Validation Attribute ASP.NET Core

Question

I am migrating my MVC .NET Framework 4.7.2 App to a .NET Core 2.1 App.

My ViewModel is as below:

public class MyViewModel, IValidatableObject
{
    [Required(ErrorMessage = "Please enter a name")]
    public string Name { get; set; }

    //Other props removed for brevity
}

I have an ajax call to save the data on screen which hits an API with a JsonValidationFilter attribute like below:

    [HttpPost]
    [JsonValidationFilter]
    [Route("api/MyController/Id}/Save")]
    public async Task<IActionResult> SaveAsync(int Id, MyViewModel model)
    {
        //code removed for brevity
        _myService.Save();

        return Ok();
    }

So the code in my ValidationFilter for the .NET Framework version of the application is as below:

public class JsonValidationFilterAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(HttpActionContext actionContext)
    {
        if (actionContext.ModelState.IsValid) return;
        var errorMessages = actionContext.ModelState.Values
            .SelectMany(modelState => modelState.Errors.Select(x => x.ErrorMessage));
        actionContext.Response = actionContext.Request.CreateErrorResponse(HttpStatusCode.BadRequest, Json.Encode(errorMessages));
    }
}

And if I try to save the screen with a name I get into the error function of my Ajax call and the Validation Alert appears and the validation error is contained in the xhr.responseText so it displays as expected.

                error: function (xhr) {

                    $(saveAlertTarget).html('<span class="glyphicon glyphicon-warning-sign"></span>There was a problem with the last save attempt');
                    if (xhr.status == '400') {
                        displayErrorMessage("Please fix validation errors before saving", xhr.responseText);
                    }
                }

I have attempted to rewrite the validation filter in .NET Core as below - and I do get into the error part of my Ajax call with a 400 request so the Validation alert displays but it never builds up the message fully because xhr.responseText is always blank - have I missed something setting this up?

My .NET Core JsonValidationFilter

public class JsonValidationFilterAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext actionContext)
    {
        if (actionContext.ModelState.IsValid) return;
        IEnumerable<string> errorMessages = actionContext.ModelState.Values.SelectMany(modelState => modelState.Errors.Select(x => x.ErrorMessage));
        actionContext.Result = new BadRequestObjectResult(errorMessages);
    }
}

Can you check in your browser whether the response actually contains a body? — poke
– poke, Commented Jan 8, 2019 at 16:05
@poke - just looking a Dev Tools on Chrome and in Network Tab I do see a response ["Please enter a name"] - but that isnt getting picked up in the error function of my Ajax call — Ctrl_Alt_Defeat
– Ctrl_Alt_Defeat, Commented Jan 8, 2019 at 16:16
Very strange - now it appears that xhr.responseText is getting the data but it isnt getting displayed in alert - will need to look into the displayErrorMessage function — Ctrl_Alt_Defeat
– Ctrl_Alt_Defeat, Commented Jan 8, 2019 at 16:22

Ctrl_Alt_Defeat · Accepted Answer · 2019-01-08 16:50:11Z

1

This was an issue with my displayErrorMessage java script function - the C# .NET Core Json Validation Filter was working as expected

answered Jan 8, 2019 at 16:50

Ctrl_Alt_Defeat

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