How to encode Realm's List<> type - swift

Question

I am trying to encode my Realm database to JSON. Everything is working except the List<> encoding. So my question is, how would you encode List<>? Because the List doesn't conform to Encodable neighter Decodable protocol.
Right now I am doing this:
#objcMembers class User: Object, Codable{
dynamic var name: String = ""
let dogs = List<Dog>()
private enum UserCodingKeys: String, CodingKey {
case name
case dogs
}
convenience init(name: String) {
self.init()
self.name = name
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: UserCodingKeys.self)
try container.encode(name, forKey: .name)
}
#objcMembers class Dog: Object, Codable{
dynamic var name: String = ""
dynamic var user: User? = nil
private enum DogCodingKeys: String, CodingKey {
case name
}
convenience init(name: String) {
self.init()
name = name
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: DogCodingKeys.self)
try container.encode(name, forKey: .name)
}
}
and like this I am trying to do it:
var json: Any?
let user = RealmService.shared.getUsers()
var usersArray = [User]()
for user in users{
usersArray.append(user)
}
let jsonEncoder = JSONEncoder()
let jsonDecoder = JSONDecoder()
let encodedJson = try? jsonEncoder.encode(portfoliosArray)
if let data = encodedJson {
json = try? JSONSerialization.jsonObject(with: data, options: .allowFragments)
if let json = json {
print(String(describing: json))
}
}
So the question is how I am able to encode the List<Dog>?

Answer 1

To make a Realm object model class with a property of type List conform to Encodable, you can simply convert the List to an Array in the encode(to:) method, which can be encoded automatically.
extension User: Encodable {
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(self.username, forKey: .username)
let dogsArray = Array(self.dogs)
try container.encode(dogsArray, forKey: .dogs)
}
}
Test classes I used (slightly different from the ones in your question, but I already had these on hand and the methods in question will be almost identical regardless of the variable names):
class Dog: Object,Codable {
#objc dynamic var id:Int = 0
#objc dynamic var name:String = ""
}
class User: Object, Decodable {
#objc dynamic var id:Int = 0
#objc dynamic var username:String = ""
#objc dynamic var email:String = ""
let dogs = List<Dog>()
private enum CodingKeys: String, CodingKey {
case id, username, email, dogs
}
required convenience init(from decoder: Decoder) throws {
self.init()
let container = try decoder.container(keyedBy: CodingKeys.self)
id = try container.decode(Int.self, forKey: .id)
username = try container.decode(String.self, forKey: .username)
email = try container.decode(String.self, forKey: .email)
let dogsArray = try container.decode([Dog].self, forKey: .dogs)
dogs.append(objectsIn: dogsArray)
}
}
Test the encoding/decoding:
let userJSON = """
{
"id":1,
"username":"John",
"email":"example#ex.com",
"dogs":[
{"id":2,"name":"King"},
{"id":3,"name":"Kong"}
]
}
"""
do {
let decodedUser = try JSONDecoder().decode(User.self, from: userJSON.data(using: .utf8)!)
let encodedUser = try JSONEncoder().encode(decodedUser)
print(String(data: encodedUser, encoding: .utf8)!)
} catch {
print(error)
}
Output:
{"username":"John","dogs":[{"id":2,"name":"King"},{"id":3,"name":"Kong"}]}

Answer 2

You could resort to a mini-hack by making List conform to Encodable:
extension List: Encodable {
public func encode(to coder: Encoder) throws {
// by default List is not encodable, throw an exception
throw NSError(domain: "SomeDomain", code: -1, userInfo: nil)
}
}
// let's ask it to nicely encode when Element is Encodable
extension List where Element: Encodable {
public func encode(to coder: Encoder) throws {
var container = coder.unkeyedContainer()
try container.encode(contentsOf: self)
}
}
Two extensions are needed as you can't add protocol conformance and where clauses at the same time.
Also note that this approach doesn't provide compile-time checks - e.g. a List<Cat> will throw an exception an runtime if Cat is not encodable, instead of a nice compile time error.
The upside is lot of boilerplate code no longer needed:
#objcMembers class User: Object, Encodable {
dynamic var name: String = ""
let dogs = List<Dog>()
convenience init(name: String) {
self.init()
self.name = name
}
}
#objcMembers class Dog: Object, Encodable {
dynamic var name: String = ""
dynamic var user: User? = nil
convenience init(name: String) {
self.init()
name = name
}
}
This is also scalable, as adding new classes don't require any encoding code, but with the mentioned downside of not being fully type safe at compile time.