Is it possible to create indices on join table using Hibernate annotations and hbm2ddl?

Question

I have a two entities in many-to-many association. Hibernate creates a join table for this association if hbm2ddl is activated. However, since I do not have an entity for this table, I can not apply @Index annotation. Is there a way to tell hibernate hbm2ddl to generate indices and primary key on the join table?

Answer 1

Hi Dan. One option is to use auxiliary database objects, but it would require you to switch from JPA annotations to a traditional .hbm.xml file.

Here is an example:

<!-- class mapping: -->
<class name="Entity1" table="Entity1">

  <!-- insert other mappings here -->

  <!-- this class's half of the many-to-many relationship: -->
  <set name="Entity2s" table="TheJoinTable">
    <key column="Entity1ID" />
    <many-to-many class="Entity2" column="Entity2ID" />
  </set>
</class>

<!-- auxiliary object: -->
<database-object>
  <create>CREATE INDEX MyIndex ON TheJoinTable(Entity1ID)</create>
</database-object>

Another option is to just bite the bullet and create a full-fledged entity to replace the join table. This is in fact what I did in a similar situation.

Hope this helps.