Store does not implement IUserRoleStore<TUser> ASP.NET Core Identity

Question

I'm using ASP.NET Core 2.1 Identity. I've overridden IdentityUser because I need to add some additional properties on the user.

In Startup.cs

services.AddDefaultIdentity<PortalUser>().AddEntityFrameworkStores<ApplicationDbContext>();

ApplicationDbContext.cs

public partial class ApplicationDbContext : IdentityDbContext<PortalUser>
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options)
    {

    }
}

PortalUser class

public class PortalUser : IdentityUser
{
    [PersonalData]
    public DateTime? LastLoginDateUtc { get; set; }

    [PersonalData]
    public DateTime? RegistrationDateUtc { get; set; }
}

That's all working fine. I can add a user via.

_userManager.CreateAsync(user)

However, when I call AddToRolesAsync to add a role to a user, I'm getting an exception. Any ideas why?

_userManager.AddToRolesAsync(user, new List<string> { roleName });

{System.NotSupportedException: Store does not implement IUserRoleStore<TUser>.
   at Microsoft.AspNetCore.Identity.UserManager`1.GetUserRoleStore()
   at Microsoft.AspNetCore.Identity.UserManager`1.AddToRolesAsync(TUser user, IEnumerable`1 roles)}

Answer 1

In Startup.cs, I was missing AddRoles so

services.AddDefaultIdentity<PortalUser>()
    .AddEntityFrameworkStores<ApplicationDbContext>();

should be

services.AddDefaultIdentity<PortalUser>()
    .AddRoles<IdentityRole>()
    .AddEntityFrameworkStores<ApplicationDbContext>();

Note: The order is critical. AddRoles must come before AddEntityFrameworkStores