Dynamic dictionary naming decoder json

Question

Swift 4. I have a very similar situation than Using Codable for a dynamic type / object , but for me a variable is the name of the dictionary and not inside. It looks like this:

{
    "customName": {
        "constantKey": Double,
        "constantKey2": Double,
    }
}

Here is the code I am trying to modify, it was suggested as an answer for another question, and I made small changes:

 struct GenericCodingKeys: CodingKey {
    var intValue: Int?
    var stringValue: String

    init?(intValue: Int) { self.intValue = intValue; self.stringValue = "\(intValue)" }
    init?(stringValue: String) { self.stringValue = stringValue }

    static func makeKey(name: String) -> GenericCodingKeys {
        return GenericCodingKeys(stringValue: name)!
    }
}


struct MyModel: Decodable {
    var customName: [String: Double]

    private enum CodingKeys: String, CodingKey {
        case customName
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)

    customName = [String: String]()
    let subContainer = try container.nestedContainer(keyedBy: GenericCodingKeys.self, forKey: .customName)
    for key in subContainer.allKeys {
        customName[key.stringValue] = try subContainer.decode(Double.self, forKey: key)
        }
    }
}

And here is the obvious error I received as I don’t know how to change this user name: keyNotFound(Testapp.MyModel.(CodingKeys in _7A951077E4B6EF2E56D367C5DE0BF0AC).customName, Swift.DecodingError.Context(codingPath: [], debugDescription: "Cannot get KeyedDecodingContainer<GenericCodingKeys> -- no value found for key \"customName\"", underlyingError: nil))

Answer 1

If you already know all the keys in the internal JSON, use struct to use static typing. Assuming your JSON has only 1 key at the top level (your key customName):

struct MyModel: Decodable {
    struct InnerModel: Decodable {
        var constantKey1: Double
        var constantKey2: Double
    }

    var customName: InnerModel

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: GenericCodingKeys.self)

        // Assume that there only 1 key at the top level in the JSON
        if let key = container.allKeys.first {
            customName = try container.decode(InnerModel.self, forKey: key)
        } else {
            throw NSError(domain: NSCocoaErrorDomain, code: 0, userInfo: [NSLocalizedDescriptionKey: "JSON is empty"])
        }
    }
}