Unable to resolve service for type 'Microsoft.AspNetCore.Identity.RoleManager

Question

I hope that you are all doing well! I am getting the following error:

InvalidOperationException: Unable to resolve service for type 'Microsoft.AspNetCore.Identity.RoleManager`1[Microsoft.AspNetCore.Identity.IdentityUser]' while attempting to activate 'july_15_auth.Controllers.AccountController' 

I have spent weeks trying to solve the error, reading the forums here, and other websites. The comments online have suggested to modify my Startup.cs file, but I have tried many different ways, yet I still cannot figure out why this is not work. Any suggestions would be greatly appreciated.

This is my AccountController file

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using july_15_auth.Models;
using july_15_auth.ViewModels;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Mvc;

namespace july_15_auth.Controllers
{
    public class AccountController : Controller
    {
            private readonly UserManager<IdentityUser> userManager;
            private readonly SignInManager<IdentityUser> signInManager;
        private readonly RoleManager<IdentityUser> roleManager;

    public AccountController(UserManager<IdentityUser> userManager,
            SignInManager<IdentityUser> signInManager, RoleManager<IdentityUser> roleManager)
        {
            this.userManager = userManager;
            this.signInManager = signInManager;
        this.roleManager = roleManager;
    }
        [AcceptVerbs("Get", "Post")]
        public async Task<IActionResult> IsEmailInUse(string email)
        {
            var user = await userManager.FindByEmailAsync(email);
            if(user == null) { return Json(true); }
            else { return Json($"Email {email} is already in use"); }
        }



            [HttpGet]
            public IActionResult Register()
            {
                return View();
            }

            [HttpPost]
            public async Task<IActionResult> Register(RegisterViewModel model)
            {
                if (ModelState.IsValid)
                {
                    // Copy data from RegisterViewModel to IdentityUser
                    var user = new IdentityUser
                    {
                        UserName = model.Email,
                        Email = model.Email
                    };

                    // Store user data in AspNetUsers database table
                    var result = await userManager.CreateAsync(user, model.Password);

                    // If user is successfully created, sign-in the user using
                    // SignInManager and redirect to index action of HomeController
                    if (result.Succeeded)
                    {
                        await signInManager.SignInAsync(user, isPersistent: false);
                        return RedirectToAction("index", "home");
                    }

                    // If there are any errors, add them to the ModelState object
                    // which will be displayed by the validation summary tag helper
                    foreach (var error in result.Errors)
                    {
                        ModelState.AddModelError(string.Empty, error.Description);
                    }
                }

                return View(model);
            }

            [HttpPost]
            
            public async Task<IActionResult> Logout()
            {
            await signInManager.SignOutAsync();
            return RedirectToAction("index", "home");
            }

        [HttpGet]
        public IActionResult Login()
        {
            return View();
        }

        // Redirect Vulnerability Fix

        [HttpPost]
        public async Task<IActionResult> Login(LoginViewModel model, string returnUrl)
        {
            if (ModelState.IsValid)
            {
                var result = await signInManager.PasswordSignInAsync(
                    model.Email, model.Password, model.RememberMe, false);

                if (result.Succeeded)
                {
                    if(!string.IsNullOrEmpty(returnUrl))
                    {
                        return LocalRedirect(returnUrl);
                    }

                    return RedirectToAction("index", "home");
                }

                ModelState.AddModelError(string.Empty, "Invalid Login Attempt");
            }

            return View(model);
        }


    }
    }

This Is My Startup.cs file

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using july_15_auth.Models;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace july_15_auth
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
            services.AddDbContext<AppDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DevConnection")));
            services.AddTransient<IEmployeeRepository, MockEmployeeRepository>();
            services.AddIdentity<IdentityUser, IdentityRole>()
                .AddEntityFrameworkStores<AppDbContext>();
            services.Configure<IdentityOptions>(options =>
            {
                options.Password.RequiredLength = 7;
                options.Password.RequiredUniqueChars = 2;
                options.Password.RequireNonAlphanumeric = false; 
            });
           
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
            }
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthentication();
            app.UseAuthorization();

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

Answer 1

InvalidOperationException: Unable to resolve service for type 'Microsoft.AspNetCore.Identity.RoleManager`1[Microsoft.AspNetCore.Identity.IdentityUser]' while attempting to activate 'july_15_auth.Controllers.AccountController'

To fix above exception, please try to replace RoleManager<IdentityUser> with RoleManager<IdentityRole> while you inject an instance of RoleManager in your controller.

private readonly UserManager<IdentityUser> userManager;
private readonly SignInManager<IdentityUser> signInManager;
private readonly RoleManager<IdentityRole> roleManager;

public AccountController(UserManager<IdentityUser> userManager,
        SignInManager<IdentityUser> signInManager, RoleManager<IdentityRole> roleManager)
{
    this.userManager = userManager;
    this.signInManager = signInManager;
    this.roleManager = roleManager;
}

For more information about RoleManager<TRole>, please check: https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.identity.rolemanager-1?view=aspnetcore-3.1