Swift4 / JSON / Decode - swift

Question

I'm new to Swift 4 and I looked for hours of hours to find a solution for my issue.
import Foundation
public struct Coin: Codable {
let name: String //= "Default"
let symbol: String
}
open class CoinCapIOAPI {
func fetchMap() {
let urlString = "http://socket.coincap.io/map"
guard let url = URL(string: urlString) else { return }
URLSession.shared.dataTask(with: url) { (data, response, error) in
// Maybe later...
guard let data = data else { return }
do {
let coins = try JSONDecoder().decode([Coin].self, from: data)
print(coins)
} catch let jsonErr {
print("Error: ", jsonErr)
}
}.resume()
}
}
The JSON looks like:
[
{ aliases: [ ],
name: "300 Token",
symbol: "300",
},
{
aliases: [ ],
name: "SixEleven",
symbol: "611",
},
]
I need just name and symbol. But without the default of name in the struct I get following error:
Error: keyNotFound(CoinBartender.Coin.(CodingKeys in _7C60C6A5E9E301137DE95AF645AB94EB).name, Swift.DecodingError.Context(codingPath: [Foundation.(_JSONKey in _12768CA107A31EF2DCE034FD75B541C9)(stringValue: "Index 91", intValue: Optional(91))], debugDescription: "No value associated with key name (\"name\").", underlyingError: nil))
If I add the default value for "name" I get this result:
[CoinBartender.Coin(name: "Default", symbol: "300"), CoinBartender.Coin(name: "Default", symbol: "611"),
Why does symbol work but name doesn't?

Answer 1

Please read the error message carefully. It's exactly describing the issue:
Error: keyNotFound(CoinBartender.Coin.(CodingKeys in _7C60C6A5E9E301137DE95AF645AB94EB).name, Swift.DecodingError.Context(codingPath: [Foundation.(_JSONKey in _12768CA107A31EF2DCE034FD75B541C9)(stringValue: "Index 91", intValue: Optional(91))], debugDescription: "No value associated with key name (\"name\").", underlyingError: nil))
It says that the 92nd entry (index is zero-based) does not have a key name
{"aliases":[],"symbol":"QTM"}
One solution is to declare name as optional
let name: String?

Answer 2

Your Coin struct should be like this:
public struct Coin: Codable {
let name: String? //= "Default"
let symbol: String
}
Because some indexes does not contain name.