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

Answer 2

You can consider using the model binding feature of the framework

According to documentation here: Customize model binding behavior with attributes

MVC contains several attributes that you can use to direct its default model binding behavior to a different source. For example, you can specify whether binding is required for a property, or if it should never happen at all by using the [BindRequired] or [BindNever] attributes.

So I suggest you add a BindRequiredAttribute to the model property.

public class QueryParameters {     [BindRequired]     public int A { get; set; }     public int B { get; set; } } 

From there the framework should be able to handle the binding and updating model state so that you can check the state of the model in the action

[Route("api/[controller]")] public class ValuesController : Controller {     // GET api/values     [HttpGet]     public IActionResult Get([FromQuery]QueryParameters parameters)     {             if (ModelState.IsValid)         {             return Ok(new [] { parameters.A.ToString(), parameters.B.ToString() });         }         return BadRequest();     }         } 

The other option would be to create a custom model binder that would fault the action if the required query string is not present.

Reference: Custom Model Binding