To Create Action That Accepts a Parameter Of Any Type Derived From The Parameter Type (Polymorphic Parameter)

Question

I want to build a dynamic structure for a client to ask server in web API. I have tried to use the following code to deal with my question, however, it isn't working.

1. How can I send a generic type like <travel> to service
2. How can I change server code (or all need to change client/server)?

PS:Thank you for your patience if you have read my question to the end.

Client Code

var serializer = new JavaScriptSerializer();    
var product = new travel() { travel_desc = "select * from travel" };    
var jsonText = serializer.Serialize(product);    
var client = new HttpClient();    
client.BaseAddress = new Uri("http://localhost:65370/");     
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));    
StringContent content = new StringContent(jsonText, Encoding.UTF8, "application/json");     

var z = client.PostAsync<travel>("api/bb", product, new JsonMediaTypeFormatter()).Result;

Server Code, which is not working

public IHttpActionResult Post< T > (Object x) where T : new()    
{    
                ........................    
}

by the way it is okay but i don't know how to send < T > to server

public IHttpActionResult Post(Object x)    
{    
                ........................    
}     

Error message
Client call server, server will be getting an error message " StatusCode: 404, ReasonPhrase: 'Not Found' "

 var z = client.PostAsync < travel > ("api/dd", product, new JsonMediaTypeFormatter()).Result; <--client

    public class ddController< T > : ApiController {public virtual void Post() {   ... }  } <---server    





  // sorry all , my English isn't very well , so I will try to use code to tell everyone how i want 
// in format situations,I will create 2 controller when I have 2 models(ex: users/product) , as following (client)
                var a = client.PostAsync("api/users", users, new JsonMediaTypeFormatter()).Result;
                var b = client.PostAsync("api/product", product, new JsonMediaTypeFormatter()).Result;

//and then when the users and product controllers was created the post code should be like as following (server)
                public IHttpActionResult Postusers(users travel) {}
                public IHttpActionResult Postproduct(product travel) {}

   //now i just want to create 1 controller for above  like as follwing 
                 var b = client.PostAsync<users/product>("api/all", product, new JsonMediaTypeFormatter()).Result;(client)

                 public IHttpActionResult Post<T>(Object ForAll) where T : new() {} (server)

Answer 1

JSON.NET, the Web API JSON serializer, is able to send type information when serializing an object, and use that same information to deserialize it.

The trick that it uses is including a $type property as the first property of the JSON object.

If you want to use this technique, you need to have a base class or an interface, for example ITravel, inherit all the possible classes from it, and use the base class or interface as the parameter type, like so:

public interface ITravel
{
  public int TravelId { get; set; }
}

public class TravelTypeA : ITravel
{
  public int TravelId { get; set; }
  public string Destination { get; set; }
}

public class TravelTypeB : ITravel
{
  ...
}

[HttpPost]
public object PostMeATravel(ITravel travel)
{
    // check what type is travel with "is" or ".GetType()"
}

You also need to instruct JSON to include type information when (de)serializing ITravel objects. (JSON TypeName Handling):

JsonSerializerSettings serializerSettings 
  = GlobalConfiguration.Configuration.Formatters
    .JsonFormatter.SerializerSettings;

serializerSettings.TypeNameHandling = TypeNameHandling.Auto;

And then you have to post a JSON with typeInformation, like this:

{
  $type: 'SampleApp.TravelTypeA, SampleApp',
  TravelId: 22,
  Destination: 'La Almunia de Doña Godina'
}

When you do so, JSON.NET will use the type information to create a TravelTypeA object, and pass it as parameter to the action, which expects an ITravel. Inside the action you can check the type of the received parameter if you need to do so, like this: if (travel.GetType().Name == "TravelTypeA") { ... }

Look at this Q&A for more information on how to do that, how it works, and advantages and drawbacks of this method and an alternative way of doing it: Deserialising Json to derived types in Asp.Net Web API

NOTE: you can use the excellent Postman complement for Chrome to test the Web API methods