Save complex JSON to Core Data in Swift

Question

I want to save the JSON Result from web service to Core data, following is the code for JSON parsing.

if let jsonResult = try JSONSerialization.jsonObject(wi         


        

Answer 1

It's quite easy to decode the JSON directly into Core Data with Decodable

• First of all create extensions of CodingUserInfoKey and JSONDecoder to be able to pass the managed object context

  extension CodingUserInfoKey {
      static let context = CodingUserInfoKey(rawValue: "context")!
  }
  
  extension JSONDecoder {
      convenience init(context: NSManagedObjectContext) {
          self.init()
          self.userInfo[.context] = context
      }
  }
  

• Add conformance to Decodable in both classes

  class Name: NSManagedObject, Decodable {
  
  class ParamDownload: NSManagedObject, Decodable {
  

• In the class Name (not the extension) add

  private enum CodingKeys: String, CodingKey { case name, iin, isOn }
  
  required convenience init(from decoder: Decoder) throws {
      guard let context = decoder.userInfo[.context] as? NSManagedObjectContext else { fatalError("NSManagedObjectContext is missing") }
      let entity = NSEntityDescription.entity(forEntityName: "Name", in: context)!
      self.init(entity: entity, insertInto: context)
      let values = try decoder.container(keyedBy: CodingKeys.self)
      name = try values.decode(String.self, forKey: .name)
      iin = try values.decode(String.self.self, forKey: .iin)
      isOn = try values.decode(Bool.self.self, forKey: .isOn)
  }
  

• In the class ParamDownload (not the extension) add

  private enum CodingKeys: String, CodingKey { case code = "Code", desc = "Desc", names = "iinData" }
  
  required convenience init(from decoder: Decoder) throws {
      guard let context = decoder.userInfo[.context] as? NSManagedObjectContext else { fatalError("NSManagedObjectContext is missing") }
      let entity = NSEntityDescription.entity(forEntityName: "ParamDownload", in: context)!
      self.init(entity: entity, insertInto: context)
      let values = try decoder.container(keyedBy: CodingKeys.self)
      code = try values.decode(String.self, forKey: .code)
      desc = try values.decode(String.self, forKey: .desc)
      names = try values.decode(Set.self, forKey: .names)
      names.forEach { $0.pd = self }
  }
  

To decode the JSON create the Decoder with the convenience initializer

let decoder = JSONDecoder(context: CoreDataStack.sharedInstance.persistentContainer.viewContext)

the init methods handle the relationships.

I recommend to declare the Core Data attributes as much non-optional as possible.
If an attribute must be remain optional replace decode with decodeIfPresent.