getting result set into DTO in SQL Query in Hibernate

Question

I have a query like below

select f.id, s.name, ss.name
from first f
left join second s on f.id = s.id
left join second ss on f.sId = ss.id

If I could have used HQL, I would have used constructor syntax to directly populate DTO with the result set. But, since hibernate don't allow left join without having an association in place I have to use the Native Query.

Currently I am looping through the result set in JDBC style and populating DTO objects. Is there any simpler way to achieve it?

Answer 1

You could maybe use a result transformer. Quoting Hibernate 3.2: Transformers for HQL and SQL:

SQL Transformers

With native sql returning non-entity beans or Map's is often more useful instead of basic Object[]. With result transformers that is now possible.

List resultWithAliasedBean = s.createSQLQuery(
  "SELECT st.name as studentName, co.description as courseDescription " +
  "FROM Enrolment e " +
  "INNER JOIN Student st on e.studentId=st.studentId " +
  "INNER JOIN Course co on e.courseCode=co.courseCode")
  .addScalar("studentName")
  .addScalar("courseDescription")
  .setResultTransformer( Transformers.aliasToBean(StudentDTO.class))
  .list();

StudentDTO dto =(StudentDTO) resultWithAliasedBean.get(0);

Tip: the addScalar() calls were required on HSQLDB to make it match a property name since it returns column names in all uppercase (e.g. "STUDENTNAME"). This could also be solved with a custom transformer that search the property names instead of using exact match - maybe we should provide a fuzzyAliasToBean() method ;)

References

• Hibernate Reference Guide
  • 16.1.5. Returning non-managed entities
• Hibernate's Blog
  • Hibernate 3.2: Transformers for HQL and SQL