How to custom deserialize into an object with json.net

Question

I used http://json2csharp.com/ to generate a csharp class that represents my JSON, which worked wonderfully. However, after working with the third party api for a while, I realized that their responses aren't always sending the same type of data. I'm querying their API for Ticket data, and each ticket has a SellPrice. Sometimes they return that SellPrice as a Money object that has a currency (string) and amount (double), and sometimes they send it back as just a double. So I'm trying to find a way to handle this gracefully, so that I always set the Amount of my SellPrice object. Here's a short version of the code that works when they send a Money object as SellPrice

public class Ticket
{
    public string Ticket_Id {get; set;}
    //... other fields
    public SellPrice SellPrice {get; set;}
}
public class SellPrice
{
    public string Currency {get; set;}
    public double Amount {get; set;}
}

And then when I get the Json, I deserialize like so, which works great...

for (int i = 0; i < jItems.Count; i++)
{
    TUTicket2 item = jItems[i].ToObject<TUTicket2>();
}

...until I run into an API call that returns a double instead of an object.

So just looking at the case where it's Money object, I thought I'd try to create a constructor so that I can set the values depending on the object type, like so:

public class SellPrice
{
    public SellPrice(object sellPrice)
    {
        if (sellPrice.GetType() == typeof(Dictionary<string, object>))
        {
            Currency = (string)((Dictionary<string, object>)sellPrice)["Currency"];
            Amount = (double)((Dictionary<string, object>)sellPrice)["Currency"];
        }
    }
    public string Currency { get; set; }
    public double Amount { get; set; }
}

But that doesn't work because the sellPrice object is always null, so I think I'm barking up the wrong tree there. Is there a way to do this easily? I think my problem is the way it auto-deserializes to an object type, but I've been looking through the code/documentation and haven't figured out what I'm missing.

I have a couple goals here: We are doing enough API work that I'd like to be able to utilize a tool like json2csharp to generate the classes. I'd also like to avoid doing manual deserialization for every class/object, although if that's my only option, I can go in that direction, it just feels like overkill when 99% of the values behave normally. I also don't want to end up with X different versions of each of my classes depending on which API call I make. I'm trying to find some solution that just lets me override a small portion instead of everything. Any feedback would be appreciated.

Brian Rogers · Accepted Answer · 2018-11-15 19:54:38Z

1

You can handle this by making a custom JsonConverter for your SellPrice class like this:

public class SellPriceConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(SellPrice);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JToken token = JToken.Load(reader);
        SellPrice sellPrice = new SellPrice();
        if (token.Type == JTokenType.Object)
        {
            serializer.Populate(token.CreateReader(), sellPrice);
        }
        else if (token.Type == JTokenType.Float)
        {
            sellPrice.Amount = (double)token;
            // if there is a default currency, set it here, e.g.:
            // sellPrice.Currency = "USD";
        }
        else
        {
            throw new JsonException("Unexpected token type for SellPrice: " + token.Type.ToString());
        }
        return sellPrice;
    }

    public override bool CanWrite
    {
        get { return false; }
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

To use it, all you would need to do is add a [JsonConverter] attribute to the SellPrice class like this:

[JsonConverter(typeof(SellPriceConverter))]
public class SellPrice 
{
    ...
}

Then you can just deserialize as normal and it should handle both situations.

Working demo here: https://dotnetfiddle.net/qZekyp

edited Nov 15, 2018 at 19:54

answered Nov 15, 2018 at 19:40

Brian Rogers

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1 Comment

Brendan Over a year ago

I was hoping there was something more simple, but I had a feeling this was the direction I would need to go. Thanks a lot for the concrete solution as well.

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