What is a RESTful API and how do you implement one in .NET Core?

A RESTful API (Representational State Transfer Application Programming Interface) is a way of providing a standardized interface for interacting with web resources using the HTTP protocol. The basic idea is to use HTTP verbs (such as GET, POST, PUT, and DELETE) to perform CRUD (Create, Read, Update, Delete) operations on resources represented by URLs.

In .NET Core, you can implement a RESTful API using the ASP.NET Core framework. Here are the basic steps:

1. Create a new ASP.NET Core web application project.
2. Add a new controller class to the project.
3. In the controller class, add action methods for each of the CRUD operations you want to support.
4. Use HTTP verbs to map the action methods to URLs.
5. Use model binding to extract data from the request.
6. Use the IActionResult return type to send responses to the client.

For example, here is a simple controller that implements a RESTful API for managing a list of tasks:

[ApiController]
[Route("api/[controller]")]
public class TasksController : ControllerBase
{
    private readonly List<Task> _tasks;

    public TasksController()
    {
        _tasks = new List<Task>();
    }

    [HttpGet]
    public IActionResult Get()
    {
        return Ok(_tasks);
    }

    [HttpPost]
    public IActionResult Create(Task task)
    {
        _tasks.Add(task);
        return Ok();
    }

    [HttpPut("{id}")]
    public IActionResult Update(int id, Task task)
    {
        var existingTask = _tasks.FirstOrDefault(t => t.Id == id);
        if (existingTask == null)
        {
            return NotFound();
        }

        existingTask.Title = task.Title;
        existingTask.Description = task.Description;
        existingTask.DueDate = task.DueDate;

        return Ok();
    }

    [HttpDelete("{id}")]
    public IActionResult Delete(int id)
    {
        var existingTask = _tasks.FirstOrDefault(t => t.Id == id);
        if (existingTask == null)
        {
            return NotFound();
        }

        _tasks.Remove(existingTask);

        return Ok();
    }
}

In this example, the [ApiController] attribute specifies that this is a controller for an API, and the [Route("api/[controller]")] attribute specifies that the URL for this controller will start with "/api/tasks". The Get(), Create(), Update(), and Delete() methods correspond to the HTTP verbs GET, POST, PUT, and DELETE, respectively. The HttpPost and HttpPut methods use model binding to extract data from the request, and the IActionResult return type is used to send responses to the client.