PATCHSupportWebApi.cs

[AcceptVerbs("PATCH")]
public HttpResponseMessage PatchOrder(int id, Order updatedOrder)
{
    using (DBOrderEntities objContext = new DBOrderEntities()) {
      var order = objContext.Orders.SingleOrDefault(o => o.ID  == id);
      if (order == null)
      {
          throw new HttpResponseException(HttpStatusCode.NotFound);
      }
      //write code to update the given proerties here.
      objContext.SaveChanges();                
    }
    return Request.CreateResponse(HttpStatusCode.NoContent);
}

The first version shows how to handle the PATCH request using the AcceptVerbsAttribute. But there is still a lot of potential code to write to determine exactly which properties of the updatedOrder were sent with the request.