How to serialize an object to a JSON string property instead of an object using Json.Net

Question

I have the following class structure. What I am trying to achieve is instead of Bar serialized as an object in JSON, serialize as string with its inner property Name value and ignore the Id property. And I don't have a scenario where I need to deserialize it, but I have to load the Bar objects from database with other properties and do some internal manipulation but not use it for transport.

class Foo
{
    [JsonProperty("bar")]
    public Bar Bar { get; set; }
}

class Bar
{
    [JsonIgnore]
    public Guid Id { get; set; }
    [JsonProperty]
    public string Name { get; set; }
}

Expected JSON:

{
    bar: "test"
}

Answer 1

Use a custom JsonConverter and you can control your conversion to output whatever you want.

Something like:

    public class BarConverter : JsonConverter
    {

        public override bool CanConvert(Type objectType)
        {
            return objectType == typeof(Bar);
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            var bar = value as Bar;
            serializer.Serialize(writer, bar.Name);
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
              // Note: if you need to read to, you'll need to implement that here too
              // otherwise just throw a NotImplementException and override `CanRead` to return false
              throw new NotImplementedException();
        }
    }

Then you can either decorate your property or the Bar class (depending on whether you always want Bar serialized like this, or only for this property) with the JsonConverterAttribute:

[JsonConverter(typeof(BarConverter))]
public Bar Bar { get; set; }

Or:

[JsonConverter(typeof(BarConverter))]
public class Bar

Another "quick and dirty" way to do it is to just have a shadow property that will be serialized:

public class Foo
{
    [JsonProperty("bar")]         // this will be serialized as "bar"
    public string BarName 
    {
        get { return Bar.Name; }
    }

    [JsonIgnore]                  // this won't be serialized
    public Bar Bar { get; set; }
}

Note if you want to be able to read then you'd need to provide a setter too and figure out how to convert the string name back to an instance of Bar. That's where the quick and dirty solution gets a little unpleasant because you don't have a easy way to restrict setting BarName to just during deserialization.