Build a simple RESTful API in .NET 5 (ASP.Net Core)

A simple tutorial on how to create a quick RESTful API in .NET 5

Prerequisites

• IDE of choice (I recommend Visual Studio or Jetbrains Rider)
• .NET 5 SDK (https://dotnet.microsoft.com/download/visual-studio-sdks)

This guide is for those who are quite new to ASP.NET Core development and have some knowledge about RESTful APIs and C# Development. The main goal of this guide is to quickly explain how to create a REST API and return some data.

Getting Started

Create a new project and choose the ASP.NET Core Web API

Create A New ASP.NET Core Web API

This creates a simple project that includes 1 default API Controller (WeatherForecastController.cs)

How your solution should look after creating a new project.

Creating our Classes and Methods

For the next step, we’ll remove the existing WeatherForecast controller and object and create a new domain object/class (User)

1. Create a User Class.

User.cs

public class User
{
    public Guid Guid { get; set; }

    public string Email { get; set; }

    public string Password { get; set; }

    public string Name { get; set; }

    public User()
    {
        
    }
}

2. Create a UsersController class inside the Controllers folder and define the following methods (no worries I’ll explain how everything works):

UsersController.cs

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

namespace SimpleAPI.Controllers
{
    [Controller]
    [Route("api/[controller]")]
    public class UsersController : Controller
    {
        private readonly List<User> _users = new List<User>();

        public UsersController()
        {
            _users.Add(new User()
            {
                Email = "john@example.com",
                Name = "John Doe",
                Password = "password123",
                Guid = Guid.NewGuid()
            });
            
            _users.Add(new User()
            {
                Email = "jane@example.com",
                Name = "Jane Doe",
                Password = "password123",
                Guid = Guid.Parse("587671b5-3c0a-46e9-9015-624220c614ca")
            });
        }

        [HttpGet]
        public ActionResult<List<User>> Index()
        {
            return _users; //returns all users.
        }

        [HttpGet("{guid}")]
        public ActionResult<User> GetByGuid(Guid guid)
        {
            return Ok(_users.FirstOrDefault(u => u.Guid == guid));
        }

        [HttpPost]
        public ActionResult<User> Insert([FromBody] User user)
        {
            _users.Add(user);
            return user;
        }
     
    }
}
Explanation:
[Controller]
[Route("api/[controller]")]
public class UsersController : Controller

The above code tells ASP.NET Core that this is a controller and lists on the /api/[controllername] endpoint. (In this case: /api/users)

The endpoints themselves are added by using the [HttpGet]/[HttpPost]/[HttpPut]/[HttpDelete] annotations.

[HttpGet]
public ActionResult<List<User>> Index()
{
    return _users; //returns all users.
}

Returns all users, ASP.NET Core will automatically change your C# object to JSON.

[HttpGet("{guid}")]
public ActionResult<User> GetByGuid(Guid guid)
{
    return Ok(_users.FirstOrDefault(u => u.Guid == guid));
}

Returns a specified user by its Guid. The [HttpGet(“{guid}] annotation tells the endpoint which parameter it needs.

[HttpPost]
public ActionResult<User> Insert([FromBody] User user)
{
    _users.Add(user);
    return user;
}

Accepts a user and adds it to the in-memory user list.

That’s all there is to it.

3. Start the application (It should open a browser window if not goto: https://localhost:5001/swagger/index.html)

Don’t see a swagger page?

In Startup.cs make sure your ConfigureServices method has

services.AddSwaggerGen(c => { c.SwaggerDoc("v1", new OpenApiInfo {Title = "SimpleAPI", Version = "v1"}); });

And Configure has

if (env.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
    app.UseSwagger();
    app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "SimpleAPI v1"));
}

Fetching data from the API using Swagger

In .NET 5 the standard Web API will automatically add a swagger documentation page. This allows you to easily test/use your Rest API while developing it.

Click on Try it out and Execute. It should return all users in the JSON format.

[
  {
    "guid": "fa4b96fc-f4aa-44fc-a5ed-b3f7dbf80bf1",
    "email": "john@example.com",
    "password": "password123",
    "name": "John Doe"
  },
  {
    "guid": "587671b5-3c0a-46e9-9015-624220c614ca",
    "email": "jane@example.com",
    "password": "password123",
    "name": "Jane Doe"
  }
]

This basically creates a GET call to https://localhost:5001/api/users If you go there yourself you’ll also get a JSON response with all existing users.

Feel free to try the other Swagger actions/methods.

Want to read more about this topic? Check out my full tutorial on creating a CRUD RESTFul API in .NET 5 using MongoDB

Thanks for reading, hope you’ve learned something.