Hibernate features an intuitive, extensible criteria query API.
The interface org.hibernate.Criteria represents a query against a particular persistent class. The Session is a factory for Criteria instances.
Criteria crit = sess.createCriteria(Cat.class); crit.setMaxResults(50); List cats = crit.list();
An individual query criterion is an instance of the interface org.hibernate.criterion.Criterion. The class org.hibernate.criterion.Restrictions defines factory methods for obtaining certain built-in Criterion types.
List cats = sess.createCriteria(Cat.class) .add( Restrictions.like("name", "Fritz%") ) .add( Restrictions.between("weight", minWeight, maxWeight) ) .list();
Restrictions may be grouped logically.
List cats = sess.createCriteria(Cat.class) .add( Restrictions.like("name", "Fritz%") ) .add( Restrictions.or( Restrictions.eq( "age", new Integer(0) ), Restrictions.isNull("age") ) ) .list();
List cats = sess.createCriteria(Cat.class) .add( Restrictions.in( "name", new String[] { "Fritz", "Izi", "Pk" } ) ) .add( Restrictions.disjunction() .add( Restrictions.isNull("age") ) .add( Restrictions.eq("age", new Integer(0) ) ) .add( Restrictions.eq("age", new Integer(1) ) ) .add( Restrictions.eq("age", new Integer(2) ) ) ) ) .list();
There are quite a range of built-in criterion types (Restrictions subclasses), but one that is especially useful lets you specify SQL directly.
List cats = sess.createCriteria(Cat.class) .add( Restrictions.sql("lower({alias}.name) like lower(?)", "Fritz%", Hibernate.STRING) ) .list();
The {alias} placeholder with be replaced by the row alias of the queried entity.
An alternative approach to obtaining a criterion is to get it from a Property instance. You can create a Property by calling Property.forName().
Property age = Property.forName("age"); List cats = sess.createCriteria(Cat.class) .add( Restrictions.disjunction() .add( age.isNull() ) .add( age.eq( new Integer(0) ) ) .add( age.eq( new Integer(1) ) ) .add( age.eq( new Integer(2) ) ) ) ) .add( Property.forName("name").in( new String[] { "Fritz", "Izi", "Pk" } ) ) .list();
You may order the results using org.hibernate.criterion.Order.
List cats = sess.createCriteria(Cat.class) .add( Restrictions.like("name", "F%") .addOrder( Order.asc("name") ) .addOrder( Order.desc("age") ) .setMaxResults(50) .list();
List cats = sess.createCriteria(Cat.class) .add( Property.forName("name").like("F%") ) .addOrder( Property.forName("name").asc() ) .addOrder( Property.forName("age").desc() ) .setMaxResults(50) .list();
You may easily specify constraints upon related entities by navigating associations using createCriteria().
List cats = sess.createCriteria(Cat.class) .add( Restrictions.like("name", "F%") .createCriteria("kittens") .add( Restrictions.like("name", "F%") .list();
note that the second createCriteria() returns a new instance of Criteria, which refers to the elements of the kittens collection.
The following, alternate form is useful in certain circumstances.
List cats = sess.createCriteria(Cat.class) .createAlias("kittens", "kt") .createAlias("mate", "mt") .add( Restrictions.eqProperty("kt.name", "mt.name") ) .list();
(createAlias() does not create a new instance of Criteria.)
Note that the kittens collections held by the Cat instances returned by the previous two queries are not pre-filtered by the criteria! If you wish to retrieve just the kittens that match the criteria, you must use returnMaps().
List cats = sess.createCriteria(Cat.class) .createCriteria("kittens", "kt") .add( Restrictions.eq("name", "F%") ) .returnMaps() .list(); Iterator iter = cats.iterator(); while ( iter.hasNext() ) { Map map = (Map) iter.next(); Cat cat = (Cat) map.get(Criteria.ROOT_ALIAS); Cat kitten = (Cat) map.get("kt"); }
You may specify association fetching semantics at runtime using setFetchMode().
List cats = sess.createCriteria(Cat.class) .add( Restrictions.like("name", "Fritz%") ) .setFetchMode("mate", FetchMode.EAGER) .setFetchMode("kittens", FetchMode.EAGER) .list();
This query will fetch both mate and kittens by outer join. See Section 20.1, “Fetching strategies” for more information.
The class org.hibernate.criterion.Example allows you to construct a query criterion from a given instance.
Cat cat = new Cat(); cat.setSex('F'); cat.setColor(Color.BLACK); List results = session.createCriteria(Cat.class) .add( Example.create(cat) ) .list();
Version properties, identifiers and associations are ignored. By default, null valued properties are excluded.
