How to use hibernate criteria to return only one element of an object instead the entire object?

Question

I'm trying to get only the list of id of object bob for example instead of the list of bob. It's ok with a HQL request, but I would know if it's possible using criteria ?

An example :

final StringBuilder hql = new StringBuilder();
hql.append( "select bob.id from " )
    .append( bob.class.getName() ).append( " bob " )
    .append( "where bob.id > 10");

final Query query = session.createQuery( hql.toString() );
return query.list();

Answer 1

I think you could do that with Projections, something like

Criteria.forClass(bob.class.getName())
        .add(Restrictions.gt("id", 10))
        .setProjection(Projections.property("id"))
        );

Answer 2

Similarly you can also:

Criteria criteria = session.createCriteria(bob.class);

criteria.add(Expression.gt("id", 10));

criteria.setProjection(Projections.property("id"));

criteria.addOrder(Order.asc("id"));

return criteria.list();

Answer 3

or setProjection(Projections.id())

Answer 4

http://www.devarticles.com/c/a/Java/Hibernate-Criteria-Queries-in-Depth/2/

Answer 5

SessionFactory sessionFactory;    
Criteria crit=sessionFactory.getCurrentSession().createCriteria(Model.class);
crit.setProjection(Projections.property("id"));
List result = crit.list();

This code code will give you list of ids in the model class like [1,2,3]. if you wants to get the array list like [{"id":1},{"id":2}] then use the following code

SessionFactory sessionFactory;    
Criteria crit=sessionFactory.getCurrentSession().createCriteria(Model.class); 
crit.setProjection(Projections.property("id").as("id")); 
List result = crit.setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP).list();

Answer 6

Another option (though a bit un hibernate-esque) is to use "raw" sql, like this:

List<Long> myList = session.createSQLQuery("select single_column from table_name")
          .addScalar("single_column", StandardBasicTypes.LONG).list();

Answer 7

You can do that like this

    bob bb=null;

    Criteria criteria = session.createCriteria(bob.class);  
    criteria.add(Restrictions.eq("id",id));

    bb = (bob) criteria.uniqueResult();

as Restrictions you can add your condition