c# - How to retrieve parent objects without children -

i have parent class person , child class employee parent class manager

class person {     private int _personid;     private string _fullname;     ....     .... }  class employee : person {     private int _salary;     ....     .... }  class manager : employee {     private project _project;     ....     .... } 

now, need employees without managers. tried:

var employees = employee e in db                 select e; 

but noticed have managers inside collection because of inheritance. thought this:

var employees = employee e in db                 manager m in db                 e.personid != m.personid                 select e; 

but donэt have managers inside collection have twice same information in collection because of inheritance. need parents without children.

i using db4o object database , not familiar linq.

update:

embeddedobjectcontainer db = db4oembedded.openfile(path_to_database); 

i figured out how this, have query twice not best solution.

var employees = employee e in db                 select e;  var managers = manager m in db                select m;  var result = employees.except(managers); 

i not familiar db4o nor db4o linq implementation, standard linq should work:

var employees = db.asqueryable<employee>().where(e => !(e manager));