swift 3 - create entry with relationship

Question

i working the first time with relationships in core data. what i have now:

let appdelegate = NSApplication.shared().delegate as! AppDelegate
let context = appdel         


        

Answer 1

You have to perform a fetch to check if the person is available.

Then assign the person to the book (to-one relationship) for example

let personName = "John"
let fetchRequest = NSFetchRequest<Person>(entityName: "Person")
let predicate = NSPredicate(format: "name == %@", personName)
fetchRequest.fetchLimit = 1
do {
    let persons = try context.fetch(fetchRequest)
    if let person = persons.first {
        newBook.person = person
    }
} catch {
   print(error)
}

The code takes advantage of the Swift 3 generic types.

Edit:

The declaration of the NSManagedObject subclasses are wrong.

According to your model Person must be

extension Person {
    @NSManaged public var name: String?
    @NSManaged public var books: NSSet
}

and Books must be

extension Book {
    @NSManaged public var title: String?
    @NSManaged public var person: Person?
}

Consider to make at least the name and title attributes non-optional.

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PS: Since you are using NSManagedObject subclasses you can use the property directly with dot notation rather then KVC

newPerson.name = "Max"