How to Convert Native Query Results to POJO Collections in JPA?

Converting Native Query Results to POJO Collections in JPA

Using JPA, it is possible to execute native SQL queries and retrieve the results. However, by default, these results are returned as arrays of objects. If you wish to convert them into collections of Plain Old Java Objects (POJO) with specific fields, there are several approaches available.

Using Mapped Entities (JPA 2.0)

In JPA 2.0, native queries can be mapped to JPA entities. This means that the POJO class used to represent the result must be a mapped entity, meaning it has been annotated with appropriate JPA annotations. The resultClass attribute of the NamedNativeQuery annotation can be used to specify this class.

Manual Mapping

Prior to JPA 2.1, a manual mapping approach was used. This involved writing code to map the tuple array returned by the native query to the POJO class. This mapping could be accomplished using reflection.

Using @SqlResultSetMapping (JPA 2.1)

With the introduction of JPA 2.1, the @SqlResultSetMapping annotation allows explicit mapping of native query results to POJO classes. This approach does not require the POJO to be a JPA entity.

Using XML Mapping

In cases where declaring named queries within entities is undesirable, an alternative XML mapping approach can be used. The sql-result-set-mapping element can be defined in the META-INF/orm.xml file to map the native query results to a specific POJO class.

Conclusion

Depending on your version of JPA and the specific requirements of your project, there are several methods available for converting native query results to POJO collections. The choice of approach will depend on factors such as JPA compatibility, the nature of the POJO class, and the desired level of configuration.

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