ASP.NET Core Razor Post "Value" and "Text" from ddl

Question

I want to update User Roles by using a select and post it to db. The select is working fine for RoleName but when I change or add a role, the RoleId has to be updated too. How do I do that in Razor pages?

With the below code only the RoleName is updated, for RoleId I get error because its valuue is null 

 

UserRoleClassName = await _context.Roles.Select(a => new SelectListItem
                                                        {
                                                            Value = a.Id.ToString(),
                                                            Text = a.Name
                                                        }).ToListAsync();

<div class="col-3">
                <label for="RoleName">Role Name</label>
                <select name="Role" class="form-control" asp-for="AppIdentityRole.Role" asp-items="Model.UserRoleClassName"></select>
            </div>
            <input hidden name="RoleId" asp-for="AppIdentityRole.RoleId" class="form-control" value="@Model.UserRoleClassName" />