You can adjust how the Example is applied.
Example example = Example.create(cat) .excludeZeroes() //exclude zero valued properties .excludeProperty("color") //exclude the property named "color" .ignoreCase() //perform case insensitive string comparisons .enableLike(); //use like for string comparisons List results = session.createCriteria(Cat.class) .add(example) .list();
You can even use examples to place criteria upon associated objects.
List results = session.createCriteria(Cat.class) .add( Example.create(cat) ) .createCriteria("mate") .add( Example.create( cat.getMate() ) ) .list();
The class org.hibernate.criterion.Projections is a factory for Projection instances. We apply a projection to a query by calling setProjection().
List results = session.createCriteria(Cat.class) .setProjection( Projections.rowCount() ) .add( Restrictions.eq("color", Color.BLACK) ) .list();
List results = session.createCriteria(Cat.class) .setProjection( Projections.projectionList() .add( Projections.rowCount() ) .add( Projections.avg("weight") ) .add( Projections.max("weight") ) .add( Projections.groupProperty("color") ) ) .list();
There is no explicit "group by" necessary in a criteria query. Certain projection types are defined to be grouping projections, which also appear in the SQL group by clause.
An alias may optionally be assigned to a projection, so that the projected value may be referred to in restrictions or orderings. Here are two different ways to do this:
List results = session.createCriteria(Cat.class) .setProjection( Projections.alias( Projections.groupProperty("color"), "colr" ) ) .addOrder( Order.asc("colr") ) .list();
List results = session.createCriteria(Cat.class) .setProjection( Projections.groupProperty("color").as("colr") ) .addOrder( Order.asc("colr") ) .list();
The alias() and as() methods simply wrap a projection instance in another, aliased, instance of Projection. As a shortcut, you can assign an alias when you add the projection to a projection list:
List results = session.createCriteria(Cat.class) .setProjection( Projections.projectionList() .add( Projections.rowCount(), "catCountByColor" ) .add( Projections.avg("weight"), "avgWeight" ) .add( Projections.max("weight"), "maxWeight" ) .add( Projections.groupProperty("color"), "color" ) ) .addOrder( Order.desc("catCountByColor") ) .addOrder( Order.desc("avgWeight") ) .list();
List results = session.createCriteria(Domestic.class, "cat") .createAlias("kittens", "kit") .setProjection( Projections.projectionList() .add( Projections.property("cat.name"), "catName" ) .add( Projections.property("kit.name"), "kitName" ) ) .addOrder( Order.asc("catName") ) .addOrder( Order.asc("kitName") ) .list();
You can also use Property.forName() to express projections:
List results = session.createCriteria(Cat.class) .setProjection( Property.forName("name") ) .add( Property.forName("color").eq(Color.BLACK) ) .list();
List results = session.createCriteria(Cat.class) .setProjection( Projections.projectionList() .add( Projections.rowCount().as("catCountByColor") ) .add( Property.forName("weight").avg().as("avgWeight") ) .add( Property.forName("weight").max().as("maxWeight") ) .add( Property.forName("color").group().as("color" ) ) .addOrder( Order.desc("catCountByColor") ) .addOrder( Order.desc("avgWeight") ) .list();
The DetachedCriteria class lets you create a query outside the scope of a session, and then later execute it using some arbitrary Session.
DetachedCriteria query = DetachedCriteria.forClass(Cat.class) .add( Property.forName("sex").eq('F') ); Session session = ....; Transaction txn = session.beginTransaction(); List results = query.getExecutableCriteria(session).setMaxResults(100).list(); txn.commit(); session.close();
A DetachedCriteria may also be used to express a subquery. Criterion instances involving subqueries may be obtained via Subqueries or Property.
DetachedCriteria avgWeight = DetachedCriteria.forClass(Cat.class) .setProjection( Property.forName("weight").avg() ); session.createCriteria(Cat.class) .add( Property.forName("weight).gt(avgWeight) ) .list();
DetachedCriteria weights = DetachedCriteria.forClass(Cat.class) .setProjection( Property.forName("weight") ); session.createCriteria(Cat.class) .add( Subqueries.geAll("weight", weights) ) .list();
Even correlated subqueries are possible:
DetachedCriteria avgWeightForSex = DetachedCriteria.forClass(Cat.class, "cat2") .setProjection( Property.forName("weight").avg() ) .add( Property.forName("cat2.sex").eqProperty("cat.sex") ); session.createCriteria(Cat.class, "cat") .add( Property.forName("weight).gt(avgWeightForSex) ) .list();