如何从 register.cshtml 和 register.cshtml.cs 中的 AspNetRoles 表中构建下拉列表？

Question

I tried to build a drop-down list from the AspNetRoles table in register.cshtml and register.cshtml.cs but didn't get data from AspNetRoles in the register page.

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RoleController:

using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Mvc;

namespace login_and_registration.Controllers
{
    public class RoleController : Controller
    {
        //public IActionResult Index()
        //{
        //    return View();
        //}


        RoleManager<IdentityRole> roleManager;
        public RoleController(RoleManager<IdentityRole> roleManager)
        {
            this.roleManager = roleManager;
        }
        public IActionResult Index()
        {
            var roles = roleManager.Roles.ToList();
            return View(roles);
        }



        public IActionResult Create()
        {

            return View(new IdentityRole());
        }
        [HttpPost]
        public async Task<IActionResult> Create(IdentityRole role)
        {
            await roleManager.CreateAsync(role);
            return RedirectToAction("Index");
        }
    }
}

DbContext:

using login_and_registration.Areas.Identity.Data;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore;

namespace login_and_registration.Areas.Identity.Data;

public class lAppregistrationContext : IdentityDbContext<loginregistrationUser>
{
    public lAppregistrationContext(DbContextOptions<lAppregistrationContext> options)
        : base(options)
    {
    }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
        // Customize the ASP.NET Identity model and override the defaults if needed.
        // For example, you can rename the ASP.NET Identity table names and more.
        // Add your customizations after calling base.OnModelCreating(builder);
    }


}
      

Register.cshtml:

@page
@model RegisterModel
@using login_and_registration.Controllers
@{
    ViewData["Title"] = "Register";
    
           
}


<h1>@ViewData["Title"]</h1>
<div class="row">
    <div class="col-md-4">
        <form asp-route-returnUrl="@Model.ReturnUrl" method="post">
            <h4>Create a new account.</h4>
            <hr />
            <div asp-validation-summary="All" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Input.FirstName"></label>
                <input asp-for="Input.FirstName" class="form-control" />
                <span asp-validation-for="Input.FirstName" class="text-danger"></span>
            </div>
             <div class="form-group">
                <label asp-for="Input.LastName"></label>
                <input asp-for="Input.LastName" class="form-control" />
                <span asp-validation-for="Input.LastName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Input.Email"></label>
                <input asp-for="Input.Email" class="form-control" />
                <span asp-validation-for="Input.Email" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Input.Password"></label>
                <input asp-for="Input.Password" class="form-control" />
                <span asp-validation-for="Input.Password" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Input.ConfirmPassword"></label>
                <input asp-for="Input.ConfirmPassword" class="form-control" />
                <span asp-validation-for="Input.ConfirmPassword" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Input.UserRole"></label>
                <select asp-for="Input.UserRole" class="form-control" asp-items="ViewBag.RoleId">
                </select>
                <span asp-validation-for="Input.UserRole" class="text-danger"></span>
            </div>
            <button type="submit" class="btn btn-primary">Register</button>
        </form>
    </div>
    <div class="col-md-6 col-md-offset-2">
        <section>
            <h4>Use another service to register.</h4>
            <hr />
            @{
                if ((Model.ExternalLogins?.Count ?? 0) == 0)
                {
                    <div>
                        <p>
                            There are no external authentication services configured. See <a href="https://go.microsoft.com/fwlink/?LinkID=532715">this article</a>
                            for details on setting up this ASP.NET application to support logging in via external services.
                        </p>
                    </div>
                }
                else
                {
                    <form id="external-account" asp-page="./ExternalLogin" asp-route-returnUrl="@Model.ReturnUrl" method="post" class="form-horizontal">
                        <div>
                            <p>
                                @foreach (var provider in Model.ExternalLogins)
                                {
                                    <button type="submit" class="btn btn-primary" name="provider" value="@provider.Name" title="Log in using your @provider.DisplayName account">@provider.DisplayName</button>
                                }
                            </p>
                        </div>
                    </form>
                }
            }
        </section>
    </div>
</div>
@section Scripts {
    <partial name="_ValidationScriptsPartial" />
}

