WEB API validation class using attributes

I could swear that some time ago I was able to debug it and go to Validation class, but now it seems that is only regarding some client validation and it does not validate in backend middleware.

Be sure that your razor view does not add jquery.validate.min.js and jquery.validate.unobtrusive.min.js.

For using asp.net core default template,you could just avoid using the following code in your razor view:

@*@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}*@

Then add the following code to your backend:

if (!ModelState.IsValid)  
{
    return View(model);
}

Update:

If you want to validate before controller,I suggest that you could custom ActionFilter.Here is a working demo with asp.net core 3.1 web api:

Model:

public class Test
{
    [Range(1,4)]
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
}

Custom ActionFilter:

public class ValidationFilter : IActionFilter
{
    public void OnActionExecuted(ActionExecutedContext context)
    {
    }

    public void OnActionExecuting(ActionExecutingContext context)
    {
        if (!context.ModelState.IsValid)
        {
            context.Result = new JsonResult(context.ModelState.Select(m=>m.Value).ToList())
            {
                StatusCode = 400
            };
        }
    }
}

Controller:

[Route("api/[controller]")]
public class ValuesController : ControllerBase
{
    // POST api/<controller>
    [HttpPost]
    public void Post(Test test)
    {

    }
}

Register in Startup.cs:

services.AddControllers(config =>
{
    config.Filters.Add(new ValidationFilter());
});

Result: