InvalidOperationException: Unable to resolve service for type 'Microsoft.AspNetCore.Identity.RoleManage

Question

I am working netCore 2.1 and I have this problem:

An unhandled exception occurred while processing the request.

InvalidOperationException: Unable to resolve service for type 'Microsoft.AspNetCore.Identity.RoleManager`1[Microsoft.AspNetCore.Identity.IdentityRole]' while attempting to activate 'sistemaAC.Areas.Identity.Pages.Account.RegisterModel'.

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Text.Encodings.Web;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Identity.UI.Services;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.Extensions.Logging;

        public RegisterModel(
            UserManager<IdentityUser> userManager,
            SignInManager<IdentityUser> signInManager,
            ILogger<RegisterModel> logger,
            IEmailSender emailSender,
            RoleManager<IdentityRole> roleManager)
        {
            _userManager = userManager;
            _signInManager = signInManager;
            _logger = logger;
            _emailSender = emailSender;
            _roleManager = roleManager;
        }

        [BindProperty]
        public InputModel Input { get; set; }

        public string ReturnUrl { get; set; }

        public class InputModel
        {
            [Required]
            [EmailAddress]
            [Display(Name = "Email")]
            public string Email { get; set; }

            [Required]
            [StringLength(100, ErrorMessage = "The {0} must be at least {2} and at max {1} characters long.", MinimumLength = 6)]
            [DataType(DataType.Password)]
            [Display(Name = "Password")]
            public string Password { get; set; }    
            [DataType(DataType.Password)]
            [Display(Name = "Confirm password")]
            [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
            public string ConfirmPassword { get; set; }
        }

        public void OnGet(string returnUrl = null)
        {
            ReturnUrl = returnUrl;
        }

        public async Task<IActionResult> OnPostAsync(string returnUrl = null)
        {
            returnUrl = returnUrl ?? Url.Content("~/");
            if (ModelState.IsValid)
            {
                var user = new IdentityUser { UserName = Input.Email, Email = Input.Email };
                var result = await _userManager.CreateAsync(user, Input.Password);
                if (result.Succeeded)
                {
                    _logger.LogInformation("User created a new account with password.");

                    var code = await _userManager.GenerateEmailConfirmationTokenAsync(user);
                    var callbackUrl = Url.Page(
                        "/Account/ConfirmEmail",
                        pageHandler: null,
                        values: new { userId = user.Id, code = code },
                        protocol: Request.Scheme);

                    await _emailSender.SendEmailAsync(Input.Email, "Confirm your email",
                        $"Please confirm your account by <a href='{HtmlEncoder.Default.Encode(callbackUrl)}'>clicking here</a>.");


                    var xRol = await _roleManager.RoleExistsAsync("Administrador");
                    if(!xRol)
                    {
                        var role = new IdentityRole("Administrador");
                        var res = await _roleManager.CreateAsync(role);

                        if (res.Succeeded)
                        {
                            await _userManager.AddToRoleAsync(user, "Administrador");
                            await _signInManager.SignInAsync(user, isPersistent: false);

                        }
                    }
                    else
                    {
                        await _userManager.AddToRoleAsync(user, "Administrador");
                        await _signInManager.SignInAsync(user, isPersistent: false);
                    }

                    xRol = await _roleManager.RoleExistsAsync("Usuario");
                    if (!xRol)
                    {
                        var role = new IdentityRole();
                        role.Name = "Usuario";
                        await _roleManager.CreateAsync(role);
                    }

                    xRol = await _roleManager.RoleExistsAsync("Asistente");
                    if (!xRol)
                    {
                        var role = new IdentityRole();
                        role.Name = "Asistente";
                        await _roleManager.CreateAsync(role);

                    }
                    return LocalRedirect(returnUrl);


                }
                foreach (var error in result.Errors)
                {
                    ModelState.AddModelError(string.Empty, error.Description);
                }
            }   
            // If we got this far, something failed, redisplay form
            return Page();
        }
    }
}

Answer 1

I was facing the same issue. I found the answer on this thread: Unable to resolve service for type 'Microsoft.AspNetCore.Identity.RoleManager`

Based upon the code above, I assumed you scaffolded in the Identity services. The generated code creates a /Areas/Identity/IdentityHostingStartup.cs class. You need to change the line of code

services.AddDefaultIdentity<IdentityUser>

to

services.AddIdentity<IdentityUser,IdentityRole>

Per request, here is my full AddIdentity code

services.AddIdentity<IdentityUser,IdentityRole>(options =>
{
    //option settings...
})
.AddEntityFrameworkStores<IdentityDbContext>()
.AddDefaultUI()
.AddDefaultTokenProviders();