Inheritance with NHibernate mapping and Abstract class

Question

I am trying to map an class which two other classes will inherit from, i wish to make it abstract so i will be able to return a list which containing two type of child object and cast them accordingly with a discriminator in the parent class.

For an example of my codes, BD looks like the following:

Here are my Domain models:

public class Person
{
    public int id {get; set;}
    public string name{get; set;}
}

public class Teacher : Person
{
    public string subject{get; set;}
}

public class Student : Person
{
    public string grade{get; set;}
}

And my Nhibernate mapping:

<?xml version="1.0" encoding="utf-8"?>
<hibernate-mapping namespace="Domain.Model" assembly="Domain" xmlns="urn:nhibernate-mapping-2.2" auto-import="false">
    <class name="Person" table="`Person`" schema="`PR`">
        <id name="id" access="property" column="`id`">
            <generator class="identity"/>
        </id>

        <property name="id" type="int" column="`id`" />
        <property name="name" type="String" column="`name`" />

        <joined-subclass name="Teacher" table="`Teacher`" schema="`PR`">
            <key column="`id`" />
            <property name="subject" type="String" column="`subject`" />
        </joined-subclass>
        <joined-subclass name="Student" table="`Student`" schema="`PR`">
            <key column="`id`" />
            <property name="grade" type="String" column="`grade`" />
        </joined-subclass>
    </class>
</hibernate-mapping>

I wish to make my "Person" class abstract so I will be able to have a list that can contain both child type but I'm not sure how to do it

Answer 1

Polymorphism does not require the base class to be abstract. You can work on a List<Person> containing Teacher and Student instances without having Person being abstract.

Setting Person as abstract in code only forbid to create a Person instance.

Setting Person as abstract in NHibernate mapping with a 'table per subclass' model tells to NHibernate that the Person table must have a corresponding entry in one of the subclass table. If your DB contain some rows in Person without any corresponding row in Student or Teacher , then this is an error.

Maybe this blog could help better understand what you should do.