Writing a custom JsonConverter is another approach mentioned in similar questions. However, due to nature of how JsonConverter is designed, using that approach for this question is tricky, as you need to be careful with the WriteJson implementation to avoid getting into infinite recursion: JSON.Net throws StackOverflowException when using [JsonConvert()].
One possible implementation:
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
//JToken t = JToken.FromObject(value); // do not use this! leads to stack overflow
JsonObjectContract contract = (JsonObjectContract)serializer.ContractResolver.ResolveContract(value.GetType());
writer.WriteStartObject();
writer.WritePropertyName(value.GetType().Name);
writer.WriteStartObject();
foreach (var property in contract.Properties)
{
// this removes any property with null value
var propertyValue = property.ValueProvider.GetValue(value);
if (propertyValue == null) continue;
writer.WritePropertyName(property.PropertyName);
serializer.Serialize(writer, propertyValue);
//writer.WriteValue(JsonConvert.SerializeObject(property.ValueProvider.GetValue(value))); // this adds escaped quotes
}
writer.WriteEndObject();
writer.WriteEndObject();
}