Omit null values in json response from Nancy FX - json

Question

I am trying to create a REST service using Nancy FX in a C# environment. I can easily do a Response.AsJson and it all looks good. But I want the response to omit any properties that are null.
I have not been able to figure out how to do this yet.
Could someone point to me towards a help document or a blog post somewhere, that explains how to do this.
Thanks,
JP

Answer 1

I would create a dynamic anonymous type and return that. So let's say you have a User object like this:
public class User
{
public string Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
You want to pass back an instance of this type as a JSON response so you will have some code like this:
Get["/user/{userid}"] = parameters =>
{
var user = UserService.GetById(Db, (string)parameters.userid);
if (user == null) return HttpStatusCode.UnprocessableEntity;
return Response.AsJson(user);
};
But you don't want to return the User instance, instead you want to return an separate instance of a dynamic type that will only implement a property if the property value is not null for a given instance.
So I would suggest code something like this:
Get["/user/{userid}"] = parameters =>
{
var user = UserService.GetById(Db, (string)parameters.userid);
if (user == null) return HttpStatusCode.UnprocessableEntity;
dynamic userDTO = new ExpandoObject();
userDTO.Id = user.Id;
if (!string.IsNullOrEmpty(user.FirstName)) userDTO.FirstName = user.FirstName;
if (!string.IsNullOrEmpty(user.LastName)) userDTO.Lastname = user.LastName;
return Response.AsJson((ExpandoObject)userDTO);
};
Note 1
You don't need to test for the Id since that is implied by the successful return of the User instance from the database.
Note 2
You need to use a dynamic type so you can include ad hoc properties. The problem is that extension methods cannot accept dynamic types. To avoid this you need to declare it as an ExpandoObject but use it as a dynamic. This trick incurs a processing overhead but it allows you to cast the dynamic to an ExpandoObject when passing it in to the AsJson() extension method.