Using ActionFilterAttribute to validate all form input

Combining ActionFilterAttribute with ModelState

I'm going to start with a file called ValidationActionFilterAttribute because it is a verbose name that defines exactly what it is doing. Here is a shell of the class that extends the action filter:

using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http.Filters;
namespace Filters
{
    public class ValidationActionFilterAttribute : ActionFilterAttribute, IActionFilter
    {
        public override void OnActionExecuting(System.Web.Http.Controllers.HttpActionContext actionContext)
        {
        }
    }
}

The core of the code will go inside the overridden OnActionExecuting function. Now I'm going to fill in the key if statement that will check if the ModelState is valid:

if (!actionContext.ModelState.IsValid)
{
	// TODO: Provide friendly error message
}

If the form is not valid, it will fall inside our if statement. The final piece of this is to provide a useful error message. Inside the actionContext.ModelState I can access the error messages with that variable. The final piece of the puzzle is to define the result with a 400 Bad Request response with the friendly error message:

actionContext.Response = actionContext.Request.CreateResponse(HttpStatusCode.BadRequest, actionContext.ModelState);

Here is the final results of the snippets:

using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http.Filters;
namespace Common.Filters
{
    public class ValidationActionFilterAttribute : ActionFilterAttribute, IActionFilter
    {
        public override void OnActionExecuting(System.Web.Http.Controllers.HttpActionContext actionContext)
        {
            if (!actionContext.ModelState.IsValid)
            {
				actionContext.Response = actionContext.Request.CreateResponse(HttpStatusCode.BadRequest, actionContext.ModelState);
            }
        }
    }
}

Published on Feb 1, 2020

Tags: Entity Framework Tutorials For Beginners and Professionals | modelstate