Using Codable on a dynamic type/object

Question

Hi I have the following structure nested in a bigger structure that is returned from an api call but I can't manage to encode/decode this part. The problem I am having is that the customKey and customValue are both dynamic.

{
    "current" : "a value"
    "hash" : "some value"
    "values": {
        "customkey": "customValue",
        "customKey": "customValue"
    }
}

I tried something like var values: [String:String] But that is obviously not working because its not actually an array of [String:String].

@vadian I don't see how this is duplicate of any of those questions. I modified the question to be more clear now. — Reshad
– Reshad, Commented Oct 13, 2017 at 9:34
I understand and reopened the question: Short answer: You cannot use Codable with dynamic keys. — vadian
– vadian, Commented Oct 13, 2017 at 9:36
If the keys are dynamic you can only use a dynamic collection type, in this case a dictionary. — vadian
– vadian, Commented Oct 13, 2017 at 10:28

Code Different · Accepted Answer · 2017-10-16 16:42:46Z

14

Since you linked to my answer to another question, I will expand that one to answer yours.

Truth is, all keys are known at runtime if you know where to look:

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 current: String
    var hash: String
    var values: [String: String]

    private enum CodingKeys: String, CodingKey {
        case current
        case hash
        case values
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        current = try container.decode(String.self, forKey: .current)
        hash = try container.decode(String.self, forKey: .hash)

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

Usage:

let jsonData = """
{
    "current": "a value",
    "hash": "a value",
    "values": {
        "key1": "customValue",
        "key2": "customValue"
    }
}
""".data(using: .utf8)!

let model = try JSONDecoder().decode(MyModel.self, from: jsonData)

edited Oct 16, 2017 at 16:42

answered Oct 15, 2017 at 22:28

Code Different

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6 Comments

Reshad Over a year ago

Thank you so much for your quick response. How would this apply if I have others keys in the JSON next to values that are normal decodable, Do I add a normal enum container for that ?

Code Different Over a year ago

I'm getting confused with your new requirements. Can you edit the JSON to show an example of it?

Reshad Over a year ago

I edited the JSON. What I meant was that the actual object that I am encoding and decoding has more than only values key->object. :)

TmSmth Over a year ago

@CodeDifferent I'm in a similar situation but in my case, i know "key1" and "key2" but not "values", i didn't figure out how to adapt your code, could you help ? thanks !

Code Different Over a year ago

@TmSmth there’s not enough info for me to help here. Please post a new question with the details of your specific situation

|

Michal S · Accepted Answer · 2018-06-17 01:11:18Z

1

Simplified answer, it is working with dictionary [String: String] (instatead of String you can use other struct):

let jsonData = """
{
    "current": "a value",
    "hash": "a value",
    "values": {
        "key1": "customValue",
        "key2": "customValue"
    }
}
""".data(using: .utf8)!

struct MyModel: Decodable {
    var current: String
    var hash: String
    var values: [String: String]
}

let model = try JSONDecoder().decode(MyModel.self, from: jsonData)

for (key,value) in model.values {
    print("key: \(key) value: \(value)")
}

answered Jun 17, 2018 at 1:11

Michal S

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