Swift's JSONDecoder with multiple date formats in a JSON string?

Question

Swift\'s JSONDecoder offers a dateDecodingStrategy property, which allows us to define how to interpret incoming date strings in accordance with a

Answer 1

It is a little verbose, but more flexible approach: wrap date with another Date class, and implement custom serialize methods for it. For example:

let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"

class MyCustomDate: Codable {
    var date: Date

    required init?(_ date: Date?) {
        if let date = date {
            self.date = date
        } else {
            return nil
        }
    }

    public func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        let string = dateFormatter.string(from: date)
        try container.encode(string)
    }

    required public init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let raw = try container.decode(String.self)
        if let date = dateFormatter.date(from: raw) {
            self.date = date
        } else {
            throw DecodingError.dataCorruptedError(in: container, debugDescription: "Cannot parse date")
        }
    }
}

So now you are independent of .dateDecodingStrategy and .dateEncodingStrategy and your MyCustomDate dates will parsed with specified format. Use it in class:

class User: Codable {
    var dob: MyCustomDate
}

Instantiate with

user.dob = MyCustomDate(date)