iOS核心数据可转换

Question

I am relatively new to iOS CoreData implementation. Here is my problem:

I have an entity which has an 'assets' field that may contain one or many different types of objects. It is in a sub-object of another. What is the best way to store this and how do I retrieve it.

My pseudo code example:

extension Group (
    @NSManaged public var created: NSDate?
    @NSManaged public var type: String?
    @NSManaged public var people: NSSet?
}

extension Person {
    @NSManaged public var created: NSDate?
    @NSManaged public var type: String?
    @NSManaged public var asset: NSObject?  //marked as transformable in data model
}

In the Person.asset it can be one or a combination of several different class of objects:

extension Car {..}
extension House { ...} 
etc. 

My current method of saving is creating the individual type of asset and add to the person;

let myGroup = Group(...)
let person1 = Person(...)
let hisCar = Car(..) 
person1.asset = hisCar
myGroup.addPersonObject(person: person1)

let person2 = Person(...)
let hisHouse = House(...) 
person2.asset = hisHouse
myGroup.addPersonObject(person: person2)

BEFORE I save context the following seems to work and I can access the Person objects by:

let peopleInGroup = Group.people!
for case let person as Person in peopleInGroup {
    if person.type != "" {
        print (person.type as! String)
    }
}

Until I save the context and Reload the application. On load of the application I fetch Group object and then try to execute the same code above. It appears to be pointing at the right person object, but fails on the person.type line and I end up wit an error: [error] error: exception handling request: , -[Asset initWithCoder:]: unrecognized selector sent to instance 0x60c00027e040 with userInfo of (null)

I believe I might need to do some sort of encoding on the asset field when I am saving and fetching? The error is referencing the asset even though I am trying to access the type property on the person. Thanks in advance for any help.

Answer 1

Transformable attributes work by using NSCoding on the attribute value. It doesn't really matter if asset has multiple types as long as all of them conform to NSCoding . If adding that to your various types is a problem, you'll have to find some other way to save the asset info.