setResultTransformer in Criteria

Question

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 clea

Answer 1

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)

Answer 2

Simply: when you are doing the Criteria: you want the resultset to be into particular object the you can use it like:eg:

 .setResultTransformer(Transformers.aliasToBean(Employee.class));

Employee should match the ResultSet Entity.