Getting Started with Web API Development in .NET

Welcome to the foundational guide for building robust and scalable web APIs using the .NET ecosystem. This section will walk you through the essential steps and concepts to get your first .NET Web API up and running.

What is a Web API?

A Web API (Application Programming Interface) is a set of rules and protocols that allows different software applications to communicate with each other over the internet. In the context of .NET, Web APIs are typically built using ASP.NET Core, a modern, cross-platform, high-performance framework for building web applications and services.

Prerequisites

Before you begin, ensure you have the following installed:

• .NET SDK: Download the latest version from the official .NET website.
• Code Editor: Visual Studio, Visual Studio Code, or Rider are highly recommended.

Creating Your First Web API Project

You can easily create a new Web API project using the .NET CLI or your preferred IDE.

Using the .NET CLI

Open your terminal or command prompt and run the following commands:

dotnet new webapi -n MyFirstWebApi
cd MyFirstWebApi
dotnet run
            

This will create a new project named MyFirstWebApi, navigate you into its directory, and start the development server. You should see output indicating that the server is running, typically on https://localhost:5001 or http://localhost:5000.

Using Visual Studio

1. Open Visual Studio.
2. Click "Create a new project".
3. Search for "ASP.NET Core Web API" and select the template.
4. Click "Next".
5. Enter your project name (e.g., MyFirstWebApi) and location, then click "Next".
6. Choose your desired .NET framework version and ensure "Enable OpenAPI support" is checked (this is useful for API documentation and testing).
7. Click "Create".
8. Once the project is created, you can run it by pressing F5 or clicking the "Run" button.

Understanding the Project Structure

A typical ASP.NET Core Web API project generated by the template includes several key files and folders:

• Controllers/: Contains your API controllers, which handle incoming HTTP requests.
• Properties/launchSettings.json: Configures application launch profiles, including ports and environment variables.
• appsettings.json: Stores application configuration settings.
• Program.cs: The entry point of your application, where the host is configured and started.
• MyFirstWebApi.csproj: The project file containing dependencies and metadata.

Your First API Endpoint

By default, the template usually includes a WeatherForecastController.cs. Let's examine it:

using Microsoft.AspNetCore.Mvc;

namespace MyFirstWebApi.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class WeatherForecastController : ControllerBase
    {
        private static readonly string[] Summaries = new[]
        {
            "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
        };

        private readonly ILogger<WeatherForecastController> _logger;

        public WeatherForecastController(ILogger<WeatherForecastController> logger)
        {
            _logger = logger;
        }

        [HttpGet]
        public IEnumerable<WeatherForecast> Get()
        {
            var rng = new Random();
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateTime.Now.AddDays(index),
                TemperatureC = Random.Shared.Next(-20, 55),
                Summary = Summaries[Random.Shared.Next(Summaries.Length)]
            })
            .ToArray();
        }
    }
}
            

Key attributes:

• [ApiController]: Enables API-specific behaviors like attribute routing and automatic model validation.
• [Route("[controller]")]: Defines the base route for this controller. In this case, it will be /weatherforecast.
• [HttpGet]: Specifies that the Get() method handles HTTP GET requests.
• ControllerBase: The base class for API controllers, providing access to common framework features.

Testing Your API

If you enabled OpenAPI support (Swagger), you can test your API directly from your browser:

1. Run your application.
2. Navigate to https://localhost:5001/swagger/index.html (or your application's specific Swagger URL).
3. You'll see an interactive documentation page where you can try out the endpoints. Click on the WeatherForecast endpoint, then "Try it out", and "Execute".

Alternatively, you can use tools like Postman or curl to send requests to your API endpoints.