Building a Simple ASP.NET Core Web API

Step 1: Create a New ASP.NET Core Web API Project

Open your terminal or command prompt and use the .NET CLI to create a new Web API project:

dotnet new webapi -n MySimpleApi
cd MySimpleApi

This command creates a new project named MySimpleApi with a default project structure and a sample controller.

Step 2: Define Your Data Model

Let's create a simple model to represent the data we'll be working with. Create a new folder named Models in your project root and add a new C# file called TodoItem.cs.

namespace MySimpleApi.Models
{
    public class TodoItem
    {
        public long Id { get; set; }
        public string Name { get; set; }
        public bool IsComplete { get; set; }
    }
}

Step 3: Create a Web API Controller

ASP.NET Core uses controllers to handle incoming HTTP requests. Replace the contents of the generated Controllers/WeatherForecastController.cs file with the following code for a TodoItemsController. You can also create a new controller file in the Controllers folder.

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

namespace MySimpleApi.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class TodoItemsController : ControllerBase
    {
        private static List<TodoItem> _todoItems = new List<TodoItem>
        {
            new TodoItem { Id = 1, Name = "Learn ASP.NET Core", IsComplete = false },
            new TodoItem { Id = 2, Name = "Build a Web API", IsComplete = false },
            new TodoItem { Id = 3, Name = "Deploy the API", IsComplete = false }
        };

        // GET: api/TodoItems
        [HttpGet]
        public ActionResult<IEnumerable<TodoItem>> GetAllTodoItems()
        {
            return Ok(_todoItems);
        }

        // GET: api/TodoItems/5
        [HttpGet("{id}", Name = "GetTodoItem")]
        public ActionResult<TodoItem> GetTodoItem(long id)
        {
            var todoItem = _todoItems.FirstOrDefault(t => t.Id == id);
            if (todoItem == null)
            {
                return NotFound();
            }
            return Ok(todoItem);
        }

        // POST: api/TodoItems
        [HttpPost]
        public ActionResult<TodoItem> CreateTodoItem([FromBody] TodoItem todoItem)
        {
            todoItem.Id = _todoItems.Count + 1;
            _todoItems.Add(todoItem);
            return CreatedAtRoute("GetTodoItem", new { id = todoItem.Id }, todoItem);
        }

        // PUT: api/TodoItems/5
        [HttpPut("{id}")]
        public IActionResult UpdateTodoItem(long id, [FromBody] TodoItem updatedTodoItem)
        {
            var todoItem = _todoItems.FirstOrDefault(t => t.Id == id);
            if (todoItem == null)
            {
                return NotFound();
            }

            todoItem.Name = updatedTodoItem.Name;
            todoItem.IsComplete = updatedTodoItem.IsComplete;

            return NoContent();
        }

        // DELETE: api/TodoItems/5
        [HttpDelete("{id}")]
        public IActionResult DeleteTodoItem(long id)
        {
            var todoItem = _todoItems.FirstOrDefault(t => t.Id == id);
            if (todoItem == null)
            {
                return NotFound();
            }

            _todoItems.Remove(todoItem);
            return NoContent();
        }
    }
}

In this controller:

• [Route("api/[controller]")] sets the base route for this controller to /api/TodoItems.
• [ApiController] attribute enables API-specific behaviors.
• We use a static list to simulate a database for simplicity.
• HTTP methods like [HttpGet], [HttpPost], [HttpPut], and [HttpDelete] define the endpoints for different operations.

Step 4: Run Your API

Save your changes and run the application from your terminal:

dotnet run

The application will start, and you'll see output indicating the URLs where your API is listening. Typically, this will include a local URL like https://localhost:5001 or http://localhost:5000.

By default, ASP.NET Core Web API projects include Swagger/OpenAPI support. You can access the interactive API documentation by navigating to /swagger in your browser (e.g., https://localhost:5001/swagger). This provides a user-friendly interface to test your API endpoints directly.