swift core data fetching relationship - core-data

Question

I'm a little bit confused try to fetch relation data from coredata in swift
Person Entity
contains the name of person and Unique Id. The relation with Books is ONE to Many
For example
Person Entity:
idPerson = 25 - namePerson = John
idPerson = 26 - namePerson = Steve
Books Entity contains the title of books, Unique Id for the book and a relation ID with person (personBook). The relation with Person is ONE to ONE
For example
Books Entity:
idBook = 2543 - titleBook = title one - personBook = 25
idBook = 2544 - titleBook = title two - personBook = 25
idBook = 2545 - titleBook = title three - personBook = 26
here my data model screenshot: (no image because i have no reputation)
Person class
#objc(Person)
class Person: NSManagedObject {
#NSManaged var idPerson: String
#NSManaged var namePerson: String
#NSManaged var booksRel: NSSet
}
Books class
#objc(Books)
class Books: NSManagedObject {
#NSManaged var bookTitle: String
#NSManaged var idBook: String
#NSManaged var personBook: String
#NSManaged var personRel: Person
}
Fetch code
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
///////////////////////////////////////
}
is possibile to fetch for every book the related namePerson based on namePerson = personBook ?
Thank you very much!

Answer 1

You don't need a property personBook for your Books entity.
Let's create a Person managedObject (using Swift 1.0):
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()
}
When you create a Books managedObject, you can link it to person like this:
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()
}
Now, when you want to make a fetch on Books, you can do like this:
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)
}

Answer 2

If I have understood your question / data structure correctly, you will want to do something like:
let fetchRequest = NSFetchRequest(entityName: "Books")
let bookPersonPredicate = NSPredicate(format: "personRel.idPerson == %#", person.idPerson)
fetchRequest.predicate = bookPersonPredicate