web server - Borland Technical Publications

Chapter
17
17EJB-QL and Data Access Support
Chapter
Important
EJB-QL allows you to specify queries in an object oriented query language, EJB-QL.
The Borland CMP engine translates these queries into SQL queries. The Borland
Enterprise Server provides some extensions to the EJB-QL functionality described in
the Sun Microsystems EJB 2.x Specification.
For documentation updates, go to www.borland.com/techpubs/bes.
Selecting a CMP Field or Collection of CMP Fields
When only one cmp-field of an otherwise large EJB is required, you can use EJB-QL to
select a single instance of collection of that cmp-field. Using EJB-QL in this way
improves application performance by eliminating the need to load an entire EJB. For
example, this query method selects only the balance field from the Account table:
ejbSelectBalanceOfAccountLineItem
java.lang.Long
Local
SELECT l.balance FROM Account a, IN (a.accountLineItem) l WHERE
l.lineItemId=?1
The return types of the EJB-QL query method are:
■
■
■
■
If the Java type of the cmp-field is an object type, and the query method is a singleobject
query method, the return type is an instance of that object type.
If the Java type of the cmp-field is an object type and the query method returns
multiple objects, a collection of instances of the object type is returned.
If the Java type of the cmp-field is a primitive Java type, and the SELECT method is
a single-object method, the return type is that primitive type.
If the Java type of the cmp-field is a primitive Java type, and the SELECT method is
for multiple objects, a collection of the wrappered Java type is returned.
Chapter 17: EJB-QL and Data Access Support 153