Hibernate Criteria tutorial
The Hibernate Criteria API is a powerful library, which is well adapted for implementing multi-criteria search functionalities where queries must be built on the fly. For example it can be used to return data in a web search form resulting in cleaner, clearer, more reliable, and more maintainable code.
Here are some examples of the Criteria Api.
Basic Criteria (retrieve all data)
Criteria criteria = session.createCriteria(Track.class);
List<Track> tracks = criteria.list();
for (Track track : tracks) {
System.out.println("Title = " + track.getTitle());
System.out.println("Artist = " + track.getArtist().getName());
System.out.println("Genre = " + track.getGenre().getName());
}
List users = session.createCriteria(User.class)
.add( Restrictions.like("name", "Frank%") )
.add( Restrictions.between("age", minAge, maxAge) )
.list();
Criteria criteria = session.createCriteria(User.class)
.add(Restrictions.eq("id", new Long(1)));
User user = (User) criteria.uniqueResult();
List users = sess.createCriteria(User.class)
.add( Restrictions.sqlRestriction("lower({alias}.name) like lower(?)", "Frank%", Hibernate.STRING) )
.list();
Criteria criteria = session.createCriteria(User.class)
.addOrder(Order.asc("name"))
.setFirstResult(0)
.setMaxResults(10);
List<User> users = criteria.list();
for (User u : users) {
System.out.println("User = " + u.getName());
}
The class
org.hibernate.criterion.Projections is a factory for Projection instances. You can apply a projection to a query in order to retrieve some special criteria such as max/min/average value for a field or, most important, for counting the number of records in a query:
Criteria criteria = session.createCriteria(User.class)
.setProjection(Projections.max("age"));
Integer maxAge = (Integer) criteria.uniqueResult();
System.out.println("Max User age = " + maxAge);
criteria.setProjection(Projections.min("age"));
Integer minAge = (Integer) criteria.uniqueResult();
System.out.println("Min User age = " + minAge);
criteria.setProjection(Projections.avg("wage"));
Double avgWage = (Double) criteria.uniqueResult();
System.out.println("Avg User wage = " + avgWage);
criteria.setProjection(Projections.sum("wage"));
Integer totalWages = (Integer) criteria.uniqueResult();
System.out.println("Total Users wages = " + totalWages);
How to count the number of records in a query:
Criteria criteria = session.createCriteria(User.class)
.setProjection(Projections.rowCount());
List result = criteria.list();
if (!result.isEmpty()) {
Integer rowCount = (Integer) result.get(0);
System.out.println("Total Users: " + rowCount);
}
