Some EJB vendors provide object-to-relational mapping tools that, using wizards, can create object representations of relational databases, generate tables from objects, or map existing objects to existing tables. These tools are outside the scope of this book because they are proprietary in nature and cannot generally be used to produce beans that can be used across EJB servers. In other words, in many cases, once you have begun to rely on a mapping tool to define a bean’s persistence, you might not be able to migrate your beans to a different EJB server; the bean definition is bound to that mapping tool.
Mapping tools can make bean developers much more productive, but you should consider the implementation-specific details of your tool before using it. If you will need to migrate your application to a bigger, faster EJB server in the future, make sure the mapping tool you use is supported in other EJB servers.
Some products that perform object-to-relational mapping use JDBC. Object People’s TOPLink and Watershed’s ROF are examples of this type of product. These products provide more flexibility for mapping objects to relational databases and are not as dependent on the EJB server. However, EJB servers must support these products in order for them to be used, so again let caution guide your decisions about using these products.