How to validate a required query string field using model validation in ASP.NET Core

Question

Given following API

public class PagedRequest
{
  [Required, Range(1, 100, ErrorMessage = "Limit must be from 1 to 100.")]
  public int Top { get; set; }

  [Required, Range(0, int.MaxValue, ErrorMessage = "Skip must be 0 or greater.")]
  public int Skip { get; set; }
}

[Route("test")]
[HttpGet]
public ActionResult<BarResponse> GetFoos([FromQuery] PagedRequest request)
{
  if (!ModelState.IsValid) return BadRequest(ModelState);

  // Return 200 OK with data here
}

Works as expected:

test?skip=0&top=10 -> returns 200
test?skip=0&top=0 -> returns BadRequest with error messages

Doesn't work as expected

test?top=0, returns 200 OK, expected required field validation error for Skip field.

Notes:

Using ASP.NET Core 3.0
This used to work with FromUri in ASP.NET Framework 4.x, then I'ld use a non-parameterless constructor, which is no longer allowed

Thanks @KirkLarkin. Using [BindRequired] makes it work without changing to nullable ints. If you want to add that as an answer I'll mark it as the accepted answer. — Bernard Vander Beken
– Bernard Vander Beken, Commented Nov 20, 2019 at 14:52
@KirkLarkin is correct. Here is a link to docs to support the provided suggestion learn.microsoft.com/en-us/aspnet/core/mvc/models/… — Nkosi
– Nkosi, Commented Nov 20, 2019 at 15:04

Kirk Larkin · Accepted Answer · 2019-11-20 15:34:51Z

5

You can replace the [Required] attribute with the [BindRequired] attribute, which:

Causes model binding to add a model state error if binding cannot occur for a model's property.

public class PagedRequest
{
    [BindRequired, Range(1, 100, ErrorMessage = "Limit must be from 1 to 100.")]
    public int Top { get; set; }

    [BindRequired, Range(0, int.MaxValue, ErrorMessage = "Skip must be 0 or greater.")]
    public int Skip { get; set; }
}

answered Nov 20, 2019 at 15:34

community wiki

Kirk Larkin

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Comments

Bernard Vander Beken · Accepted Answer · 2023-08-29 06:59:29Z

1

It's likely you're missing the ApiController attribute on your Controller class. This attribute applies a couple of default conventions which are common for web APIs, but uncommon for web pages. Although honestly I can't really figure out which convention it is that makes your sample work. It probably has something to do with the model binder.

See: https://learn.microsoft.com/en-us/aspnet/core/web-api/?view=aspnetcore-3.0#apicontroller-attribute

Additionally, with the ApiController attribute you no longer need to check to model state yourself. If the model state is invalid, ASP.NET Core MVC will automatically return a bad request response. So you can remove this part after applying the attribute:

if (!ModelState.IsValid) return BadRequest(ModelState);

edited Aug 29, 2023 at 6:59

Bernard Vander Beken

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answered Nov 21, 2019 at 9:53

Nick Muller

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