help with non decomposed M:N

Hello everyone,

I've been trying to use OJB lately but I'm a newbie and I'm stuck with 
handling simple non decomposed M:N relationships.

Here's my purpose :

A <- m:n -> B
A <- m:n -> C

*** Mapping is :

<class-descriptor class="my.test.business.A"
    table="TBLA">
    <field-descriptor name="id" column="ID" jdbc-type="BIGINT"
        nullable="false" indexed="true" primarykey="true"
        autoincrement="true">
    </field-descriptor>
    <field-descriptor name="att1" column="ATT1" jdbc-type="BIGINT" 
nullable="false" indexed="true">
    </field-descriptor>
    <field-descriptor name="att2" column="ATT2" jdbc-type="VARCHAR" 
nullable="true" indexed="false">
    </field-descriptor>
    <collection-descriptor name="bs" 
collection-class="org.apache.ojb.broker.util.collections.ManageableArrayList" 

        element-class="my.test.business.B"
        auto-retrieve="false" auto-update="link"
        indirection-table="TBLAB">
        <fk-pointing-to-this-class column="A_ID" />
        <fk-pointing-to-element-class column="B_ID" />
    </collection-descriptor>
    <collection-descriptor name="cs" 
collection-class="org.apache.ojb.broker.util.collections.ManageableArrayList" 

        element-class="my.test.business.C"
        auto-retrieve="false" auto-update="link"
        indirection-table="TBLAC">
        <fk-pointing-to-this-class column="A_ID" />
        <fk-pointing-to-element-class column="C_ID" />
    </collection-descriptor>
</class-descriptor>

<class-descriptor class="my.test.business.B"
    table="TBLB">
    <field-descriptor name="id" column="ID" jdbc-type="BIGINT"
        nullable="false" indexed="true" primarykey="true"
        autoincrement="true">
    </field-descriptor>
    <field-descriptor name="label" column="LABEL"
        jdbc-type="VARCHAR" nullable="false" indexed="false">
    </field-descriptor>
    <collection-descriptor name="as"
     
collection-class="org.apache.ojb.broker.util.collections.ManageableArrayList" 

        element-class="my.test.business.A"
        auto-retrieve="false" auto-update="link"
        indirection-table="TBLAB">
        <fk-pointing-to-this-class column="B_ID" />
        <fk-pointing-to-element-class column="A_ID" />
    </collection-descriptor>
</class-descriptor>

<class-descriptor class="my.test.business.C"
    table="TBLC">
    <field-descriptor name="id" column="ID" jdbc-type="BIGINT"
        nullable="false" indexed="true" primarykey="true"
        autoincrement="true">
    </field-descriptor>
    <field-descriptor name="label" column="LABEL"
        jdbc-type="VARCHAR" nullable="false" indexed="false">
    </field-descriptor>
    <collection-descriptor name="as"
     
collection-class="org.apache.ojb.broker.util.collections.ManageableArrayList" 

        element-class="my.test.business.A"
        auto-retrieve="false" auto-update="link"
        indirection-table="TBLAC">
        <fk-pointing-to-this-class column="C_ID" />
        <fk-pointing-to-element-class column="A_ID" />
    </collection-descriptor>
</class-descriptor>

*** DDL is :

CREATE TABLE SEQ (
  TABLENAME varchar(250) NOT NULL,
  MAX_KEY bigint(20) default NULL,
  GRAB_SIZE int(11) default NULL,
  VERSION int(11) default NULL,
  PRIMARY KEY  (TABLENAME)
)

CREATE TABLE TBLA (
  ID bigint(20) unsigned NOT NULL auto_increment,
  ATT1 bigint(20) unsigned NOT NULL default '0',
  ATT2 varchar(255) default NULL,
  PRIMARY KEY  (ID)
)

CREATE TABLE TBLB (
  ID bigint(20) unsigned NOT NULL auto_increment,
  LABEL varchar(255) default NULL,
  PRIMARY KEY  (ID)
)

CREATE TABLE TBLC (
  ID bigint(20) unsigned NOT NULL auto_increment,
  LABEL varchar(255) default NULL,
  PRIMARY KEY  (ID)
)

CREATE TABLE TBLAB (
  A_ID bigint(20) unsigned NOT NULL default '0',
  B_ID bigint(20) unsigned NOT NULL default '0',
  PRIMARY KEY (A_ID,B_ID),
  CONSTRAINT FKAB1 FOREIGN KEY (A_ID) REFERENCES A (ID),
  CONSTRAINT FKAB2 FOREIGN KEY (B_ID) REFERENCES B (ID)
)

CREATE TABLE TBLAC (
  A_ID bigint(20) unsigned NOT NULL default '0',
  C_ID bigint(20) unsigned NOT NULL default '0',
  PRIMARY KEY (A_ID,C_ID),
  CONSTRAINT FKAC1 FOREIGN KEY (A_ID) REFERENCES A (ID),
  CONSTRAINT FKAC2 FOREIGN KEY (C_ID) REFERENCES C (ID)
)

*** and code is :

public class A implements Serializable {
  private Long id;
  private Long att1;
  private String att2;
  private List bs = new ArrayList();
  private List cs = new ArrayList();
  /* and getters/setters */
}

public class B implements Serializable {
  private Long id;
  private String label;
  private List as = new ArrayList();
  /* and getters/setters */
}

public class C implements Serializable {
  private Long id;
  private String label;
  private List as = new ArrayList();
  /* and getters/setters */
}

***

You might have noticed the collections auto-retrieve setting is set to 
'false'. If I set this setting to true in *A* class mapping, I get a 
NullPointerException when I try to read instances of A.

Furthermore, auto-retrieve set to false, I can read and add new objects 
but I also get NullPointerExceptions when trying to update an object 
already stored.

Is there anything I'm doing wrong ? Please, do not hesitate to ask me 
questions. Any help would be greatly appreciated.

Many thanks.
Ramzi Oueslati