Chapter 12. Criteria Queries - Hibernate reference 2.1.8 ga 正式版英文参考手册

The interface net.sf.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 net.sf.hibernate.expression.Criterion. The class net.sf.hibernate.expression.Expression defines factory methods for obtaining certain built-in Criterion types.

List cats = sess.createCriteria(Cat.class)
    .add( Expression.like("name", "Fritz%") )
    .add( Expression.between("weight", minWeight, maxWeight) )
    .list();

Expressions may be grouped logically.

List cats = sess.createCriteria(Cat.class)
    .add( Expression.like("name", "Fritz%") )
    .add( Expression.or(
        Expression.eq( "age", new Integer(0) ),
        Expression.isNull("age")
    ) )
    .list();

List cats = sess.createCriteria(Cat.class)
    .add( Expression.in( "name", new String[] { "Fritz", "Izi", "Pk" } ) )
    .add( Expression.disjunction()
        .add( Expression.isNull("age") )
    	.add( Expression.eq("age", new Integer(0) ) )
    	.add( Expression.eq("age", new Integer(1) ) )
    	.add( Expression.eq("age", new Integer(2) ) )
    ) )
    .list();

There are quite a range of built-in criterion types (Expression subclasses), but one that is especially useful lets you specify SQL directly.

List cats = sess.createCriteria(Cat.class)
    .add( Expression.sql("lower({alias}.name) like lower(?)", "Fritz%", Hibernate.STRING) )
    .list();

The {alias} placeholder with be replaced by the row alias of the queried entity.

You may order the results using net.sf.hibernate.expression.Order.

List cats = sess.createCriteria(Cat.class)
    .add( Expression.like("name", "F%")
    .addOrder( Order.asc("name") )
    .addOrder( Order.desc("age") )
    .setMaxResults(50)
    .list();

You may easily specify constraints upon related entities by navigating associations using createCriteria().

List cats = sess.createCriteria(Cat.class)
    .add( Expression.like("name", "F%")
    .createCriteria("kittens")
        .add( Expression.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( Expression.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( Expression.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( Expression.like("name", "Fritz%") )
    .setFetchMode("mate", FetchMode.EAGER)
    .setFetchMode("kittens", FetchMode.EAGER)
    .list();

This query will fetch both mate and kittens by outer join.

The class net.sf.hibernate.expression.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();