Criteria is a simplified API for retrieving entities by composing Criterion objects. This is a very convenient approach for functionality like "search" screens where there is a variable number of conditions to be placed upon the result set.

The Session is a factory for Criteria. Criterion instances are usually obtained via the factory methods on Restrictions. eg.

 List cats = session.createCriteria(Cat.class)
     .add( Restrictions.like("name", "Iz%") )
     .add( Restrictions.gt( "weight", new Float(minWeight) ) )
     .addOrder( Order.asc("age") )
     .list();
 

You may navigate associations using createAlias() or createCriteria().

 List cats = session.createCriteria(Cat.class)
     .createCriteria("kittens")
         .add( Restrictions.like("name", "Iz%") )
     .list();
 

 List cats = session.createCriteria(Cat.class)
     .createAlias("kittens", "kit")
     .add( Restrictions.like("kit.name", "Iz%") )
     .list();
 

You may specify projection and aggregation using Projection instances obtained via the factory methods on Projections.

 List cats = session.createCriteria(Cat.class)
     .setProjection( Projections.projectionList()
         .add( Projections.rowCount() )
         .add( Projections.avg("weight") )
         .add( Projections.max("weight") )
         .add( Projections.min("weight") )
         .add( Projections.groupProperty("color") )
     )
     .addOrder( Order.asc("color") )
     .list();