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

问题

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();

回答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"))
        );

回答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();

回答3:

or setProjection(Projections.id())

回答4:

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

回答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();

回答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();

回答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

来源：https://stackoverflow.com/questions/58561/how-to-use-hibernate-criteria-to-return-only-one-element-of-an-object-instead-th

标签

hibernate

criteria