MVC controller should return 400 when validation query string parameters

Question

Say you have a simple method in a MVC controller...

[Route("{id}", Name = "GetById")]
[HttpGet]
[ProducesResponseType(typeof(SomeType), (int)HttpStatusCode.OK)]
[ProducesResponseType(typeof(string), (int)HttpStatusCode.Unauthorized)]
[ProducesResponseType(typeof(string), (int)HttpStatusCode.Forbidden)]
[ProducesResponseType(typeof(string), (int)HttpStatusCode.BadRequest)]
[ProducesResponseType(typeof(string), (int)HttpStatusCode.ServiceUnavailable)]
public async Task<IActionResult> Get(string id, bool? includeNonActive = false)
{
    // some stuff
}

Is there any way to get MVC to automagically return a HTTP 400 if invalid value (non-boolean) are passed to the includeNonActive query string parameter?

HTTP GET http://my-server/api/12321312?includeNonActive=thisIsNotABooleanValue

Sure, I can accept a string type for 'includeNonActive', use Boolean.TryParse() and return BadRequest("wtf"), but that looks ugly in Swagger.

Answer 1

Is there any way to get MVC to automagically return a HTTP 400 if invalid value (non-boolean) are passed to the 'includeNonActive' query string parameter?

Sure, you could build an action filter for this.

[AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
public class EnsureBooleanQueryParameterAttribute : ActionFilterAttribute
{
    public EnsureBooleanQueryParameterAttribute(string parameterName)
    {
        if (string.IsNullOrEmpty(parameterName))
            throw new ArgumentException($"'{nameof(parameterName)}' is required.");
        this.ParameterName = parameterName;
    }

    public string ParameterName { get; set; }

    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        var attribute = (EnsureBooleanQueryParameterAttribute)filterContext.ActionDescriptor
            .GetCustomAttributes(typeof(EnsureBooleanQueryParameterAttribute), true)
            .FirstOrDefault();

        // The attribute exists on the current action method
        if (attribute != null)
        {
            string param = filterContext.HttpContext.Request.QueryString[attribute.ParameterName];
            bool result;
            // If the query string value is present and not boolean
            if (!string.IsNullOrEmpty(param) && !bool.TryParse(param, out result))
            {
                filterContext.Result = new HttpStatusCodeResult(400, 
                    "Invalid boolean query string value for '{attribute.ParameterName}'.");
            }
        }
    }
}

And then use the filter like:

[Route("{id}", Name = "GetById")]
[HttpGet]
[ProducesResponseType(typeof(SomeType), (int)HttpStatusCode.OK)]
[ProducesResponseType(typeof(string), (int)HttpStatusCode.Unauthorized)]
[ProducesResponseType(typeof(string), (int)HttpStatusCode.Forbidden)]
[ProducesResponseType(typeof(string), (int)HttpStatusCode.BadRequest)]
[ProducesResponseType(typeof(string), (int)HttpStatusCode.ServiceUnavailable)]
[EnsureBooleanQueryParameter("includeNonActive")]
public async Task<IActionResult> Get(string id, bool? includeNonActive = false)
{
    // some stuff
}

You could use this as a starting point and add an Enum parameter that you can use to specify the data type and a bool parameter to indicate whether or not the value is required to exist in the URL.