对象之间的核心数据关系 [英] Core Data Relation between Objects
问题描述
我有一个关于如何在Core Data中创建2个NSObject之间的关系的问题。
i have a question about how create a relation between 2 NSObjects in Core Data.
首先我有这个CoreData结构。
First i have this CoreData Structure.
是文件和表单之间的关系。表单可以有多个文件，但一个文件只能有一个表单。
There is a Relationship between files and forms. A form could have multiple files, but one file could only have one form.
我已经创建了NSObjects只有Swift（所以没有桥接头） - 现在有2核心数据NSObject类：
I have created the NSObjects only with Swift (so no Bridging Header) - and have now 2 Core Data NSObject Classes:
class Forms: NSManagedObject {
@NSManaged var uuid: String
@NSManaged var damagenumber: String
@NSManaged var internalnumber: String
@NSManaged var date: NSDate
@NSManaged var name: String
@NSManaged var street: String
@NSManaged var postalcode: String
@NSManaged var city: String
@NSManaged var country: String
@NSManaged var templateJSON: String
@NSManaged var formname: String
@NSManaged var files: NSSet
}
class Files: NSManagedObject {
@NSManaged var url: String
@NSManaged var forms: Forms
}
我的文件在这里作为NSSet。
My files are here as a NSSet.
，我想例如添加一个具有5个文件的表单。所以startet有这样的：
So, i would like for example add a form with 5 files. So startet with something like this:
var request = NSFetchRequest(entityName: "Forms")
request.returnsObjectsAsFaults = false;
let newFormObject = NSEntityDescription.insertNewObjectForEntityForName("Forms", inManagedObjectContext: context) as Forms
newFormObject.setValue(uuid, forKey: "uuid")
......
//插入文件
for index in 0...4 {
var request = NSFetchRequest(entityName: "Files")
request.returnsObjectsAsFaults = false;
let newFileObject = NSEntityDescription.insertNewObjectForEntityForName("Files", inManagedObjectContext: context) as Files
newFileObject.setValue(arrFiles[index], forKey: "url")
}
Ok一切正常。但是：我如何连接这2个对象？如果u使用Obj-C NSObjects而不是Swift我有几个方法添加文件到窗体。
Ok everything works fine. BUT: How do i connect this 2 Objects? If u use Obj-C NSObjects instead of Swift i have a few Methods to add a File to a Form. But how can i do this in Swift only?
如果我有一个关系 - 如何从某个表单中读取所有文件对象？
And if i have a relation - how do i read all File Objects from a certain Form?
编辑：
我现在改变了行：
@NSManaged var files: NSSet
/ p>
to
@NSManaged var files: [Files]
并在循环中使用：
newFormObject.files.append(newFileObject)
这会带来以下错误：
***错误：此进程已调用NSArray-taking方法，如initWithArray :,并在一个NSSet对象中传递。
*** ERROR: this process has called an NSArray-taking method, such as initWithArray:, and passed in an NSSet object. This is being worked-around for now, but will soon cause you grief.
推荐答案
减少您的代码：仅当需要检索对象时设置NSFetchRequests。因此，每次创建新对象时，不需要以下行：
Reduce your code: Set NSFetchRequests only when you need to retrieve objects. Thus, you don't need the following lines every time you create new objects:
//Forms
var request = NSFetchRequest(entityName: "Forms")
request.returnsObjectsAsFaults = false;
//Files
var request = NSFetchRequest(entityName: "Files")
request.returnsObjectsAsFaults = false;
一致性：您已设置NSManagedObject子类。所以使用它们，不要使用键值编码。替换：
Be consistent: You have set NSManagedObject subclasses. So use them and don't use Key Value Coding. Replace:
newFormObject.setValue(uuid, forKey: "uuid")
与：
newFormObject.uuid = uuid
问题：
如何连接此2个对象？
一行代码应该足够你的循环：
A single line of code should be enough at the end of your loop:
newFileObject.forms = newFormObject // where forms is the name of your relationship
问题：
如何从某个表单中读取所有文件对象
how do i read all File Objects from a certain Form
当您需要检索 Files对象表单，你可以执行一个NSFetchRequest（允许你设置谓词，排序等等），或者你可以简单地得到一个NSSet的所有相关对象，如下所示：
When you need to retrieve Files objects of a certain Form, you can perform a NSFetchRequest (that allows you to set predicates, sorts and much more) or you can simply get a NSSet of all your related objects like this:
//Get all Files objects (of a to-many relationship) related to a single Form object
let filesSet = myForm.files as NSSet //where myForm is a Form managedObject
let filesArray = filesSet.allObjects as Array
for obj in filesArray as [Files] {
println(obj.url)
}
这篇关于对象之间的核心数据关系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！
