Yet again, this job falls to the deployment descriptor.
Associating an EJB QL statement with a method begins with specifying the query element. You specify the query element as the very last child of the entity element — after the CMP fields, primary key, and any environment information:
<entity>
...
<cmp−field> .... </cmp−field>
<primkey−field>orderID</primkey−field>
...
<query> ??? </query>
</entity>
The query element contains a fair bit of information — aimed primarily at correctly identifying the method with which you are associating the statement. The element can be broken down into two main parts and one optional part.
Apart from the EJB QL text of the query, you need to define the method that should use the query statement.
Because the descriptor is XML, describing a method can be quite tedious and verbose. Each method is described by a name and set of arguments in the deployment descriptor. As you are aware, methods can be overloaded, so a name alone is not sufficient — some of the time. If you don't have an overloaded method name that you are lining up with a query, then you can take some shortcuts.
Method declarations are handled by the query−method element. The first child element is the name of the method, enclosed in the method−name element. After the method name come the parameters (if any) collected together in the method−params element.
<query>
<query−method>ejbFindByCategory</query−method>
<method−params> ??? </method−params>
</query>
Tip
The method name provided must be the name in the bean−implementation class, not the home interface. In other words, every name you use here should start with ejbFind or ejbSelect.
In this example, only one method in the product home interface has the name findByCategory. That means you can leave the method−params element empty. You can't remove it entirely, because it is required, but an empty declaration is allowed.
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Chapter 17: Using Advanced EJB Techniques
A single method parameter is declared using the single method−param element (note the lack of an s). The parameter declares the datatype (class or primitive) rather than the name. So if your method takes a string, then you would use the following declaration:
<method−param>java.lang.String</method−param>
The full declaration is as follows:
<method−params>
<method−param>java.lang.String</method−param>
</method−params>
For more than one parameter, you must declare the types in the order in which they are declared in the Java class. Examining the LocalProductHome local home interface, you can see that the findByCategory method takes two strings as the parameters. The deployment descriptor representation of the method is as follows:
<query>
<query−method>ejbFindByCategory</query−method>
<method−params>
<method−param>java.lang.String</method−param>
<method−param>java.lang.String</method−param>
</method−params>
</query>
Now you need to tidy up by adding the EJB QL statement using the ejb−ql element. This final element is declared after the method−params element. To include the EJB QL statement, just wrap it in the opening and closing tag like this:
<ejb−ql>SELECT ENTITY(p) FROM Product p
WHERE p.category = ?1 AND p.name LIKE %?2% </ejb−ql>
Tip If you have a statement that uses the greater−than or less−than characters (< or >), you cannot use these characters directly. Remember that the text here is XML, which means these are reserved characters that must be encoded using > and < in accordance with the rules of XML.
You have now completed all the work that is needed to describe queries for a container−managed entity bean.