Swift: Insert codable object into Core Data

Question

I'm getting a response from an API and decoding the response like this:

struct MyStuff: Codable {
    let name: String
    let quantity: Int
    let location: String
}

And I have instance an Entity to map MyStuff:

@objc(Stuff)
public class Stuff: NSManagedObject {
}

extension Stuff {
    @nonobjc public class func fetchRequest() -> NSFetchRequest<Stuff> {
        return NSFetchRequest<Stuff>(entityName: "Stuff")
    }
    @NSManaged public var name: String?
    @NSManaged public var quantity: Int64
    @NSManaged public var location: String?
}

My question is, when I have the response of type MyStuff there is a way to loop thru the keys and map the values to core data?

for example:

let myStuff = MyStuff(name: "table", quantity: 1, location: "kitchen")

let myStuff = MyStuff(name: "table", quantity: 1, location: "kitchen")
        for chidren in Mirror(reflecting: myStuff).children {
            print(chidren.label)
            print(chidren.value)
            /*
             insert values to core data
             */
        }

I'll really appreciate your help

Answer 1

A smart solution is to adopt Decodable in Stuff

Write an extension of CodingUserInfoKey and JSONDecoder

extension CodingUserInfoKey {
    static let context = CodingUserInfoKey(rawValue: "context")!
}

extension JSONDecoder {
    convenience init(context: NSManagedObjectContext) {
        self.init()
        self.userInfo[.context] = context
    }
}

In Stuff adopt Decodable and implement init(from:), it must be implemented in the class, not in the extension

@objc(Stuff)
public class Stuff: NSManagedObject, Decodable {

    private enum CodingKeys: String, CodingKey { case name, quantity, location }
    
    public required convenience init(from decoder: Decoder) throws {
        guard let context = decoder.userInfo[.context] as? NSManagedObjectContext else { fatalError("Error: context doesn't exist!") }
        let entity = NSEntityDescription.entity(forEntityName: "Stuff", in: context)!
        self.init(entity: entity, insertInto: context)
        let values = try decoder.container(keyedBy: CodingKeys.self)
        name = try values.decodeIfPresent(String.self, forKey: .name)
        quantity = try values.decodeIfPresent(Int64.self, forKey: .quantity) ?? 0
        location = try values.decodeIfPresent(String.self, forKey: .location)
    }
}

To decode the JSON you have to initialize the decoder with the convenience initializer

let decoder = JSONDecoder(context: context)

where context is the current NSManagedObjectContext instance.

Now you can create Stuff instances directly from the JSON.