Many-to-many relation: How is my ejb container aware of a ta

[balteo]

Hello all,

Further to several posts on this forum, I am still struggling with the same many-to-many ejb relation and before rushing into coding and possibly running into big problems I would like to understand a few points about CMR and CMP.

I have three tables (as before) which are mapped to two ejbs as follows:

*First table, called "establishments", contains two fiels "db_establishment_id" and "db_establishment_name".
Here is a sample:

db_establishment_id(pk) db_establishment_name
---------------------------------------------
1 The black frog
2 The king's head
3 McDonalds

*Second table, called "categories", contains two fields "db_category_id" and "db_category_name"
Here is a sample:

db_category_id(pk) db_category_name
-----------------------------------
1 restaurant
2 pub

*Third table, called "establishments_categories", contains two fields "db_establishment_id" and "db_id_category"
Here is a sample:

db_establishment_id(pk,fk) db_category_id(pk,fk)
--------------------------------------
1 2
2 2
2 1
3 1

These THREE tables map to TWO ejbs in a many-to-many bi-di relation.


My question is as follows:

How is my ejb container aware of a table not mentioned anywhere (here establishments_categories)? How does it update or read from this table if it is not mentioned anywhere in the DDs? Do I need to mention it in my jboss DD? Can you give me a sample of that jboss DD?

Thanks in advance,

Julien Martin.

[sesques]

Hi Julien,

In JBoss, the mapping is always done in jbosscmp-jdbc.xml
In this file, your relation should be something like;

 <ejb-relation>
 <ejb-relation-name>Etablishment-Category</ejb-relation-name>
 <relation-table-mapping>
 <table-name>establishments_categories</table-name>
 <datasource>Your data source</datasource>
 <datasource-mapping>Your data source mapping</datasource-mapping>
 <create-table>What you want</create-table>
 <remove-table>What you want</remove-table>
 </relation-table-mapping>

 <ejb-relationship-role>
 <!-- Etablishment side -->
 <ejb-relationship-role-name>Etablishment-have-Category</ejb-relationship-role-name>
 <key-fields>
 <key-field>
 <field-name>etablishment_id</field-name>
 <column-name>db_establishment_id</column-name>
 </key-field>
 </key-fields>

 </ejb-relationship-role>
 <ejb-relationship-role>
 <!-- Category side -->
 <ejb-relationship-role-name>Category-belongs-to-Etablishment</ejb-relationship-role-name>
 <key-fields>
 <key-field>
 <field-name>category_id</field-name>
 <column-name>db_category_id</column-name>
 </key-field>
 </key-fields>

 </ejb-relationship-role>
 </ejb-relation>

Something important: You must repeat the datasource and datasource mapping in the relation-table-mapping if you don't set it in the default section.

I suggest you using XDoclet to generate all the descriptors.

[balteo]

Thanks a lot for your reply Pascal,
Does Xdoclet work for ejb 2.1??
Julien.

[sesques]

Hi Julien,

The current release 1.2 (I use the beta 3 myself) NO.
EJB 2.1 will be supported by XDoclet 2 but it is not yet relased.
Check the project at:http://xdoclet.codehaus.org/

Anyway, EJB 2.1 will be supported only on JBoss 4.x.x version, which is not yet released.