Core Data可用于保存Codable Struct吗？

Question

I'm struggling with learning Core Data and was wondering if it's even possible to save a struct that adheres to the Codable protocol to Core Data? Essentially, there is a main struct called "Stories" that links to other structs as well.

The basic structure of my model is:

class GetStories : Codable {

typealias NetworkResponse = (Data?, Error?)->Void
typealias ReadyToSave = ()->Void
typealias RefreshTableView = ()->Void

// MARK: - Instance variables
var dataReturnedByServer : Data?
var stories : Stories?
var delegate: GetStoriesDelegate?  // the delegate stops becoming nil when you assign it as the delegate for ViewController.swift
var coverImages : [UIImage]?

// MARK: - Structs
struct Stories : Codable {
    let userStories : [Story]
    let nextURL : URL
    enum CodingKeys: String, CodingKey {
        case userStories = "stories"
        case nextURL = "nextUrl"
    }
}
struct User : Codable {
    let userName : String
    let userAvatar : String
    let userFullName : String
    enum CodingKeys : String, CodingKey{
        case userName = "name"
        case userAvatar = "avatar"
        case userFullName = "fullname"
    }
}
struct Story : Codable {
    let storyID : String
    let storyTitle : String
    let storyUser : User
    let storyCoverImageURL : String
    enum CodingKeys : String, CodingKey{
        case storyID = "id"
        case storyTitle = "title"
        case storyUser = "user"
        case storyCoverImageURL = "cover"
    }
}

... and then there are some other functions.

From what I've read, the struct needs to be converted to classes themselves so that they can derive from NSManagedObject. Is that the best solution to use Core Data to save the "Stories" struct?

Answer 1

Not directly but there are some options.

I will present the one I am using:

You can create model in CoreData similar to your struct with suffix ManagedObject (physically its ManagedObject as it's used by CoreData only), then you can extend the actual ManagedObject and store there your struct.

The extension for User should look like this:

struct User : Codable {
    let userName : String
    let userAvatar : String
    let userFullName : String
}

extension UserManagedObject {
    var model: User {
        get {
            return User(userName: userName!, userAvatar: userAvatar!, userFullName: userFullName!)
        }
        set {
            self.userName = newValue.userName
            self.userAvatar = newValue.userAvatar
            self.userFullName = newValue.userFullName
        }
    }
}

This solution expects you to make ManagedObject models in CoreData first. You can also make the relation ship 1:n and n:n it just takes more time to do it but logic is the same as presented on UserManagedObject .

Answer 2

Core Data uses NSManagedObjects or subclasses of NSManagedObject to store data in its backing store, typically a SQLite store. NSManagedObject is a class not a struct, so if you want to use structs and then save data in Core Data you would need to write some code to copy the data from the struct to a NSManagedObject.

The preference in Swift is to use structs over classes where possible but if you are working with Core Data it may make more sense to be defining your data as NSManagedObjects (and perhaps making the NSManagedObject subclass codable - google core data and cobable and you'll find a bunch of articles including this one .