public class CompanyDTO implements Serializable{

   private static final long serialVersionUID = 1L;

   private Long company_id;

   private String name;
   
   private EmployeeDTO employee;
   
   private String position;
   
   private Long employeeId;

      ............(getters-setters).............

}

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
   <class name="CompanyDTO" table="COMPANY" lazy="false"
      batch-size="100">
      <id name="company_id" column="COMPANY_ID" type="java.lang.Long">
         <generator class="native" />
      </id>

      <property name="name" column="NAME" type="string" />

   

      <property name="employeeId" />
   

      <set name="address_fk" table="COMP_ADR" fetch="join">
         <key column="company_id" />
         <many-to-many column="ADDRESS_ID" class="AddressDTO" />
      </set>

      <property name="counEmplForCompany"
         formula="(select count(*) from COMP_EMPL s where company_id = s.COMPANY_ID )" />
      
      
   <join table="COMP_EMPL" inverse="true" optional="true">
         <key column="company_id" />
         <many-to-one name="employee" column="employee_id" not-null="true" />
         
         <property name="position" type="string"
         formula="(select distinct ce.position FROM COMP_EMPL ce WHERE company_id=ce.COMPANY_ID and ce.employee_id=[b]employee_id[/b])" />
         
         
      </join>


   </class>
</hibernate-mapping>