Register.cshtml.cs:

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
#nullable disable

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Text.Encodings.Web;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authorization;
using login_and_registration.Areas.Identity.Data;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Identity.UI.Services;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.AspNetCore.WebUtilities;
using Microsoft.Extensions.Logging;
using Microsoft.AspNetCore.Mvc.Rendering;

namespace login_and_registration.Areas.Identity.Pages.Account
{
    [AllowAnonymous]
    public class RegisterModel : PageModel
    {
        private readonly SignInManager<loginregistrationUser> _signInManager;
        private readonly UserManager<loginregistrationUser> _userManager;
        private readonly IUserStore<loginregistrationUser> _userStore;
        private readonly IUserEmailStore<loginregistrationUser> _emailStore;
        private readonly ILogger<RegisterModel> _logger;
        private readonly IEmailSender _emailSender;
        private readonly RoleManager<IdentityRole> _roleManager;


        public RegisterModel(
            UserManager<loginregistrationUser> userManager,
            IUserStore<loginregistrationUser> userStore,
            SignInManager<loginregistrationUser> signInManager,
            ILogger<RegisterModel> logger,
            IEmailSender emailSender,
             RoleManager<IdentityRole> roleManager)
        {
            _userManager = userManager;
            _userStore = userStore;
            _emailStore = GetEmailStore();
            _signInManager = signInManager;
            _logger = logger;
            _emailSender = emailSender;
            _roleManager = roleManager;
        }

        /// <summary>
        ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
        ///     directly from your code. This API may change or be removed in future releases.
        /// </summary>
        [BindProperty]
        public InputModel Input { get; set; }

        /// <summary>
        ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
        ///     directly from your code. This API may change or be removed in future releases.
        /// </summary>
        public string ReturnUrl { get; set; }

        /// <summary>
        ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
        ///     directly from your code. This API may change or be removed in future releases.
        /// </summary>
        public IList<AuthenticationScheme> ExternalLogins { get; set; }

        /// <summary>
        ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
        ///     directly from your code. This API may change or be removed in future releases.
        /// </summary>
        public class InputModel
        {
            /// <summary>
            ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
            ///     directly from your code. This API may change or be removed in future releases.
            /// </summary>
            /// 

            

            [Required]
            [DataType(DataType.Text)]
            [Display(Name = "First Name")]
            public string FirstName { get; set; }

            [Required]
            [DataType(DataType.Text)]
            [Display(Name = "Last Name")]
            public string LastName { get; set; }



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

            /// <summary>
            ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
            ///     directly from your code. This API may change or be removed in future releases.
            /// </summary>
            [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; }

            /// <summary>
            ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
            ///     directly from your code. This API may change or be removed in future releases.
            /// </summary>
            [DataType(DataType.Password)]
            [Display(Name = "Confirm password")]
            [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
            public string ConfirmPassword { get; set; }

            [Required]
            [Display(Name = "User Role")]
            public string UserRole { get; set; }

            [Required]
            [Display(Name = "Role")]
            public string RoleId { get; set; }
        }


        public async Task OnGetAsync(string returnUrl = null)
        {
            ReturnUrl = returnUrl;
            ExternalLogins = (await _signInManager.GetExternalAuthenticationSchemesAsync()).ToList();
        }

        public async Task<IActionResult> OnPostAsync(string returnUrl = null)
        {
            returnUrl ??= Url.Content("~/");
            var role = _roleManager.FindByIdAsync(Input.UserRole).Result;
            ExternalLogins = (await _signInManager.GetExternalAuthenticationSchemesAsync()).ToList();
            if (ModelState.IsValid)
            {
                var user = new loginregistrationUser { UserName = Input.Email, Email = Input.Email, FirstName = Input.FirstName, LastName = Input.LastName };
                 //user = CreateUser();

                await _userStore.SetUserNameAsync(user, Input.Email, CancellationToken.None);
                await _emailStore.SetEmailAsync(user, Input.Email, CancellationToken.None);
                var result = await _userManager.CreateAsync(user, Input.Password);

                if (result.Succeeded)
                {
                    _logger.LogInformation("User created a new account with password.");

