Hi folks,

I have been driving myself crazy trying to get a many-to-many mapping to work properly and I am hoping that it is something simple!

I have three tables:
1) accomodation
2) accomodation_electronic
3) contact_electronic

accomodation_electronic is the table that joins accomodation and contact_electronic - it simply holds foreign keys to both tables.

In the code snippet below I load an existing accomodation, create a new electronic and add it to the Set of existing electronic addresses. The code runs with no exceptions but unfortunately the only table that is touched is contact_electronic.

By watching the SQL calls I can see that a new row is added to contact_electronic but no row is added in accomodation_electronic - there is nothing to link the newly added contact_electronic with the accomodation.

I could remove the link table and create a one-to-many but I intend to use contact_electronic for other electronic addresses as well e.g., employee emails, company websites etc so it would be great if I can get this many-to-many to work.

My mappings are as follows:

--------------------------------------------------------------------------------
| accomodation.hbm.xml
--------------------------------------------------------------------------------
<class name="Accomodation" table="accomodation">

<jcs-cache usage="nonstrict-read-write"/>

<id name="id" type="java.lang.Long" unsaved-value="null">
<column name="accomodation_ser" sql-type="integer" not-null="true"/>
<generator class="sequence">
<param name="sequence">accomodation_accomodation_ser_seq</param>
</generator>
</id>

<set name="electronicAddresses" lazy="false" table="accomodation_electronic" sort="natural" inverse="true">
<jcs-cache usage="nonstrict-read-write"/>
<key column="accomodation_ser"/>
<many-to-many class="Electronic" column="contact_electronic_ser"/>
</set>
</class>
--------------------------------------------------------------------------------



--------------------------------------------------------------------------------
| electronic.hbm.xml
--------------------------------------------------------------------------------
<class name="Electronic" table="contact_electronic">

<jcs-cache usage="nonstrict-read-write"/>

<id name="id" type="java.lang.Long" unsaved-value="null">
<column name="contact_electronic_ser" sql-type="integer" not-null="true"/>
<generator class="sequence">
<param name="sequence">contact_electronic_contact_electronic_ser_seq</param>
</generator>
</id>

<property name="electronicType" type="java.lang.Character">
<column name="contact_type_code" sql-type="char(1)" not-null="true"/>
</property>

<property name="lastModifiedByUserId" type="java.lang.Long">
<column name="last_modified_by" sql-type="integer" not-null="true"/>
</property>

</class>
--------------------------------------------------------------------------------

Note that there is no mapping back to accomodation from electronic... I am not sure if this is required; still getting my feet wet :)



--------------------------------------------------------------------------------
| Finally, the code:
--------------------------------------------------------------------------------
...
Transaction tx = null;

try
{
Session session = getSessionFactory().openSession();
Accomodation a = (Accomodation) session.load (Accomodation.class, new Long (1));

tx = session.beginTransaction();

Electronic e = new Electronic ();
e.setLastModifiedByUserId(new Long(1));
e.setElectronicType(new Character ('W'));

session.save(getElectronic());

a.getElectronicAddresses().add(e);

session.saveOrUpdate(a);

session.flush();

tx.commit();
}
...
--------------------------------------------------------------------------------


Thanks in advance to anyone who can offer any assistance - I am really enjoying Hibernate and want to keep learning!

Kind regards,

Damian

OK... I found the problem and am kicking myself (quite hard). The troublemaker was a compareTo method in the Electronic class - once I removed this method everything fell into place quite nicely.

I read in another post that I can reinstate the compareTo method and feel safe that it won't throw NullPointerExceptions as long as I set lazy="true" for the <set>. Will probably end up adding a column to the join table instead (more learning fun!)