Multiple coding keys for a single data in Codable

Question

The API I am using supports multi-language. For instance:

// For Japanese
{
    "earthquake_detail": {
        "advisory_title_ja": "津波注意報",
        "depth_title_ja": "震源深さ",
        "depth_value_ja": "30km",
    }
}

// For English

{
    "earthquake_detail": {
        "advisory_title_en": "Tsunami Advisory",
        "depth_title_en": "Depth",
        "depth_value_en": "30km",       
    }
}

I am using swift codable to map them to a struct. Is there a way that I can map multiple coding keys to a single variable? Here is my swift struct.

struct EarthquakeDetail: Codable {
    var advisoryTitle, depthTitle, depthValue: String?

    enum CodingKeys: String, CodingKey {
        case advisoryTitle = "advisory_title_ja"
        case depthTitle = "depth_title_ja"
        case depthValue = "depth_value_ja"
    }
}

What I want to obtain is for Japanese this will be the coding keys:

enum CodingKeys: String, CodingKey {
            case advisoryTitle = "advisory_title_ja"
            case depthTitle = "depth_title_ja"
            case depthValue = "depth_value_ja"
        }

and for English:

enum CodingKeys: String, CodingKey {
            case advisoryTitle = "advisory_title_en"
            case depthTitle = "depth_title_en"
            case depthValue = "depth_value_en"
        }

vadian · Accepted Answer · 2020-03-26 05:55:42Z

If you are not going to use the convertFromSnakeCase strategy add a custom key decoding strategy which drops the _xx from the three coding keys.

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .custom { codingKeys in
    let lastKey = codingKeys.last!
    if lastKey.intValue != nil || codingKeys.count != 2 { return lastKey }
    if codingKeys.dropLast().last!.stringValue != "earthquake_detail" { return lastKey }
    return AnyCodingKey(stringValue: String(lastKey.stringValue.dropLast(3)))!
}

If the earthquake_detail key is deeper than on level 2 change != 2 accordingly

To be able to create custom coding keys you need

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

    init?(stringValue: String) { self.stringValue = stringValue }

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

Now declare EarthquakeDetail as follows

struct EarthquakeDetail: Codable {
    var advisoryTitle, depthTitle, depthValue: String

    enum CodingKeys: String, CodingKey {
        case advisoryTitle = "advisory_title"
        case depthTitle = "depth_title"
        case depthValue = "depth_value"
    }
}

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