ClientError

ClientError.cs

using Newtonsoft.Json;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Web.Http;

namespace DocSol.Webservice.Controllers
{
	public class ClientError : HttpResponseException
	{
		public ClientError(HttpStatusCode statusCode, object response)
			: base(new HttpResponseMessage(statusCode)
			{
				Content = GetJsonContent(response)
			})
		{}

		static StringContent GetJsonContent(object message)
		{
			return new StringContent(JsonConvert.SerializeObject(message), Encoding.UTF8, "application/json");
		}
	}
}

DogsController.cs

public class DogsController : ApiController
{
	public int Post(Dog dog)
	{
		if (dog == null) throw new ClientError(HttpStatusCode.BadRequest, "No dog provided to create");
		
		...
	}
}

OldWay.cs

public class DogsController : ApiController
{
	public int Post(Dog dog)
	{
		if (dog == null) 			
			throw new HttpResponseException(
					Request.CreateResponse(HttpStatusCode.BadRequest, new { Message = "No dog provided to create" })
					);
		
		...
	}
}