ASP.Net Web API model binding not working like it

Question

I was under the impression that model binding in the ASP.Net Web API was supposed to support binding with the same minimum level of functionality supported by MVC.

Take the following controller:

public class WordsController : ApiController
{
    private string[] _words = new [] { "apple", "ball", "cat", "dog" };

    public IEnumerable<string> Get(SearchModel searchSearchModel)
    {
        return _words
            .Where(w => w.Contains(searchSearchModel.Search))
            .Take(searchSearchModel.Max);
    }
}

public class SearchModel
{
    public string Search { get; set; }
    public int Max { get; set; }
}

I'm requesting it with:

http://localhost:62855/api/words?search=a&max=2

Unfortunately the model does not bind as it would in MVC. Why is this not binding as I would expect? I'm going to have a lot of different model types in my application. It would be nice if binding just worked, like it does in MVC.

Answer 1

I have found the entire Web API 2 to be a difficult learning curve with lots of "Gotchas" I have read a few of the key books that cover many arcane nuances of this rich product offering. But basically, I thought there must be some core functionality that could take advantage of the best of the features. So, I set out to do four straight forward tasks. 1. Accept a query string, from a browser, into an Api2 Client and populate a simple .NET model. 2. Have the Client submit an async Post to an Api2 Server encoded in JSON extracted from the prior Model 3. Have the Server do a trivial conversion on the Post Request from the Client. 4. Pass it all back up to the Browser. This is it.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using System.Threading.Tasks;
using Newtonsoft.Json;

namespace Combined.Controllers  // This is an ASP.NET Web Api 2 Story
{
    //  Paste the following string in your browser -- the goal is to convert the last name to lower case 
    //  The return the result to the browser--You cant click on this one. This is all Model based. No Primitives.
    //  It is on the Local IIS--not IIS Express. This can be set in Project->Properties=>Web http://localhost/Combined with a "Create Virtual Directory"
    //  http://localhost/Combined/api/Combined?FirstName=JIM&LastName=LENNANE  // Paste this in your browser After the Default Page it displayed
    //
    public class CombinedController : ApiController
    {
        // GET: api/Combined   This handels a simple Query String request from a Browser
        // What is important here is that populating the model is from the URI values NOT the body which is hidden
        public Task<HttpResponseMessage> Get([FromUri]FromBrowserModel fromBrowser)
        {
            //
            //  The Client looks at the query string pairs from the Browser
            //  Then gets them ready to send to the server
            //
            RequestToServerModel requestToServerModel = new RequestToServerModel();
            requestToServerModel.FirstName = fromBrowser.FirstName;
            requestToServerModel.LastName = fromBrowser.LastName;
            //  Now the Client send the Request to the Server async and everyone awaits the Response
            Task<HttpResponseMessage> response = PostAsyncToApi2Server("http://localhost/Combined/api/Combined", requestToServerModel );
            return response;    // The response from the Server should be sent back to the Browser from here.
        }
        async Task<HttpResponseMessage> PostAsyncToApi2Server(string uri, RequestToServerModel requestToServerModel)
        {
            using (var client = new HttpClient())
            {
                //  Here the Method waits for the Request to the Server to complete
                return await client.PostAsJsonAsync(uri, requestToServerModel)
                    .ContinueWith((postTask) => postTask.Result.EnsureSuccessStatusCode());
            }
        }
        //  POST: api/Combined    This Handles the Inbound Post Request from the Client
        //  NOTICE THE [FromBody] Annotation. This is the key to extraction the model from the Body of the Post Request-- not the Uri ae in [FromUri]
        //  Also notice that there are no Async methods here. Not required, async would probably work also.
        //
        public HttpResponseMessage Post([FromBody]RequestToServerModel fromClient)
        {
            //
            //  Respond to an HttpClient request Synchronously
            //  The model is serialised into Json by specifying the Formatter Configuration.Formatters.JsonFormatter
            //  Prep the outbound response
            ResponseToClientModel responseToClient = new ResponseToClientModel();
            //
            //  The conversion to lower case is done here using the Request Body Data Model
            //            
            responseToClient.FirstName = fromClient.FirstName.ToLower();
            responseToClient.LastName = fromClient.LastName.ToLower();
            //
            //  The Client should be waiting patiently for this result
            //
            using (HttpResponseMessage response = new HttpResponseMessage())
            {
                return this.Request.CreateResponse(HttpStatusCode.Created, responseToClient, Configuration.Formatters.JsonFormatter);    // Respond only with the Status and the Model
            }
        }
        public class FromBrowserModel
        {
            public string FirstName { get; set; }
            public string LastName { get; set; }
        }
        public class RequestToServerModel
        {
            public string FirstName { get; set; }
            public string LastName { get; set; }
        }

        public class ResponseToClientModel
        {
            public string FirstName { get; set; }
            public string LastName { get; set; }
        }

        
    }
}

Answer 2

Take a look at this: How WebAPI does Parameter Binding

You need to decorate your complex parameter like so:

public IEnumerable<string> Get([FromUri] SearchModel searchSearchModel)

OR

public IEnumerable<string> Get([ModelBinder] SearchModel searchSearchModel)