如何在Core Data Swift的关系中进行简单的连接

Question

我有关系的核心数据：

extension Rating {

    @NSManaged var date: NSString?
    @NSManaged var rating: NSNumber?
    @NSManaged var ratenames: RateNames?

}

extension RateNames {

    @NSManaged var name: String?
    @NSManaged var rating: NSSet?

}

我需要从RateNames中选择所有值，其中所有数据都来自于所选日期的RateNames评级。

例如RateNames数据：

name=a; name=b;

例如RateNames数据：

date=10-02-2016; rating=5; linked to a
date=10-02-2016; rating=3; linked to b
date=09-02-2016; rating=2; linked to a
date=08-02-2016; rating=3; linked to a
date=08-02-2016; rating=1; linked to b

例如我需要08-02-2016的结果 结果应该是：

{(name:a, date:08-02-2016, rating=3), (name:b, date:08-02-2016, rating=1)}

{p 1}}日期的

结果应如下：

09-02-2016

我在结果中也需要b，因为我需要查看它是否为空。

我正在尝试做类似的事情：

{(name:a, date:09-02-2016, rating=2), (name:b, date:nil, rating=nil)}

但无法得到如何实现这个

Answer 1

通过获取Rating对象并使用关系获取相关name对象的RateName，可以更轻松地获得所需内容：

let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext
let fetchRequest = NSFetchRequest(entityName: "Rating")
do {
    let results = try managedContext.executeFetchRequest(fetchRequest) as! [Rating]
    for result in results {
        let name = result.ratenames.name
        let date = result.date
        let rating = result.rating
        print("name:\(name), date:\(date), rating:\(rating)")
    }
}

这将打印与预期结果类似的结果，但不会包含(name:b, date:nil, rating=nil)。

<强>更新

如果要将上述内容限制为给定日期，可以使用谓词作为获取请求：

fetchRequest.predicate = NSPredicate(format:"date == %@", chosenDate)

但是，由于您要包含(name:b, date:nil, rating=nil)，因此您需要获取所有RatingName个对象。每个对象的rating属性将包含与其相关的任何和所有Ratings。所以我认为你需要过滤它们以确定正确的日期：

let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext
let fetchRequest = NSFetchRequest(entityName: "RateNames")
do {
    let results = try managedContext.executeFetchRequest(fetchRequest)
    let datePredicate = NSPredicate(format:"date == %@", chosenDate)
    for result in results {
        let filteredRatings = result.rating.filteredSetUsingPredicate(datePredicate)
        if filteredRatings.count > 0 {
            let rating = filteredRatings.anyObject()
            print("name:\(result.name), date:\(rating.date), rating:\(rating.rating)")
        } else {
            print("name:\(result.name), date:nil, rating:nil")
        }
    }
}

这假设给定日期的每个Rating只能有一个RatingName;如果不是，你将不得不遍历filteredRatings集。

Answer 2

您需要在relationship中设置Datamodel，就像我为以下示例创建的那样

从code我发现你没有提到One-to-Many Relationship。

然后再次创建sub class的{​​{1}}。 NSManageObject会为所有人创建所需的xCode。