generics - Swift - 使用泛型获取方法

Question

想法是使用 Coredata 获取“类型化”数据。

已更新

class func retrieve<T: AnyObject>(entityName:T.Type, sortBy:String? = nil, isAscending:Bool? = true, predicate:NSPredicate? = nil) -> AnyObject[]    {

    println("\(entityName)")
    let request = NSFetchRequest(entityName: "Users")
    request.returnsObjectsAsFaults = false
    if predicate != nil {
        request.predicate = predicate
    }

    if (sortBy != nil){
        var sorter: NSSortDescriptor = NSSortDescriptor(key: sortBy , ascending: isAscending!)
        request.sortDescriptors = [sorter]
    }


    var error: NSError? = nil
    var fetchedResult = myDataModel.managedObjectContext.executeFetchRequest(request, error: &error)
    if !error {
        println("errore: \(error)")
    }


    println("retrieved \(fetchedResult.count) elements for \(entityName)")
    return fetchedResult

}

现在，我上面写的在语法上是正确的，但我相信还有另一种方法可以实现相同的效果，也许更“容易”。我认为这个建议很明确:) 我试图从 entityName 输入参数

获取类名

以下面的方式或类似的方式调用此函数:

 var xx = myDataModel.retrieve(Users.self)

哪里

 Users: NSManagedeObject

你有什么建议吗？

Answer 1

如果，正如 @David 指出的，您将 @objc(ModelClassName) 添加到您的 Model 类中，这是一个简化版本:

func retrieve<T: NSManagedObject>(entityClass:T.Type, sortBy:String? = nil, isAscending:Bool = true, predicate:NSPredicate? = nil) -> T[] {
    let entityName = NSStringFromClass(entityClass)
    let request    = NSFetchRequest(entityName: entityName)

    request.returnsObjectsAsFaults = false
    request.predicate = predicate

    if (sortBy != nil) {
        var sorter = NSSortDescriptor(key:sortBy , ascending:isAscending)
        request.sortDescriptors = [sorter]
    }

    var error: NSError? = nil
    var fetchedResult = myDataModel.managedObjectContext.executeFetchRequest(request, error: &error)
    if !error {
        println("errore: \(error)")
    }

    println("retrieved \(fetchedResult.count) elements for \(entityName)")
    return fetchedResult
}

人们会这样使用它:

@objc(Client)
class Client : NSManagedObject {
    ...    
}

retrieve(Client)  // This would get all clients in the database.