orm - Abstract class and NHibernate -

i have class:

class abstract car {     ... }  class concretecar {     ... }  class anotherconcretecar {     ... } 

yet seems confusing how map these in nhibernate. need able gather a:

list<car> cars; (car car in cars) {     ... } 

i use generator (what alternative?) generating next carid. there join-subclass, disallows that, , frankly, confusing me. seems have go making car interface, isn't want.

also, no matter method use (say make car superclass , other subclasses), if query database:

from item in session.query<car>() select item; 

will have typecast objects subclass types use subclass properties , methods? work? nhibernate figure out subclass , create objects of subclass, or create objects of superclass cannot converted subclasses?

i've implemented kind of approach while ago remember working in particular case.

i assume car base table shared columns, if map entities in following way (i'm using fluent nhibernate):

carmap:

public class carmap : classmap<car> { ... } 

concretecarmap:

public class concretecarmap : subclassmap<concretecar> {     public concretecarmap()     {         extends<carmap>();          // other properties         // map(x => x.property).not.nullable();     } } 

having execute query:

from item in session.query<car>() select item; 

and indeed have typecast returned objects subclass types in order access subclass properties , methods nhibernate intelligent enough construct them you.

nhibernate achieve using kind of syntax (pseudo sql):

select  -- columns car -- columns concretecar  -- other columns subclasses  case      when f1.subid not null 1     when f2.subid not null 2     when f3.subid not null 3     when f4.subid not null 4     when f5.subid not null 5     when f0.id not null 0 end type  car f0 left outer join concretecar f1 on f0.id = f1.subid -- other joins 

so depending on actual number of implemented subclasses can have impact on performance.

i hope answers question.