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Every select or finder method (except findByPrimaryKey
) must have an EJB-QL query defined in the ejb-jar.xml
file. The EJB-QL query is declared in a query element, which is contained in the entity element. The following are the declarations for findBadDudes_ejbql
and ejbSelectBoss_ejbql
queries:
<ejb-jar> <enterprise-beans> <entity> <ejb-name>GangsterEJB</ejb-name> <!-- ... --> <query> <query-method> <method-name> findBadDudes_ejbql </method-name> <method-params> <method-param>int</method-param> </method-params> </query-method> <ejb-ql><![CDATA[ SELECT OBJECT(g) FROM gangster g WHERE g.badness > ?1 ]]></ejb-ql> </query> <query> <query-method> <method-name> ejbSelectBoss_ejbql </method-name> <method-params> <method-param>java.lang.String</method-param> </method-params> </query-method> <ejb-ql><![CDATA[ SELECT DISTINCT underling.organization.theBoss FROM gangster underling WHERE underling.name = ?1 OR underling.nickName = ?1 ]]></ejb-ql> </query> </entity> </enterprise-beans> </ejb-jar>
EJB-QL is similar to SQL but has some surprising differences. The following are some important things to note about EJB-QL:
EJB-QL is a typed language, meaning that it only allows comparison of like types (i.e., strings can only be compared with strings).
In an equals comparison a variable (single valued path) must be on the left hand side. Some examples follow:
g.hangout.state = 'CA' Legal 'CA' = g.shippingAddress.state NOT Legal 'CA' = 'CA' NOT Legal (r.amountPaid * .01) > 300 NOT Legal r.amountPaid > (300 / .01) Legal
Parameters use a base 1 index like java.sql.PreparedStatement.
Parameters are only allowed on the right hand side of a comparison. For example:
gangster.hangout.state = ?1 Legal ?1 = gangster.hangout.state NOT Legal