Error Logging

using System;
using System.Web;
using System.Web.Mvc;

namespace Example.SDK.Filters
{
    [AttributeUsage(AttributeTargets.Class, Inherited = false, AllowMultiple = false)]
    public sealed class CustomErrorHandlerFilter : HandleErrorAttribute
    {
        public override void OnException(ExceptionContext filterContext)
        {
            // RouteDate is useful for retrieving info like controller, action or other route values
            string controllerName = filterContext.RouteData.Values["controller"].ToString();
            string actionName = filterContext.RouteData.Values["action"].ToString();

            string exception = filterContext.Exception.ToString(); // Full exception stack
            string message = filterContext.Exception.Message; // Message given by the exception

            // Log the exception within database
            LogExtensions.Insert(exception.ToString(), message, controllerName + "." + actionName);

            base.OnException(filterContext);
        }
    }
}

filters.Add(new CustomErrorHandlerFilter());

public ActionResult Details( string product)
{
   ....
    if (productNotFound) {
        // https://www.eidias.com/blog/2014/7/2/mvc-custom-error-pages
        Response.Clear();
        Response.TrySkipIisCustomErrors = true;
        Response.Write(product + " product not exists");
        Response.StatusCode = (int)HttpStatusCode.NotFound;
        Response.End();
        return null;
    }

public class ErrorLogger : HandleErrorAttribute
{
    public override void OnException(ExceptionContext filterContext)
    {

        string strLogText = "";
        Exception ex = filterContext.Exception;
        filterContext.ExceptionHandled = true;
        var objClass = filterContext;
        strLogText += "Message ---\n{0}" + ex.Message;

        if (ex.Source == ".Net SqlClient Data Provider")
        {
            strLogText += Environment.NewLine + "SqlClient Error ---\n{0}" + "Check Sql Error";
        }
        else if (ex.Source == "System.Web.Mvc")
        {
            strLogText += Environment.NewLine + ".Net Error ---\n{0}" + "Check MVC Code For Error";
        }
        else if (filterContext.HttpContext.Request.IsAjaxRequest() == true)
        {
            strLogText += Environment.NewLine + ".Net Error ---\n{0}" + "Check MVC Ajax Code For Error";
        }
        strLogText += Environment.NewLine + "Source ---\n{0}" + ex.Source;
        strLogText += Environment.NewLine + "StackTrace ---\n{0}" + ex.StackTrace;
        strLogText += Environment.NewLine + "TargetSite ---\n{0}" + ex.TargetSite;
        if (ex.InnerException != null)
        {
            strLogText += Environment.NewLine + "Inner Exception is {0}" + ex.InnerException;//error prone
        }
        if (ex.HelpLink != null)
        {
            strLogText += Environment.NewLine + "HelpLink ---\n{0}" + ex.HelpLink;//error prone
        }

        StreamWriter log;

        string timestamp = DateTime.Now.ToString("d-MMMM-yyyy", new CultureInfo("en-GB"));

        string error_folder = ConfigurationManager.AppSettings["ErrorLogPath"].ToString();

        if (!System.IO.Directory.Exists(error_folder))
        {
            System.IO.Directory.CreateDirectory(error_folder);
        }

        if (!File.Exists(String.Format(@"{0}\Log_{1}.txt", error_folder, timestamp)))
        {
            log = new StreamWriter(String.Format(@"{0}\Log_{1}.txt", error_folder, timestamp));
        }
        else
        {
            log = File.AppendText(String.Format(@"{0}\Log_{1}.txt", error_folder, timestamp));
        }

        var controllerName = (string)filterContext.RouteData.Values["controller"];
        var actionName = (string)filterContext.RouteData.Values["action"];

        // Write to the file:
        log.WriteLine(Environment.NewLine + DateTime.Now);
        log.WriteLine("------------------------------------------------------------------------------------------------");
        log.WriteLine("Controller Name :- " + controllerName);
        log.WriteLine("Action Method Name :- " + actionName);
        log.WriteLine("------------------------------------------------------------------------------------------------");
        log.WriteLine(objClass);
        log.WriteLine(strLogText);
        log.WriteLine();

        // Close the stream:
        log.Close();
        filterContext.HttpContext.Session.Abandon();
        filterContext.Result = new RedirectToRouteResult
         (new RouteValueDictionary 
         {
                 {"controller", "Errorview"}, {"action", "Error"}
         });

    }

}

<add key="ErrorLogPath" value="C:\ErrorLog\DemoMVC\" />

public class FilterConfig
{
    public static void RegisterGlobalFilters(GlobalFilterCollection filters)
    {
        filters.Add(new ErrorLogger());
    }
}