C# Newtonsoft.Json Custom Deserializer

Question

I'm working with an API that is returning results to me in a different way than I'm used to dealing with, and seemingly non-standard.

For example, here's a snippet of Customer data:

{
    "CustomerID": {
        "value": "EXAMPLE"
    },
    "CustomerCurrencyID": {
        "value": "USD"
    }
}

That "value" property seems very unnecessary, so I would like to see if I can just bypass that all together and deserialize that JSON into an object like so:

class Customer {
    public string CustomerID { get; set; }
    public string CustomerCurrencyID { get; set; }
}

I'm currently working on writing a custom JsonConverter to handle this, so if I'm heading down the right path just let me know, but any tips/tricks here would be much appreciated!

Answer 1

You can do this with a generic custom JsonConverter such as the following:

public class WrapWithValueConverter<TValue> : JsonConverter
{
    // Here we take advantage of the fact that a converter applied to a property has highest precedence to avoid an infinite recursion.
    class DTO { [JsonConverter(typeof(NoConverter))] public TValue value { get; set; } public object GetValue() => value; }

    public override bool CanConvert(Type objectType) => typeof(TValue).IsAssignableFrom(objectType);
    
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        => serializer.Serialize(writer, new DTO { value = (TValue)value });

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        => serializer.Deserialize<DTO>(reader)?.GetValue();
}

public class NoConverter : JsonConverter
{
    // NoConverter taken from this answer https://stackoverflow.com/a/39739105/3744182
    // By https://stackoverflow.com/users/3744182/dbc
    // To https://stackoverflow.com/questions/39738714/selectively-use-default-json-converter
    public override bool CanConvert(Type objectType)  { throw new NotImplementedException(); /* This converter should only be applied via attributes */ }
    public override bool CanRead => false;
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) => throw new NotImplementedException();
    public override bool CanWrite => false;
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) => throw new NotImplementedException();
}

Then you can apply it to your model as follows:

class Customer {
    [JsonConverter(typeof(WrapWithValueConverter<string>))]
    public string CustomerID { get; set; }
    [JsonConverter(typeof(WrapWithValueConverter<string>))]
    public string CustomerCurrencyID { get; set; }
}

Demo fiddle #1 here.

Or, if you want all strings to be wrapped in a {"value": <string value>} object, you can add the converter to JsonSerializerSettings.Converters when serializing and deserializing:

var settings = new JsonSerializerSettings
{
    Converters = { new WrapWithValueConverter<string>() },
};

var model = JsonConvert.DeserializeObject<Customer>(json, settings);

var json2 = JsonConvert.SerializeObject(model, Formatting.Indented, settings);

Demo fiddle #2 here.

If your value is an enum and you want to serialize it as a string, you can replace NoConverter with StringEnumConverter by using the following:

public class WrapEnumWithValueConverter<TEnum> : JsonConverter where TEnum: Enum
{
    // Here we take advantage of the fact that a converter applied to a property has highest precedence to avoid an infinite recursion.
    class DTO { [JsonConverter(typeof(StringEnumConverter))] public TEnum value { get; set; } public object GetValue() => value; }

    public override bool CanConvert(Type objectType) => typeof(TEnum).IsAssignableFrom(objectType);

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        => serializer.Serialize(writer, new DTO { value = (TEnum)value });

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        => serializer.Deserialize<DTO>(reader)?.GetValue();
}

Demo fiddle #3 here.