How to transform a flat result set using Hibernate

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Yes it is possible. You can use a custom transformer for it:
FluentHibernateResultTransformer.

You can copy paste code, or add the jar by Maven: fluent-hibernate-core.

You need to use Criteria with Projections. Please, don’t forget to specify projection aliases (userName, addressDetails.countryCode)

Criteria criteria = session.createCriteria(Customer.class);
criteria.createAlias("addressDetails", "addressDetails", JoinType.LEFT_OUTER_JOIN);

criteria.setProjection(Projections.projectionList()
        .add(Projections.property("userName").as("userName"))
        .add(Projections.property("addressDetails.countryCode")
        .as("addressDetails.countryCode")));

List<Customer> customers = criteria.setResultTransformer(
        new FluentHibernateResultTransformer(Customer.class)).list();

Using with HQL

It is impossible to use it with HQL, because of Hibernate doesn’t allow nested aliases in HQL

select addressDetails.countryCode as addressDetails.countryCode

It will be an error with the addressDetails.countryCode alias.

Using with a native SQL

The transformer can be used for a native SQL with the nested projections (opposite HQL).
It is need to use the aliases with the quotes in this case:

String sql = "select c.f_user_name as userName, d.f_country_code as \"addressDetails.countryCode\" "
        + "from customers c left outer join address_details d on c.fk_details = d.f_pid";

List<Customer> customers = session.createSQLQuery(sql)
        .setResultTransformer(new FluentHibernateResultTransformer(Customer.class))
        .list();

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