This approach is an alternative to the traditional J2EE object persistence solution—EJB 2.x entity beans—which has proven disappointing in practice for many reasons, including a cumbersome programming model, poor developer productivity, and poor testability.
Your persistence strategy not only can determine an application's performance, but can have a huge influence on the effort required to develop and maintain the application—and unless you make the right design decisions up front, it may be hard to revisit this part of the design after the application is finished.
Used appropriately, ORM can slash development effort, and improve maintainability. It is not unusual to see a saving of 30-50% in the amount of Java code that needs to be written by adopting an ORM solution, rather than JDBC.
If you're a TopLink user, you will appreciate the simplification and consistency that this can bring to your coding. Yet, you won't need to sacrifice any of the power of TopLink. If you've a Spring user, you have gained the choice of TopLink for your O-R mapping requirements
Read article Of Persistence and POJOs: Bridging the Object & Relational World
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