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Get Started with ASP.NET Web API 2 (C#)

  • Artikel

by Mike Wasson

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In this tutorial, you will use ASP.NET Web API to create a web API that returns a list of products.

HTTP is not just for serving up web pages. HTTP is also a powerful platform for building APIs that expose services and data. HTTP is simple, flexible, and ubiquitous. Almost any platform that you can think of has an HTTP library, so HTTP services can reach a broad range of clients, including browsers, mobile devices, and traditional desktop applications.

ASP.NET Web API is a framework for building web APIs on top of the .NET Framework.

Software versions used in the tutorial

See Create a web API with ASP.NET Core and Visual Studio for Windows for a newer version of this tutorial.

Create a Web API Project

In this tutorial, you will use ASP.NET Web API to create a web API that returns a list of products. The front-end web page uses jQuery to display the results.

Screenshot of the local host browser window, showing the sample project with a list of products, their prices, and a search by I D field and button.

Start Visual Studio and select New Project from the Start page. Or, from the File menu, select New and then Project.

In the Templates pane, select Installed Templates and expand the Visual C# node. Under Visual C#, select Web. In the list of project templates, select ASP.NET Web Application. Name the project "ProductsApp" and click OK.

Screenshot of the 'add new project' template options, highlighting the steps and selections for creating the new project.

In the New ASP.NET Project dialog, select the Empty template. Under "Add folders and core references for", check Web API. Click OK.

Screenshot of the new project dialog box, with different template options and three selections for folders and core reference.

Note

You can also create a Web API project using the "Web API" template. The Web API template uses ASP.NET MVC to provide API help pages. I'm using the Empty template for this tutorial because I want to show Web API without MVC. In general, you don't need to know ASP.NET MVC to use Web API.

Adding a Model

A model is an object that represents the data in your application. ASP.NET Web API can automatically serialize your model to JSON, XML, or some other format, and then write the serialized data into the body of the HTTP response message. As long as a client can read the serialization format, it can deserialize the object. Most clients can parse either XML or JSON. Moreover, the client can indicate which format it wants by setting the Accept header in the HTTP request message.

Let's start by creating a simple model that represents a product.

If Solution Explorer is not already visible, click the View menu and select Solution Explorer. In Solution Explorer, right-click the Models folder. From the context menu, select Add then select Class.

Screenshot of the solution explorer menu, displaying the options located in the models folder showing how to add a class.

Name the class "Product". Add the following properties to the Product class.

namespace ProductsApp.Models
{
    public class Product
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Category { get; set; }
        public decimal Price { get; set; }
    }
}

Adding a Controller

In Web API, a controller is an object that handles HTTP requests. We'll add a controller that can return either a list of products or a single product specified by ID.

Note

If you have used ASP.NET MVC, you are already familiar with controllers. Web API controllers are similar to MVC controllers, but inherit the ApiController class instead of the Controller class.

In Solution Explorer, right-click the Controllers folder. Select Add and then select Controller.

Screenshot of the solution explorer menu, displaying visual guidance for adding a controller class to the project.

In the Add Scaffold dialog, select Web API Controller - Empty. Click Add.

Screenshot showing the 'add scaffold' dialog box's menu options, highlighting the Web A P I controller - empty option.

In the Add Controller dialog, name the controller "ProductsController". Click Add.

Screenshot of the 'add controller' dialog box, shoing the word 'products controller' in the field box, and the add button under it.

The scaffolding creates a file named ProductsController.cs in the Controllers folder.

Screenshot of the solution explorer menu options, circling the newly created option called 'products controller dot C S in the controllers folder.

Note

You don't need to put your controllers into a folder named Controllers. The folder name is just a convenient way to organize your source files.

If this file is not open already, double-click the file to open it. Replace the code in this file with the following:

using ProductsApp.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Web.Http;

namespace ProductsApp.Controllers
{
    public class ProductsController : ApiController
    {
        Product[] products = new Product[] 
        { 
            new Product { Id = 1, Name = "Tomato Soup", Category = "Groceries", Price = 1 }, 
            new Product { Id = 2, Name = "Yo-yo", Category = "Toys", Price = 3.75M }, 
            new Product { Id = 3, Name = "Hammer", Category = "Hardware", Price = 16.99M } 
        };

        public IEnumerable<Product> GetAllProducts()
        {
            return products;
        }

        public IHttpActionResult GetProduct(int id)
        {
            var product = products.FirstOrDefault((p) => p.Id == id);
            if (product == null)
            {
                return NotFound();
            }
            return Ok(product);
        }
    }
}

To keep the example simple, products are stored in a fixed array inside the controller class. Of course, in a real application, you would query a database or use some other external data source.

The controller defines two methods that return products:

  • The GetAllProducts method returns the entire list of products as an IEnumerable<Product> type.
  • The GetProduct method looks up a single product by its ID.

That's it! You have a working web API. Each method on the controller corresponds to one or more URIs:

Controller Method URI
GetAllProducts /api/products
GetProduct /api/products/id

For the GetProduct method, the id in the URI is a placeholder. For example, to get the product with ID of 5, the URI is api/products/5.

