Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using EmployeeApp.Models;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace EmployeeApp
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

   
        public void ConfigureServices(IServiceCollection services)
        {
            services.Configure<Microsoft.AspNetCore.Mvc.CookieTempDataProviderOptions>(options => {
                options.Cookie.IsEssential = true;
            });
            services.AddMemoryCache();
            services.AddSession();
            services.AddControllersWithViews();
            services.AddDbContext<EmployeeDbContext>(options =>
             options.UseSqlServer(Configuration["Data:connectionString"]));

        }

        
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            // just in order to create database if not existing
            using (var serviceScope = app.ApplicationServices.GetService<IServiceScopeFactory>().CreateScope())
            {
                var context = serviceScope.ServiceProvider.GetRequiredService<EmployeeDbContext>();
                context.Database.EnsureCreated();
            }

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
            }
            app.UseStaticFiles();

            app.UseRouting();

            app.UseSession();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Home}/{action=Index}/{id?}");
            });
        }
    }
}