NHibernate - 将同一实体映射到同一数据库中的不同表

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

public class FullTimeEmployee : Employee
{
    public virtual decimal Salary { get; set; }
}

public class PartTimeEmployee : Employee
{
    public virtual decimal HourlyRate { get; set; }
}

public class EmployeeMap : ClassMap<Employee>
{
    public EmployeeMap()
    {
        Id(x => x.Id);
        Map(x => x.Name);
        Map(x => x.Email);
        DiscriminateSubClassesOnColumn("employee_type");
    }
}

public class FullTimeEmployeeMap : SubclassMap<FullTimeEmployee>
{
    public FullTimeEmployeeMap()
    {
        DiscriminatorValue("full_time");
        Map(x => x.Salary);
    }
}

public class PartTimeEmployeeMap : SubclassMap<PartTimeEmployee>
{
    public PartTimeEmployeeMap()
    {
        DiscriminatorValue("part_time");
        Map(x => x.HourlyRate);
    }
}