For more information about how Web API routes HTTP requests to controller methods, see Routing in ASP.NET Web API.

Calling the Web API with Javascript and jQuery

In this section, we'll add an HTML page that uses AJAX to call the web API. We'll use jQuery to make the AJAX calls and also to update the page with the results.

In Solution Explorer, right-click the project and select Add, then select New Item.

Screenshot of teh solution explorer menu, highlighting the products app option to show its menu selections to add a new item.

In the Add New Item dialog, select the Web node under Visual C#, and then select the HTML Page item. Name the page "index.html".

Screenshot of the 'add new item' menu options, showing the web selection and the options available within it.

Replace everything in this file with the following:

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title>Product App</title>
</head>
<body>

  <div>
    <h2>All Products</h2>
    <ul id="products" />
  </div>
  <div>
    <h2>Search by ID</h2>
    <input type="text" id="prodId" size="5" />
    <input type="button" value="Search" onclick="find();" />
    <p id="product" />
  </div>

  <script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-2.0.3.min.js"></script>
  <script>
    var uri = 'api/products';

    $(document).ready(function () {
      // Send an AJAX request
      $.getJSON(uri)
          .done(function (data) {
            // On success, 'data' contains a list of products.
            $.each(data, function (key, item) {
              // Add a list item for the product.
              $('<li>', { text: formatItem(item) }).appendTo($('#products'));
            });
          });
    });

    function formatItem(item) {
      return item.Name + ': $' + item.Price;
    }

    function find() {
      var id = $('#prodId').val();
      $.getJSON(uri + '/' + id)
          .done(function (data) {
            $('#product').text(formatItem(data));
          })
          .fail(function (jqXHR, textStatus, err) {
            $('#product').text('Error: ' + err);
          });
    }
  </script>
</body>
</html>

There are several ways to get jQuery. In this example, I used the Microsoft Ajax CDN. You can also download it from http://jquery.com/, and the ASP.NET "Web API" project template includes jQuery as well.

Getting a List of Products

To get a list of products, send an HTTP GET request to "/api/products".

The jQuery getJSON function sends an AJAX request. The response contains array of JSON objects. The done function specifies a callback that is called if the request succeeds. In the callback, we update the DOM with the product information.

$(document).ready(function () {
    // Send an AJAX request
    $.getJSON(apiUrl)
        .done(function (data) {
            // On success, 'data' contains a list of products.
            $.each(data, function (key, item) {
                // Add a list item for the product.
                $('<li>', { text: formatItem(item) }).appendTo($('#products'));
            });
        });
});

Getting a Product By ID

To get a product by ID, send an HTTP GET request to "/api/products/id", where id is the product ID.

function find() {
    var id = $('#prodId').val();
    $.getJSON(apiUrl + '/' + id)
        .done(function (data) {
            $('#product').text(formatItem(data));
        })
        .fail(function (jqXHR, textStatus, err) {
            $('#product').text('Error: ' + err);
        });
}

We still call getJSON to send the AJAX request, but this time we put the ID in the request URI. The response from this request is a JSON representation of a single product.

Running the Application

Press F5 to start debugging the application. The web page should look like the following:

Screenshot of the web browser, showing an all products bullet form, with their prices, followed by the 'search by I D' field under it.

To get a product by ID, enter the ID and click Search:

Screenshot of the browser, showing all products and prices, in bullet form, and the number 2 in the 'search by I D' field.

If you enter an invalid ID, the server returns an HTTP error:

Screenshot of the browser, listing all products and their prices, and showing the 'not found' error message under the 'search by I D' field.

Using F12 to View the HTTP Request and Response

When you are working with an HTTP service, it can be very useful to see the HTTP request and response messages. You can do this by using the F12 developer tools in Internet Explorer 9. From Internet Explorer 9, press F12 to open the tools. Click the Network tab and press Start Capturing. Now go back to the web page and press F5 to reload the web page. Internet Explorer will capture the HTTP traffic between the browser and the web server. The summary view shows all the network traffic for a page:

Screenshot of the H T T P request and response message window, showing a list of U R Ls, and all the network traffic responses.

Locate the entry for the relative URI "api/products/". Select this entry and click Go to detailed view. In the detail view, there are tabs to view the request and response headers and bodies. For example, if you click the Request headers tab, you can see that the client requested "application/json" in the Accept header.

Screenshot of the H T T P request and response message dialog, showing an example of an individual A P I request response.

If you click the Response body tab, you can see how the product list was serialized to JSON. Other browsers have similar functionality. Another useful tool is Fiddler, a web debugging proxy. You can use Fiddler to view your HTTP traffic, and also to compose HTTP requests, which gives you full control over the HTTP headers in the request.

See this App Running on Azure

Would you like to see the finished site running as a live web app? You can deploy a complete version of the app to your Azure account.

You need an Azure account to deploy this solution to Azure. If you do not already have an account, you have the following options:

Next Steps