Question

I have an entity class which has 3 columns; entityType, entityID and EntityText. I want to fill entityText column from 3 conditional tables.For example: If entity type is 3(contact) and entityID is 2 it will join to Contacts table and will get the contact by entityID and set contact.name property as EntityText. How can I do this?

Details:
Not same object class.

Contact
{
contactID
firstName
lastName
..
}
Company
{
companyID
name
address
...
}
 Task{
taskID
entityID
entityType
entityText= Company.name or Contact.firstName + Contact.lastName
...
}

Answer 1

EDIT: refactored to match the updated question

because there is logic behind the content of EntityText i would prefere polymorphism

public abstract class Task
{
    public virtual int Id { get; set; }
    public abstract string Text { get; set; }
}

public class ContactTask : Task
{
    public virtual Contact Contact { get; set; }
    public override string Text
    {
        get { return Contact.FirstName + " " + Contact.LastName; }
        set { Contact.FirstName = value.Split(' ')[0]; Contact.LastName = value.Split(' ')[1]; }
    }
}
public class CompanyTask : Task
{
    public virtual Company Company { get; set; }
    public override string Text
    {
        get { return Company.Name; }
        set { Company.Name = value; }
    }
}

public class TaskMap : ClassMap<Task>
{
    public TaskMap()
    {
        Table("TaskTable");

        Id(c => c.Id, "taskID").GeneratedBy....();
        DiscriminateSubclassesOn("entityType");
    }
}

public class ContactTaskMap : ClassMap<ContactTask>
{
    public ContactTaskMap()
    {
        DiscriminatorValue(3);
        References(ct => ct.Contact, "entityID");
    }
}

public class CompanyTaskMap : ClassMap<CompanyTask>
{
    public ContactTaskMap()
    {
        DiscriminatorValue(2);
        References(ct => ct.Company, "entityID");
    }
}

// get all tasks
var all = session.QueryOver<Task>().List();

// get all tasks for Company
var companyTasks = session.QueryOver<CompanyTask>().List();