使用NHibernate时如何处理成员资格/角色？

public enum Role
{
    Member,
    Admin,
    SuperAdmin
}

public class RoleUserType : IUserType
{
    public new bool Equals(object x, object y)
    {
        if (ReferenceEquals(x, y)) return true;
        if (x == null || y == null) return false;
        return x.Equals(y);
    }

    public int GetHashCode(object x)
    {
        return x.GetHashCode();
    }

    public object NullSafeGet(IDataReader rs, string[] names, object owner)
    {
        int index = rs.GetOrdinal(names[0]);
        if (rs.IsDBNull(index)) return null;
        return (Role)Enum.Parse(typeof(Role), rs.GetString(index));
    }

    public void NullSafeSet(IDbCommand cmd, object value, int index)
    {
        if (value == null)
        {
            ((IDataParameter)cmd.Parameters[index]).Value = DBNull.Value;
        }
        else
        {
            ((IDataParameter)cmd.Parameters[index]).Value = value.ToString();
        }
    }

    public object DeepCopy(object value)
    {
        return value;
    }

    public object Replace(object original, object target, object owner)
    {
        return original;
    }

    public object Assemble(object cached, object owner)
    {
        return cached;
    }

    public object Disassemble(object value)
    {
        return value;
    }

    public SqlType[] SqlTypes => new[] { SqlTypeFactory.GetSqlType(DbType.String) };

    public Type ReturnedType => typeof(Role);

    public bool IsMutable => false;
}

public class User
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual string Email { get; set; }
    public virtual Role Role { get; set; }
}