Web APIs

Introduction

ASP.NET Core is a cross-platform, high-performance framework for building modern, cloud-enabled, Internet-connected applications. With ASP.NET Core, you can build web apps, mobile backends, and APIs. This tutorial will guide you through creating a web API with ASP.NET Core from scratch.

Setting Up the Development Environment

Before you start, ensure you have the following installed:

• Visual Studio 2019 or later
• .NET Core SDK

https://dotnet.microsoft.com/download/dotnet-core

Creating a New ASP.NET Core Web API Project

Open Visual Studio and create a new project:

• Select "Create a new project".
• Choose "ASP.NET Core Web Application" and click "Next".
• Name your project and select the location to save it. Click "Create".
• In the "Create a new ASP.NET Core Web Application" dialog, select "API" and click "Create".

Understanding the Project Structure

The project template creates a simple project structure:

• Controllers - Contains the API controllers.
• Models - Contains the data models.
• Program.cs - Contains the entry point of the application.
• Startup.cs - Configures services and the app's request pipeline.

Creating a Model

In this tutorial, we will create a simple model for a "Product". Add a new class named Product.cs in the Models folder:

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
}

Creating a Controller

Create a new controller named ProductsController.cs in the Controllers folder:

using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;
using System.Linq;

namespace WebAPITutorial.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class ProductsController : ControllerBase
    {
        private static readonly List Products = new List
        {
            new Product { Id = 1, Name = "Product1", Price = 10.0M },
            new Product { Id = 2, Name = "Product2", Price = 20.0M }
        };

        [HttpGet]
        public ActionResult> GetProducts()
        {
            return Products;
        }

        [HttpGet("{id}")]
        public ActionResult GetProduct(int id)
        {
            var product = Products.FirstOrDefault(p => p.Id == id);
            if (product == null)
            {
                return NotFound();
            }
            return product;
        }

        [HttpPost]
        public ActionResult CreateProduct(Product product)
        {
            product.Id = Products.Count + 1;
            Products.Add(product);
            return CreatedAtAction(nameof(GetProduct), new { id = product.Id }, product);
        }
    }
}

Configuring the Application

Ensure that the Startup.cs file is correctly configured to use controllers:

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers();
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }

    app.UseHttpsRedirection();
    app.UseRouting();
    app.UseAuthorization();
    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
    });
}

Testing the API

Run the application by pressing F5 or clicking the "Run" button in Visual Studio. Use a tool like Postman to test your API endpoints:

• GET https://localhost:5001/api/products - Retrieve all products.
• GET https://localhost:5001/api/products/1 - Retrieve a product by ID.
• POST https://localhost:5001/api/products - Create a new product.

Conclusion

Congratulations! You have created a simple Web API with ASP.NET Core. This tutorial covered the basics of setting up a new project, creating models and controllers, configuring the application, and testing the API. From here, you can extend the API with more features and deploy it to a cloud service.