Codable, Decodable only a value out of Dictionary - swift4

Question

I have a json response of an API. This returns a also value, which is a Dictionary. How to can I achieve to store / map only the value of this Dictionary. Here is an example which can be simply put into a playground:
id = ["$oid": "591ae6cb9d1fa2b6e47edc33"]
should only be
id = "591ae6cb9d1fa2b6e47edc33"
Here is an example which can be simply put into a playground:
import Foundation
struct Location : Decodable {
enum CodingKeys : String, CodingKey {
case id = "_id"
}
var id : [String:String]? // this should be only a string with the value of "$oid"
}
extension Location {
public init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
id = try values.decode([String:String]?.self, forKey: .id)
}
}
var json = """
[
{
"_id": {
"$oid": "591ae6cb9d1fa2b6e47edc33"
}
},
{
"_id": {
"$oid": "591ae6cd9d1fa2b6e47edc34"
}
}
]
""".replacingOccurrences(of: "}\n{", with: "}\\n{").data(using: .utf8)!
let decoder = JSONDecoder()
do {
let locations = try decoder.decode([Location].self, from: json)
locations.forEach { print($0) }
} catch {
print(error.localizedDescription )
}

Answer 1

You were almost there:
struct Location {
var id: String
}
extension Location: Decodable {
private enum CodingKeys: String, CodingKey {
case id = "_id"
}
public init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
let _id = try values.decode([String: String].self, forKey: .id)
id = _id["$oid"]!
}
}
If you have mote keys under _id in the JSON data, I'd strongly suggest you make a private struct that represents the struct for the benefit of type safety.