我有点困惑尝试从swift中的coredata获取关系数据
人员实体 包含人名和唯一ID。与书籍的关系是一对多
例如
Person Entity:
idPerson = 25 - namePerson = John
idPerson = 26 - namePerson = Steve
图书实体包含图书标题,图书的唯一标识以及与人的关系标识(personBook)。与人的关系是一对一的 例如
Books Entity:
idBook = 2543 - titleBook = title one - personBook = 25
idBook = 2544 - titleBook = title two - personBook = 25
idBook = 2545 - titleBook = title three - personBook = 26
这里我的数据模型截图:(没有图片,因为我没有声誉)
人类
@objc(Person)
class Person: NSManagedObject {
@NSManaged var idPerson: String
@NSManaged var namePerson: String
@NSManaged var booksRel: NSSet
}
图书班
@objc(Books)
class Books: NSManagedObject {
@NSManaged var bookTitle: String
@NSManaged var idBook: String
@NSManaged var personBook: String
@NSManaged var personRel: Person
}
获取代码
let appDel:AppDelegate = UIApplication.sharedApplication().delegate as AppDelegate
let context:NSManagedObjectContext = appDel.managedObjectContext!
let request = NSFetchRequest(entityName: "Books")
request.returnsObjectsAsFaults = false
request.fetchLimit = 30
////////////////////////////
// CODE TO JOIN Person entity WHERE personBook = idPerson
////////////////////////////
var results:NSArray = context.executeFetchRequest(request, error: nil)!
for temp in results {
var data = temp as Books
///////////////////////////////////////
//println(data.namePerson) ----> not working
///////////////////////////////////////
}
是否有可能根据namePerson = personBook为每本书获取相关的namePerson?
非常感谢!
答案 0 :(得分:10)
您的personBook
实体不需要属性Books
。
让我们创建一个Person
managedObject:
let person = NSEntityDescription.insertNewObjectForEntityForName("Person", inManagedObjectContext: context) as Person
person.idPerson = 23
person.namePerson = "John"
var error: NSError?
if !context.save(&error) {
println("Unresolved error \(error), \(error!.userInfo)")
abort()
}
创建Books
managedObject时,可以将其链接到person
,如下所示:
let book = NSEntityDescription.insertNewObjectForEntityForName("Books", inManagedObjectContext: context) as Books
book.bookTitle = "My book Title"
book.idBook = 2547
book.personRel = person
var error: NSError?
if !context.save(&error) {
println("Unresolved error \(error), \(error!.userInfo)")
abort()
}
现在,当你想在Books
上进行抓取时,你可以这样做:
let fetchRequest = NSFetchRequest(entityName: "Books")
var error: NSError?
var booksArray = context.executeFetchRequest(fetchRequest, error:&error)
if let error = error {
println("Unresolved error \(error), \(error.userInfo)")
abort()
}
for book in booksArray as [Books] {
let person = book.personRel as Person
println(person.namePerson)
println(person.idPerson)
}
答案 1 :(得分:1)
如果我已正确理解您的问题/数据结构,您将需要执行以下操作:
let fetchRequest = NSFetchRequest(entityName: "Books")
let bookPersonPredicate = NSPredicate(format: "personRel.idPerson == %@", person.idPerson)
fetchRequest.predicate = bookPersonPredicate