setResultTransformer in Criteria

hibernate criteria hibernate-criteria
user182944 picture user182944 · Jun 9, 2012 · Viewed 48.4k times · Source

What is the use of setResultTransformer method in criteria API? Can someone explain this with a simple example? I read the javadocs but i am not able to understand them clearly.

Regards,

Answer

carbontax picture carbontax · Jun 9, 2012

The default ResultTransformer for a Criteria query which does not use setProjections() will be ROOT_ENTITY.

If we have Student in a ManyToMany relationship to Department a query might look like this ...

    Session session = (Session) getEntityManager().getDelegate();
    Criteria crit = session.createCriteria(Student.class)
        .createAlias('departments', 'department');

This query will return duplicates. But set the ResultTransformer as ...

    crit.setResultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY);

Now the results will be distinct when Hibernate marshalls the results. (Or do I mean unmarshalls?)

If you do not want Hibernate to return the query as a List<Student> but prefer to handle the results as a List<Object[]> then 

    crit.setResultTransformer(CriteriaSpecification.PROJECTION)

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