<class name="mypack.OrganizationalUnit" table="RH_OUNIT" lazy="false">
  <id name="id">
   <column name="OUNIT_ID" not-null="true" unique="true" sql-type="NUMBER"/>
      <generator class="sequence">
       <param name="sequence">RH_GENERIC_SEQ</param>
      </generator>
  </id>
   <property name="key" column="OUNIT_KEY" type="string" not-null="false"/>
   <property name="nameFr" column="OUNIT_NAME_FR" type="string" not-null="false"/>
   <property name="nameNl" column="OUNIT_NAME_NL" type="string" not-null="false"/>
    <set name="members" table="RH_EMP_OUNIT_LINK" cascade="all">
      <key column="OUNIT_ID" not-null="true"/>
       <many-to-many class="mypack.Employee" column="EMP_ID"/>
   </set>
</class>

public class OrganizationalUnit {

    private long id;
    private String nameFr;
    private String nameNl;
    private String key;
    private Set members = new HashSet();
    public long getId() {
        return id;
    }
    public void setId(long id) {
        this.id = id;
    }
    // ......
    public Set getMembers() {
        return members;
    }
    public void setMembers(Set members) {
        this.members = members;
    }
}

//Get an "Employee", get an OrganziationUnit by id,
// content of both objects show datas comes from database (ie not empty new objects)
ounit.getMembers().add(newEmployee);
Transaction tx = session.beginTransaction();
session.update(ounit);
tx.commit();
//Note: using long running session in webapp environnment, session is associated with requesting user and reattached each time. That explain why you don't see the load() codes.

Hibernate: select organizati0_.OUNIT_ID as OUNIT1_, organizati0_.OUNIT_KEY as OUNIT2_37_, organizati0_.OUNIT_NAME_FR as OUNIT3_37_, organizati0_.OUNIT_NAME_NL as OUNIT4_37_ from RH_OUNIT organizati0_

package com.examscam.mappings;
import java.util.*;
import javax.persistence.*;

@Entity
public class LeftManyStudent {

  long id;
  String studentName;
  List<RightManyCourse> courses = new Vector();


  @ManyToMany
  @JoinTable(name = "join_table",
joinColumns = { @JoinColumn(name = "lmstudent_id")},
inverseJoinColumns={@JoinColumn(name="rmcourse_id")}   
  )
  public List<RightManyCourse> getCourses(){
    return courses;
  }
  public void setCourses(List<RightManyCourse> righties){
    this.courses = righties;
  }

  @Id
  @GeneratedValue
  public long getId() {return id;}
  public void setId(long id) {this.id = id;}

  public String getStudentName() {
    return studentName;
  }
  public void setStudentName(String s){
    studentName=s;
  }

}

package com.examscam.mappings;

import java.util.*;
import javax.persistence.*;

@Entity
public class RightManyCourse {
  long id;
  String courseCode;
  List<LeftManyStudent> students = new Vector();

@ManyToMany
@JoinTable(name = "join_table",
joinColumns={@JoinColumn(name="rmcourse_id")},
inverseJoinColumns={@JoinColumn(name="lmstudent_id")})
  public List<LeftManyStudent> getStudents() {
    return students;
  }
  public void setStudents(List<LeftManyStudent> lefties){
    this.students = lefties;
  }

  @Id
  @GeneratedValue
  public long getId() {
    return id;
  }
  public void setId(long id) {
    this.id = id;
  }

  public String getCourseCode() {
    return courseCode;
  }
  public void setCourseCode(String courseCode) {
    this.courseCode = courseCode;
  }

}

public static void main (String args[]) {
HibernateUtil.recreateDatabase();

  LeftManyStudent student01 = new LeftManyStudent();
  student01.setStudentName("Jim Jump");
  LeftManyStudent student02 = new LeftManyStudent();
  student02.setStudentName("Julie Camp");
  LeftManyStudent student03 = new LeftManyStudent();
  student03.setStudentName("Cam Johnson");
  LeftManyStudent student04 = new LeftManyStudent();
  student04.setStudentName("Marcus McKenzie");
  RightManyCourse java101 = new RightManyCourse();
  java101.setCourseCode("Java-101");
  RightManyCourse cplus101 = new RightManyCourse();
  cplus101.setCourseCode("C++ - 101");
  RightManyCourse math101 = new RightManyCourse();
  math101.setCourseCode("Math - 101");

  java101.getStudents().add(student01);
  java101.getStudents().add(student02);
  java101.getStudents().add(student03);
  cplus101.getStudents().add(student02);
  cplus101.getStudents().add(student03);
  math101.getStudents().add(student04);

  Session session = HibernateUtil.beginTransaction();
  session.save(student01);
  session.save(student02);
  session.save(student03);
  session.save(student04);
  session.save(java101);
  session.save(cplus101);
  session.save(math101);
  HibernateUtil.commitTransaction();
}