                    var userId = await _userManager.GetUserIdAsync(user);
                    var code = await _userManager.GenerateEmailConfirmationTokenAsync(user);
                    code = WebEncoders.Base64UrlEncode(Encoding.UTF8.GetBytes(code));
                    var callbackUrl = Url.Page(
                        "/Account/ConfirmEmail",
                        pageHandler: null,
                        values: new { area = "Identity", userId = userId, code = code, returnUrl = returnUrl },
                        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>.");

                    if (_userManager.Options.SignIn.RequireConfirmedAccount)
                    {
                        return RedirectToPage("RegisterConfirmation", new { email = Input.Email, returnUrl = returnUrl });
                    }
                    else
                    {
                        await _signInManager.SignInAsync(user, isPersistent: false);
                        return LocalRedirect(returnUrl);
                    }
                }

                foreach (var error in result.Errors)
                {
                    ModelState.AddModelError(string.Empty, error.Description);
                }
            }


            IEnumerable<IdentityRole> roles = _roleManager.Roles.ToList();
            ViewData["RoleId"] = new SelectList(roles.ToList(), "Id", "Name");


            // If we got this far, something failed, redisplay form
            return Page();
        }

        //private loginregistrationUser CreateUser()
        //{
        //    try
        //    {
        //        return Activator.CreateInstance<loginregistrationUser>();
        //    }
        //    catch
        //    {
        //        throw new InvalidOperationException($"Can't create an instance of '{nameof(loginregistrationUser)}'. " +
        //            $"Ensure that '{nameof(loginregistrationUser)}' is not an abstract class and has a parameterless constructor, or alternatively " +
        //            $"override the register page in /Areas/Identity/Pages/Account/Register.cshtml");
        //    }
        //}

        private IUserEmailStore<loginregistrationUser> GetEmailStore()
        {
            if (!_userManager.SupportsUserEmail)
            {
                throw new NotSupportedException("The default UI requires a user store with email support.");
            }
            return (IUserEmailStore<loginregistrationUser>)_userStore;
        }
    }
}

program.cs:

using login_and_registration.Data;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using login_and_registration.Areas.Identity.Data;
using Microsoft.AspNetCore.Identity.UI.Services;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
var connectionString = builder.Configuration.GetConnectionString("lAppregistrationContextConnection");
builder.Services.AddDbContext<lAppregistrationContext>(options =>
    options.UseSqlServer(connectionString));builder.Services.AddDbContext<AppDbContext>(options =>
    options.UseSqlServer(connectionString));

builder.Services.AddDatabaseDeveloperPageExceptionFilter();

builder.Services.AddDefaultIdentity<loginregistrationUser>(options => {

    options.SignIn.RequireConfirmedAccount = false;
    options.Password.RequireLowercase = false;
    options.Password.RequireUppercase = false;
    options.Password.RequireNonAlphanumeric = false;
})
    .AddRoles<IdentityRole>()
    .AddDefaultUI()
    .AddEntityFrameworkStores<lAppregistrationContext>();
    //.AddDefaultTokenProviders();

builder.Services.AddScoped<IUserClaimsPrincipalFactory<loginregistrationUser>,ApplicationUserClaims>();

builder.Services.AddControllersWithViews();

//builder.Services.AddTransient<IEmailSender, EmailSender>();
builder.Services.AddRazorPages();
builder.Services.AddDbContext<AppDbContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("lAppregistrationContextConnection")));

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseMigrationsEndPoint();
}
else
{
    app.UseExceptionHandler("/Home/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthentication();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{


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

});

app.Run();

Answer 1

Firstly, be sure your database contains roles data in AspNetRoles table.

Then for display the dropdownlist, you also need be sure add ViewData["RoleId"] in OnGet method:

public async Task OnGetAsync(string returnUrl = null)
{
    ReturnUrl = returnUrl;
    ExternalLogins = (await _signInManager.GetExternalAuthenticationSchemesAsync()).ToList();
    IEnumerable<IdentityRole> roles = _roleManager.Roles.ToList();
    ViewData["RoleId"] = new SelectList(roles.ToList(), "Id", "Name");
}