小结Hibernate的查询办法[Java编程]

1. get() and load()

session.get(Clazz, id);
session.load(Clazz, id);

阐明: load()与get()的辨别

请注意假如没有匹配的数据库记录,load()办法大概抛出无法恢复的非常(unrecoverable exception). 假如类的映射利用了代理(proxy),load()办法会返回一个未初始化的代理,直到你调用该代理的某办法时才会去拜候数据库. 若你但愿在某对象中成立一个指向另一个对象的关联,又不想在从数据库中装载该对象时同时装载相关联的那个对象,那么这种操作方法就用得上的了. 假如为呼应类映射关系设置了batch-size, 那么利用这种操作方法允很多个对象被一批装载(因为返回的是代理,无需从数据库中抓取全部对象的数据).

假如你不肯定能否有匹配的行存在,应当利用get()办法,它会立即拜候数据库,假如没有对应的行,会返回null.

2. HQL

// 返回一行记录
String hql = "from TOrder o where o.id = ?";
TOrder o = (TOrder) s.createQuery(hql)
.setParameter(0, orderId)
.uniqueResult();
// 命名参数
Query q = sess.createQuery("from DomesticCat cat where cat.name = :name");
q.setString("name", "Fritz");
// 位置参数
Query q = sess.createQuery("from DomesticCat cat where cat.name = ?");
q.setString(0, "Izi");
// 命名参数列表
Query q = sess.createQuery("from DomesticCat cat where cat.name in (:namesList)");
q.setParameterList("namesList", names);
// 分页查询
Query q = sess.createQuery("from DomesticCat cat");
q.setFirstResult(20);
q.setMaxResults(10);
List cats = q.list();

3. Criteria

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

4. Native SQL

String treeSql = "" +
"select , level from tree t " +
" start with t.parent_id = 0 " +
" connect by prior t.id = t.parent_id";
List result = session.createSQLQuery(treeSql)
.addEntity("t", Tree.class)
.addScalar("level", Hibernate.INTEGER)
.list();

5. Named SQL queries(不举荐)

6. filter(不举荐)

7. Detached queries(还没测试)

The DetachedCriteria class lets you create a query outside the scope of a session, and then later execute it using some arbitrary Session