Why should you care?

Controllers are the front door of your API. Keep them thin: validate input, call a service, return a DTO. Fat controllers with SQL inside are hard to test and maintain.

See it live — copy this example

Create a Web API (dotnet new webapi), paste the example, run dotnet run, test in Swagger.

[ApiController]
[Route("api/[controller]")]
public class ProductsController : ControllerBase
{
    [HttpGet("{id:int}")]
    public ActionResult<ProductDto> Get(int id)
        => Ok(new ProductDto(id, "Demo Product", 99m));
}

Run Example »

Edit the code and click Run — like W3Schools Try it Yourself.

What happened?

• [ApiController] enables automatic model validation and binding rules.
• [Route("api/[controller]")] makes the URL /api/products for ProductsController.
• Inject services via constructor — ASP.NET creates them using DI.

Try it yourself

1. Add Controllers/ProductsController.cs to ShopNest.API.
2. Add [ApiController] and [Route("api/[controller]")].
3. Add one GET action returning a hard-coded ProductDto.
4. Change a route URL or DTO property and save — test again in Swagger or curl.
5. Return the wrong status code on purpose (404 instead of 200) and see what the client shows.

Remember

ControllerBase + [ApiController] for JSON APIs. One controller per resource group (Products, Orders). Inject services; do not new() up DbContext in actions.