very shortened :

public class Contractor extends Persistent {
   /**
    * @hibernate.set lazy="true" inverse="true" cascade="all"
    * @hibernate.collection-key column="contractor"
    * @hibernate.collection-one-to-many class="com.xxx.model.Region"
    */
   public Set getRegions() {
      return regions;
   }
}

public class Region extends Persistent implements Comparable {
   /**
    * @hibernate.set
    *      lazy="true"
    *      cascade="none"
    *       table="Region2Depot"
    * @hibernate.collection-key
    *      column = "region"
    * @hibernate.collection-many-to-many
    *      column="depot"
    *      class = "com.xxx.model.Depot"
    */
   public Set getDepots() {
      return depots;
   }
}

public class Net extends Persistent {
   /**
    * @hibernate.set lazy="true" inverse="true" cascade="all"
    * @hibernate.collection-key column="net"
    * @hibernate.collection-one-to-many class="com.xxx.model.Depot"
    */
   public Set getDepots() {
      return depots;
   }
}

public class Depot extends Persistent implements Comparable {
   /**
    * @hibernate.many-to-one not-null="true"
    * @return
    */
   public Net getNet() {
      return net;
   }

   public void setNet( Net net ) {
      this.net = net;
   }
}

private static void processLine( String str, Session session, Contractor cnt ) {
    String[] temp = str.split( ";" );

    String number = temp[ 0 ];
    String netName = temp[ 1 ];
    String city = temp[ 2 ];
    String street = temp[ 3 ];
    String buildingNumber = temp[ 4 ];
    String appartmentNumber = temp[ 5 ];
    String postalCode = temp[ 6 ];
    String regionName = temp[ 7 ];

    try {
        Transaction tx = session.beginTransaction();

        Net net = null;
        Region region = null;

        List regions = session.find(    "from Region r where r.name = ?",
                                        regionName,
                                        Hibernate.STRING );

        if ( !regions.isEmpty() ) {
            region = (Region) regions.get( 0 );
        } else {
            region = new Region( regionName );
            region.setContractor( cnt );
            session.save( region );
        }

        List nets = session.find(   "from Net n where n.name = ?",
                                    netName,
                                    Hibernate.STRING );
        if ( !nets.isEmpty() ) {
            net = (Net) nets.get( 0 );
        } else {
            net = new Net( netName );
            session.save( net );
        }

        Depot depot = null;
        Address address = new Address( city, postalCode, street, buildingNumber,
                        appartmentNumber );
        session.save( address );
        depot = new Depot( city );
       
        depot.setAddress( address );
        net.addDepot( depot );
       
        session.save( depot );
        session.saveOrUpdate( net );
        region.addDepot( depot );
        session.saveOrUpdate( region );
        tx.commit();
       
        // PROBLEM !!!
        //session.evict( region );
    } catch ( HibernateException e1 ) {
        e1.printStackTrace();
    }

}

Net net = new Net( "net" );
Depot depot1 = new Depot( net, "depot1" );
Depot depot2 = new Depot( net, "depot2" );
Set set = new TreeSet();

set.add( depot1 );
set.add( depot2 );

System.out.println( set.size() );

public int compareTo( Object object ) {
    Depot depot = (Depot) object;
    return new CompareToBuilder().append(   this.name,
                                            depot.getName() )
                                 .append(   this.getId(),
                                            depot.getId() )
                                 .append(   this.hashCode(),
                                            depot.hashCode() ).toComparison();
}