如何显示具有角色的用户列表-ASP.NET（核心）

根据您的代码，似乎您正在使用具有自定义自定义用户数据和角色的Asp.net Core Identity。

首先，请检查Startup.ConfigureServices方法，确保已将角色添加到ApplicationUser。像这样：

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<ApplicationDbContext>(options =>
            options.UseSqlServer(
                Configuration.GetConnectionString("DefaultConnection")));

        services.AddIdentity<ApplicationUser, IdentityRole>(options => options.SignIn.RequireConfirmedAccount = true)
                 .AddDefaultUI()
                 .AddEntityFrameworkStores<ApplicationDbContext>()
                 .AddDefaultTokenProviders();

        //or using the following code.
        //services.AddDefaultIdentity<ApplicationUser>(options => options.SignIn.RequireConfirmedAccount = true)
        //    .AddRoles<IdentityRole>()
        //    .AddEntityFrameworkStores<ApplicationDbContext>();

        services.AddControllersWithViews();
        services.AddRazorPages();

    }

您可以参考本文，以了解如何添加具有asp.net Core身份的角色。

然后，在控制器中，可以使用UserManager.GetRolesAsync方法获取指定用户所属的角色名称的列表。像这样的代码：

public class ApplicationUserController : Controller
{
    private readonly UserManager<ApplicationUser> _userManager;

    private readonly ApplicationDbContext _context;
    public ApplicationUserController(UserManager<ApplicationUser> usermanager, ApplicationDbContext context)
    {
        _userManager = usermanager;
        _context = context;
    }
    public IActionResult Index()
    {
        var users = _userManager.Users.Select(c => new UsersViewModel()
        {
            Username = c.UserName,
            Email = c.Email,
            Role = string.Join(",", _userManager.GetRolesAsync(c).Result.ToArray())
        }).ToList();

        return View(users);
    }
}

结果如下：

此外，在使用Asp.net标识时，数据库将使用AspNetUserRoles表存储AspNetUsers表和AspNetRoles表之间的关系（可以使用SQL Server Management Studio来检查数据库表）。如果您不想使用UserManager来获取用户的角色，则可以加入AspNetUsers，AspNetUserRoles和AspNetRoles表并查询数据库并获取所需的属性。代码如下：

public class ApplicationUserController : Controller
{
    private readonly UserManager<ApplicationUser> _userManager;

    private readonly ApplicationDbContext _context;
    public ApplicationUserController(UserManager<ApplicationUser> usermanager, ApplicationDbContext context)
    {
        _userManager = usermanager;
        _context = context;
    }
    public IActionResult Index()
    { 
        var result = _context.Users
            .Join(_context.UserRoles, u => u.Id, ur => ur.UserId, (u, ur) => new { u, ur })
            .Join(_context.Roles, ur => ur.ur.RoleId, r => r.Id, (ur, r) => new { ur, r }) 
            .Select(c => new UsersViewModel()
            {
                Username = c.ur.u.UserName,
                Email = c.ur.u.Email,
                Role = c.r.Name
            }).ToList().GroupBy(uv=> new { uv.Username, uv.Email }).Select(r=> new UsersViewModel()
            {
                Username = r.Key.Username,
                Email = r.Key.Email,
                Role = string.Join(",", r.Select(c=>c.Role).ToArray())
            }).ToList();

        // you could also use the following code:
        var result2 = _context.Users
        .Join(_context.UserRoles, u => u.Id, ur => ur.UserId, (u, ur) => new { u, ur })
        .Join(_context.Roles, ur => ur.ur.RoleId, r => r.Id, (ur, r) => new { ur, r })
        .ToList()
        .GroupBy(uv => new { uv.ur.u.UserName, uv.ur.u.Email }).Select(r => new UsersViewModel()
        {
            Username = r.Key.UserName,
            Email = r.Key.Email,
            Role = string.Join(",", r.Select(c => c.r.Name).ToArray())
        }).ToList();

        return View(result);
    }
}

通过使用上面的linq命令，我们也可以获得相同的结果。

额外资源：

Db上下文：

public class ApplicationDbContext : IdentityDbContext
{
    public DbSet<ApplicationUser> ApplicationUsers { get; set; }
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }
    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
    }
}

public class ApplicationUser: IdentityUser
{
    public int Age { get; set; }
    public string CustomTag { get; set; }
}