CoreDataCodable

CoreDataCodable contains protocols and extensions for making Core Data play nice with Swift's Codable protocols

Requirements

• iOS 10+
• macOS 10.12+ (Sierra)
• Swift 4+
• Xcode 10.2

Installation

Cocoapods

You want to add pod 'CoreDataCodable', '~> 1.0' similar to the following to your Podfile:

target 'MyApp' do
  pod 'CoreDataCodable', '~> 1.0'
end

Then run pod install inside your terminal, or from CocoaPods.app.

Alternatively to give it a test run, run the command:

$ pod try CoreDataCodable

Carthage

To integrate CoreDataCodable into your Xcode project using Carthage, specify it in your Cartfile:

github "peterringset/CoreDataCodable" ~> 1.0

Then run carthage update inside your terminal.

Usage

To make an NSManagedObject-subclass be parsable through Decodable you can declare conformance to DecodableManagedObject, and implement the protocol:

import CoreData
import CoreDataCodable

extension Employee: DecodableManagedObject {

    public enum CodingKeys: String, CodingKey {
        case firstName
        case lastName
        case title
        case telephone
        case imageURL
    }

    public func setValues(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        firstName = try container.decode(String.self, forKey: .firstName)
        lastName = try container.decode(String.self, forKey: .lastName)
        title = try container.decode(String.self, forKey: .title)
        telephone = try container.decode(String.self, forKey: .telephone)
        imageURL = try container.decode(String.self, forKey: .imageURL)
    }

}

To use this together with Swift's JSONDecoder, you have to assign a managed object context instance to the decoders userInfo:

let decoder = JSONDecoder()
decoder.userInfo[.managedObjectContext] = persistentContainer.newBackgroundContext()
let employees = try decoder.decode(Employee.self, from: json)

This will insert the object into the provided context. Note that it is still up to you to save the context after parsing is done.

Insert or update existing objects

If you have an application where you will download entities that you already have in a local database, you can use ManagedObjectUpsert to help you manage that. This requires the entity class to conform to FetchableManagedObject, a protocol that tells us how to query the local database for an existing instance.

extension Employee {
    public typealias FetchableCodingKeys = CodingKeys
    public typealias Identifier = String
    public static var identifierKey: Employee.CodingKeys {
        return .lastName
    }
}

Then you can modify the decoding call to be

let upsert = try decoder.decode(ManagedObjectUpsert<Employee>.self, from: json)
let employee = upsert.object

There is also a corresponding struct called ManagedObjectsUpsert for decoding an array of objects with the upsert mechanism.

Core data codegen

CoreDataCodable is compatible with Core Data's codegen feature, but you should be aware that if you're using custom types (that are transformable), you will have to use the Manual/None alternatives. You can still get Xcode to generate the source for the entity, but you will have to regenerate the file(s) manually whenever you make changes to the object model. A good tip is to add customizations to the file named Entity+CoreDataClass.swift, that makes it easier whenever you need to regenerate the entity code.

import Foundation
import CoreData
import CoreDataCodable

@objc(Entity)
public class Entity: NSManagedObject {

}

extension Entity {

    enum CodingKeys: String, CodingKey {
        case name
        case url
    }

    public func setValues(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        name = try container.decode(String.self, forKey: .name)
        url = try container.decode(URL.self, forKey: .url)
    }

}