  CoreData：错误：无法调用NSManagedObject类Ttc9AppName6Client上的指定初始化程序
  
有什么可能导致这种情况的想法？ 
 
 
 
 编辑：
这是我从其他类调用方法的方法：
  @IBAction func saveBtnTapped（UIButton）{
 println（save btn tapped）
 var client：Client = Client（）。addClientWithName Woofy Face，context：self.managedObjectContext）
} 
  
 
 
解决方案
我认为你的问题与类别/扩展无关。
  var client：Client = Client 
  
不会调用 NSManagedObject的指定初始化程序，如果获取请求没有找到匹配的对象，则返回此对象
。
 
 
 
你可能想要的是返回新的
 
 
 
请注意
  insertNewObjectForEntityForName： inManagedObjectContext：
  
返回受管对象，而不是实体描述。
 
 
 
此外，
  var client：Client = Client（）。addClientWithName $ b  
还创建一个Client对象，而不使用指定的初始化程序。 
您应该将方法定义为类方法。
 
 
 
因此，您的代码应如下所示：
  class func addClientWithName（name：NSString，context：NSManagedObjectContext） - >客户端{
 var client：Client 
 
让请求：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）
 
如果matches.count == 0 {
 //添加新客户端
 client = NSEntityDescription.insertNewObjectForEntityForName（Client，inManagedObjectContext：context）as Client 
 client.name = name 
 context.save（nil）
} else {
 client = matches。 lastObject as Client 
} 
 return client 
} 
  
将被称为
  let client：Client = Client.addClientWithName（Woofy Face，context：self.managedObjectContext）
  
 
I'm wondering how to essentially create the equivalent of a Category for my CoreData NSManagedObject Client below:

I understand that Extensions are now the replacement of Categories in Swift - however am unsure of their implementation. Here is what I have deducted below:
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
    }
}
With this implementation however, this is the error i get so far:
CoreData: error: Failed to call designated initializer on NSManagedObject class "Ttc9AppName6Client"
Any ideas on what could be causing this? 

Edit:
This is how i call the method from my other class:
@IBAction func saveBtnTapped(UIButton) {
    println("save btn tapped")
    var client:Client = Client().addClientWithName("Woofy Face", context: self.managedObjectContext)
}

解决方案
I think your problem is unrelated to categories/extensions.
 var client:Client = Client();
does not call the designated initializer of NSManagedObject, and this object
is returned if the fetch request found no matching object.

What you probably want is to return the newly created object in that case.

Note also that
insertNewObjectForEntityForName:inManagedObjectContext:
returns a managed object, not an entity description.

In addition, 
var client:Client = Client().addClientWithName(...)
also creates a Client object without using the designated initializer.
You should define the method as a class method instead.

So your code should look like this:
 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
}
and it would be called as
let client:Client = Client.addClientWithName("Woofy Face", context: self.managedObjectContext)


                        
这篇关于CoreData  - 使用类别w /示例 -  Swift的等效的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！