c# - Required query string parameter in ASP.NET Core

Question

Using ASP.NET Core 1.1 with VS2015 (sdk 1.0.0-preview2-003131), I have the following controller:

public class QueryParameters
{
    public int A { get; set; }
    public int B { get; set; }
}

[Route("api/[controller]")]
public class ValuesController : Controller
{
    // GET api/values
    [HttpGet]
    public IEnumerable<string> Get([FromQuery]QueryParameters parameters)
    {
        return new [] { parameters.A.ToString(), parameters.B.ToString() };
    }        
}

As you can see, I have two query parameters. What I would like is to have one of them (ex: A) to be required. That is, I would like to use an attribute (if possible) to say that this attribute is required. Then, I would like like ASP.NET to do this validation before even calling my controller.

I would have liked to use the Newtonsoft RequiredAttribute to use the same attributes as I already use to validate the required properties in the PUT/POST content, but since the url is not a JSON string, it is obviously not used.

Any suggestion to have ASP.NET Core automatically check for required query parameters?

Note that I know that I can code the check myself using nullable query parameters but that beats the purpose of letting ASP.NET do the validation before calling my controller, thus keeping my controller tidy.

Answer 1

In ASP.NET Core 2.1 and above you can use top level parameters validation. You can put attributes on parameters

    [HttpGet]
    public IActionResult GetDices([BindRequired, Range(1, 6)]int number)
    {
        if (!ModelState.IsValid)
        {
            return BadRequest("Invalid number");
        }

            return Ok(_diceRepo.GetDices(number));
    }

More about this https://programmingcsharp.com/asp-net-parameter-validation/#Top-level_node_validation