How to return an entity with chosen columns using Criteria

Question

I'm really new with Hibernate. I want a List<User> using hibernate criteria, but only with fields User id and name filled up. Is that possible? Something like the query shown below:

SELECT user.id, user.name FROM user

Regards.

Answer 1

Typically you don't want to partially load the properties of an object. But if you must see this:

http://docs.jboss.org/hibernate/stable/core/reference/en/html/performance.html#performance-fetching-lazyproperties

For plain reporting-like behaviour you could use entity queries:

sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE FROM CATS").addEntity(Cat.class);

http://docs.jboss.org/hibernate/stable/core/reference/en/html/querysql.html#d0e13573

Answer 2

Hi Rodrigo. This is exactly what projections are for. Here is an example:

  Criteria cr = session.createCriteria(User.class)
    .setProjection(Projections.projectionList()
      .add(Projections.property("id"), "id")
      .add(Projections.property("Name"), "Name"))
    .setResultTransformer(Transformers.aliasToBean(User.class));

  List<User> list = cr.list();

In fact, if you look at the documentation for "lazy property fetching" they specifically say:

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"A different (better?) way to avoid unnecessary column reads, at least for read-only transactions is to use the projection features of HQL or Criteria queries. This avoids the need for buildtime bytecode processing and is certainly a preferred solution."

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By the way, there is a related question that you may also be interested in: http://stackoverflow.com/questions/84644/hibernate-query-by-example-and-projections