DataNucleus is developed as a plugin-driven framework and one of the components that is pluggable is the support for JDOQL/JPQL expressions for java types in the "new" query mechanism. When you add support for a new java type, if you want to query fields of that type you will need to provide this.
While you can define details of how your type is queryable, we only document here what you would do for a type that is mapped to a String (since that's the most common use-case). Here you simply need to add an entry into plugin.xml defining which expression and literal class you would use for handling that type.
Say we have a java type that is mapped using mydomain.MyTypeMapping. Simply add a file plugin.xml to your JAR at the root, and it should look like this
<?xml version="1.0"?> <plugin id="mydomain" name="DataNucleus plug-ins" provider-name="My Company"> <extension point="org.datanucleus.store.rdbms.sql_expression"> <sql-expression mapping-class="mydomain.MyTypeMapping" literal-class="org.datanucleus.store.rdbms.sql.expression.StringLiteral" expression-class="org.datanucleus.store.rdbms.sql.expression.StringExpression"/> </extension> </plugin>
Note that you also require a MANIFEST.MF file as per the Plugins Guide.