Codable object mapping array element to string

Question

I have a (annoying) situation where my back-end returns an object like this:

{
"user": {
        "name": [
            "John"
        ],
        "familyName": [
            "Johnson"
        ]
    }
}

where each property is an array that holds a string as its first element. In my data model struct I could declare each property as an array but that really would be ugly. I would like to have my model as such:

struct User: Codable {
    var user: String
    var familyName: String
}

But this of course would fail the encoding/decoding as the types don't match. Until now I've used ObjectMapper library which provided a Map object and currentValue property, with that I could declare my properties as String type and in my model init method assig each value through this function:

extension Map {
    public func firstFromArray<T>(key: String) -> T? {
        if let array = self[key].currentValue as? [T] {
            return array.first
        }
        return self[key].currentValue as? T
    }
}

But now that I am converting to Codable approach, I don't know how to do such mapping. Any ideas?

Puneet Sharma · Accepted Answer · 2017-11-21 17:50:57Z

2

You can override init(from decoder: Decoder):

let json = """
{
    "user": {
        "name": [
        "John"
        ],
        "familyName": [
        "Johnson"
        ]
    }
}
"""

struct User: Codable {
    var name: String
    var familyName: String

    init(from decoder: Decoder) throws {
        let container:KeyedDecodingContainer = try decoder.container(keyedBy: CodingKeys.self)
        let nameArray = try container.decode([String].self, forKey: .name)
        let familyNameArray = try container.decode([String].self, forKey: .familyName)
        self.name = nameArray.first!
        self.familyName = familyNameArray.first!
    }

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

let data = json.data(using: .utf8)!
let decodedDictionary = try JSONDecoder().decode(Dictionary<String, User>.self, from: data)
print(decodedDictionary) // ["user": __lldb_expr_48.User(name: "John", familyName: "Johnson")]

let encodedData = try JSONEncoder().encode(decodedDictionary["user"]!)
let encodedStr = String(data: encodedData, encoding: .utf8)
print(encodedStr!) // {"name":"John","familyName":"Johnson"}

answered Nov 21, 2017 at 17:50

Puneet Sharma

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1 Comment

Au Ris Over a year ago

Thanks for a good answer. I decided to go with the computed property way though.

GetSwifty · Accepted Answer · 2017-11-21 18:12:10Z

1

My tendency would be to adapt your model to the data coming in and create computed properties for use in the application, e.g.

struct User: Codable {
    var user: [String]
    var familyName: [String]

    var userFirstName: String? {
        return user.first
    }

    var userFamilyName: String? {
        return familyName.first
    }
}

This allows you to easily maintain parody with the data structure coming in without the maintenance cost of overriding the coding/decoding.

If it goes well with your design, you could also have a UI wrapper Type or ViewModel to more clearly differentiate the underlying Model from it's display.

answered Nov 21, 2017 at 18:12

GetSwifty

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1 Comment

Au Ris Over a year ago

Thanks. I like this one better than overriding init.

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