Introduction to Web API

In this article we are going to focus on what is ASP.NET Web API and how to use it. The Prerequisites to learn Web API.

What is ASP.NET Web API
It is a framework for creating web API s on top of .NET Framework. It makes creating HTTP service simple and easy and supports wide range of devices.

Why Web APIs
1.Using Web API, We can not only expose data but also create our own services
2. We can use it for a wide range of clients may be a Browser application or a Mobile Device or any Desktop applications.
3. Makes sending/receiving data over HTTP to a wide range of devices very easy.
4. The client can be a service from other language like ruby or python any xaml application or a JS client.
5.Supports data formats such as JSON / XML and allows clients to provide the required response data format. Provision to provide our own data formatting using MediaTypeFormatters.
6.Simple and clean urls to understand such as : http://dotnetspider.com/session/webapi
7.Since it is based on http protocol it also supports caching.
8.Easy to consume from Javascript.
9.It can be hosted in IIS or any exe file or asp.net or unit test project.
10. It uses routing similar to ASP.NET MVC.

Basic components of Web API
1.Controller:
It is the heart of the Web API application.
It exposes the actions or the resources that can be consumed by the client.
2.Handlers:
IT allows us to keep track of the incoming request or the outgoing response
Facilitate Authentication.
3.Filters:
To provide additional functionality on top of the basic functionality.

Installation Instructions:
It is already included with ASP.NET MVC 4.
Visual Studio 2010
Download and install sp1 for Visual Studio 2010.
Download and install MVC 4 Project from Microsoft site here
http://www.microsoft.com/en-ca/download/details.aspx?id=30683
Visual Studio 2012
Already Built into it.

Prerequisites
Good to have knowledge in MVC architecture but not mandatory.
Good to have knowledge in WCF data services but not mandatory.
C# knowledge is required.
Knowledge in JSON/XML.

How to test Web API services
Fiddler is a great tool to test Web API services. It also provides the facility to tweak the request headers including the content format we expect from service.

Web API in action
Now we will see how to create a simple Web API application using Visual Studio 2012.

Here we will create a Web API that returns a list of students.
Step1: Launch Visual Studio 2012 -> File -> New -> Project -> On the Left Side of open dialog box Select Installed ->Templates -> Visual C# -> Web -> Then select ASP.NET MVC4 Web Application. Name it as "MyFirstWebAPIApp".
Step2: In the New ASP.NET MVC 4 Project window select Empty as shown below and click on ok:

Step3: Right click Models Folder and Add new class "Student".

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace MyFirstWebAPIApp.Models
{
    public class Student
    {
        public Student(){}
        public Student(int id,string name,DateTime joiningDate,string cls)
        {
            this.StudentId = id;
            this.StudentName = name;
            this.JoiningDate = joiningDate;
            this.Class = cls;
        }
        public int StudentId { get; set; }
        public string StudentName { get; set; }
        public DateTime JoiningDate { get; set; }
        public string Class { get; set; }
    }
}

namespace MyFirstWebAPIApp.Controllers
{
    public class StudentController : ApiController  
    {
        public List Get()
        {
            List lst = new List();
            lst.Add(new Student(1, "john", new DateTime(2014, 1, 1), "B.Tech I year"));
            lst.Add(new Student(1, "robert", new DateTime(2014, 2, 1), "B.Tech I year"));
            lst.Add(new Student(1, "tina", new DateTime(2014, 1, 4), "B.Tech I year"));
            return lst;
        }

    }
}