.NET Core 2.1 Override Automatic Model Validation

Question

In the latest .NET Core 2.1, an automatic validation for the model state validation is introduced (https://blogs.msdn.microsoft.com/webdev/2018/02/02/asp-net-core-2-1-roadmap/#mvc).

Previously I could override the validation error response by the following code below:

public class ApiValidateModelAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext context)
    {
        if (!context.ModelState.IsValid)
        {
            context.Result = new BadRequestObjectResult(new context.ModelState);
        }

    base.OnActionExecuting(context);
}

But now it no longer works. The validation errors is responded without entering the override method.

Anyone has any clue? Thanks.

Ohm

It looks like you only need to remove the ApiController attribute. That would 'revert' the logic to the 'old' style. – Macomber

@Macomber you are absolutely right. Silly of me for not thinking of that. Thanks! – Ohm

Answer 1

If you'd like to keep using the ApiController attribute (which has other functions like disabling conventional routing and allowing model binding without adding [FromBody] parameter attributes), you might be able to do it via this in your Startup.cs file:

services.Configure<ApiBehaviorOptions>(opt =>
{
    opt.SuppressModelStateInvalidFilter = true;
});

That will make it so that if the ModelState is invalid it won't automatically return a 400 error.

Alizaalizarin

You save my life, I have been looking this code for a long time – Flagging

I also needed options.Filters.Add(typeof(ValidateModelAttribute)); in mvc options for this to work, see Daniel's answer. – Rhyner

Answer 2

I was recently asked by a friend about this and my approach was to replace the default ModalStateInvalidFilter by a custom one.

In my test I've implemented the suggestion from here and then:

services.AddMvc(options =>
{
    options.Filters.Add(typeof(ValidateModelAttribute));
});


services.Configure<ApiBehaviorOptions>(options => { options.SuppressModelStateInvalidFilter = true; });

Tekla

thanks for sharing this as well as the blog post :) – Vassily