Mapping person and employee in Fluent NHibernate

Question

How can I map following queries using Fluent NHibernate (entity, mapping class etc..), the employee ids are stored in identifier tables. Person table contains employee information and non-employee information.

SELECT p.Id, p.FirstName, p.LastName

 FROM Person p  

UNION ALL

SELECT e.Id, e.FirstName, e.LastName 

  FROM Employee e 

INNER JOIN identifier i on (e.Id = i.value)

INNER JOIN type t on (i.typeid = t.id and i.typeName = 'EmployeeId')

Anyone?

Answer 1

You need to use a union strategy for mapping your subclasses. Have a read of the subclassing section of the Fluent NHibernate wiki, but instead of calling DiscriminateSubclassesOnColumn in your ClassMap you'd call UseUnionSubclassForInheritanceMapping.

What you'd end up with is a ClassMap for your base-class, then a SubclassMap for each of your subclasses; the ClassMap would have a call to UseUnionSubclassForInheritanceMapping in it's constructor.

Something like this:

public class PersonMap : ClassMap<Person>
{
  public PersonMap()
  {
     // ... mappings ...
     UseUnionSubclassForInheritanceMapping();
  }
}

public class EmployeeMap : SubclassMap<Employee>
{
  public EmployeeMap()
  {
    // ... mappings ...
  }
}