public async Task AddToRoleAsync(T user, string roleName)
{
if (user == null)
{
throw new ArgumentNullException("user", "Parameter user cannot be null.");
}
if (string.IsNullOrEmpty(roleName))
{
throw new ArgumentNullException("roleName", "Parameter roleName cannot be null.");
}
var roleId = await _roleTable.GetRoleIdAsync(roleName);
if (roleId != null)
{
await _userRolesTable.AddUserToRoleAsync(user, (string)roleId);
}
}