I am using mysql. I have the follwing mapping file. Here FullArticle extends from Article. Also FullArticle has a collection of authors which are mapped using composite element.
When I load FullArticle and do a
Collection authors = fullArticle.getAuthors(), null value for authors is returned

<class name="org.bsms.persistence.jdo.Article" table="article" proxy="org.bsms.persistence.jdo.Article">
<id name="id" column="article_id" type="java.lang.Long" unsaved-value="null">
<generator class="native">
<param name="native">article_seq</param>
</generator>
</id>
<property name="subject" column="subject" type="string"/>
<many-to-one name="type" column="article_type_id" class="org.bsms.persistence.jdo.ArticleType"/>
<property name="wordCount" column="word_count" type="integer"/>
.....
<many-to-one name="journal" column="journal_id" class="org.bsms.persistence.jdo.JournalJDO" cascade="none" outer-join="false"/>

<joined-subclass name="org.bsms.persistence.jdo.FullArticle" table="full_article" proxy="org.bsms.persistence.jdo.FullArticle">
<key column="full_article_id"/>
<property name="keyWords" column="keyWords" type="string"/>
<bag name="authors" table="author" lazy="true">
<key column="full_article_id"/>
<composite-element class="org.bsms.persistence.jdo.AuthorJDO">
<property name="firstName" column="first_name" type="string"/>
<property name="surName" column="sur_name" type="string"/>
</composite-element>
</bag>
<many-to-one name="category" column="category_id" class="org.bsms.persistence.jdo.ArticleCategory" cascade="none" outer-join="false"/>
</joined-subclass>

</class>

Check your getters and setters.

as per the forum entrance


It's hard to do divination.