Hibernate的查询方式
Hibernate的查询方式有：
1.使用主键id加载对象(load(),get());
2.通过对象导航,比如通过stu.getTeam()得到team的实例;
3.使用hql;
4.使用qbc(query by criteria)
5.直接使用sql语句取得记录集;
一般都使用后面三种方式.
注意.hql是面向对象的查询.语法和sql是基本一样的.不区分大小写的,但是注意的是对与对象.必须遵循对象的大小写.因为hql是对像查询..同时我们必须清楚.hql只能取得对象,而不支持uid(update,insert.delete)
HQL功能最强大，适合各种情况，但是动态条件查询构造起来很不方便
Criteria最适合动态条件查询，不太适合统计查询，QBE还不够强大，只适合相当简单的查询
NativeSQL可以实现特定数据库的SQL，但是可移植性就牺牲了
Hibernate2的Criteria功能不够完善，所以Hibernate2上面可用的只有HQL和NativeSQL，Hibernate3的Criteria已经非常强大了。
针对web应用来说，大部分常规查询都是动态条件查询，所以首选使用Criteria，并且Hibernate3提供了DetachedCriteria，可以在web层构造好DetachedCriteria再进入session执行查询，非常方便实用的特性。
但是涉及到统计查询和非常复杂的关联查询，Criteria就无能为力了，这种情况下我选择使用HQL。
以下是HQL/QBC/Native SQL三种查询策略
HQL策略：
Java代码
session.createQuery("FROM Category c where c.name like 'Laptop%'");
session.createQuery("FROM Category c where c.name like 'Laptop%'");
QBC策略：
Java代码
session.createCriteria(Category.class).add(Restrictions.like("name", "Laptop%"));
session.createCriteria(Category.class).add(Restrictions.like("name", "Laptop%"));
Native SQL策略
Java代码
session.createSQLQuery("select {c.*} from CATEGORY {c} where NAME like 'Laptop%'").
addEntity("c",Category.class);
session.createSQLQuery("select {c.*} from CATEGORY {c} where NAME like 'Laptop%'").
addEntity("c",Category.class);
节 8.02 分页查询
Java代码
Criteria criteria = session.createCriteria(Category.class)
.add(Restrictions.like("name", "Laptop%"));
criteria.addOrder(Order.asc("name"));
criteria.setFirstResult(0);//初始行数
criteria.setMaxResults(20);//每页显示行数
Criteria criteria = session.createCriteria(Category.class)
.add(Restrictions.like("name", "Laptop%"));
criteria.addOrder(Order.asc("name"));
criteria.setFirstResult(0);//初始行数
criteria.setMaxResults(20);//每页显示行数
节 8.03 数据过滤
方法 说明
Restrictions.eq =
Restrictions.allEq 利用Map来进行多个等于的限制
Restrictions.gt >
Restrictions.ge >=
Restrictions.lt <
Restrictions.le <=
Restrictions.between BETWEEN
Restrictions.like LIKE
Restrictions.in in
Restrictions.and and
Restrictions.or or
Restrictions.sqlRestriction 用SQL限定查询
(a) 应用限制
Java代码
Criterion emailEq = Restrictions.eq("email", "[email protected]");
Criteria criteria = session.createCriteria(User.class);
criteria.add(emailEq);
User user = (User)criteria.uniqueResult();
Criterion emailEq = Restrictions.eq("email", "[email protected]");
Criteria criteria = session.createCriteria(User.class);
criteria.add(emailEq);
User user = (User)criteria.uniqueResult();
(b) 比较表达式
Java代码
Restrictions.between("amount", new BigDecimal(100), new BigDecimal(200));
Restrictions.gt("amount", new BigDecimal(100));
Restrictions.in("email", emails);//注：emails为集合
Restrictions.isNull("email");
Restrictions.isNotNull("email");
Restrictions.isEmpty("bids");
Restrictions.sizeGe("bids", 3);//bids属性大小
Restrictions.between("amount", new BigDecimal(100), new BigDecimal(200));
Restrictions.gt("amount", new BigDecimal(100));
Restrictions.in("email", emails);//注：emails为集合
Restrictions.isNull("email");
Restrictions.isNotNull("email");
Restrictions.isEmpty("bids");
Restrictions.sizeGe("bids", 3);//bids属性大小
(c) 字符串匹配
Java代码
Restrictions.like("email", "G%");
Restrictions.like("email", "G%",MatchMode.START);
注：MatchMode分为START,END,ANYWHERE,EXACT四种模式
Restrictions.like("email", "G%").ignoreCase();
Restrictions.like("email", "G%");
Restrictions.like("email", "G%",MatchMode.START);
注：MatchMode分为START,END,ANYWHERE,EXACT四种模式
Restrictions.like("email", "G%").ignoreCase();
(d) 组合表达式和逻辑操作符
Java代码
Restrictions.or(
Restrictions.and(
Restrictions.like("firstname", "G%"),
Restrictions.like("lastname", "K%")),
Restrictions.in("email",emails));
Restrictions.or(
Restrictions.and(
Restrictions.like("firstname", "G%"),
Restrictions.like("lastname", "K%")),
Restrictions.in("email",emails));
(e) SQL表达式
Java代码
Restrictions.sqlRestriction("{alias}.name='tie' and {alias}.addr='dalian'");
Restrictions.sqlRestriction("{alias}.name=?", "tie", Hibernate.STRING);//姓名为tie的对象
Restrictions.sqlRestriction("length({alias}.PASSWORD) < ?",5,Hibernate.INTEGER);
//密码小于5个字符对象
Restrictions.sqlRestriction("'100' >all( select b.AMOUNT FROM BID b " +
" WHERE b.ITEM_ID = {alias}.ITEM_ID)");//返回出价不大于100
Restrictions.sqlRestriction("{alias}.name='tie' and {alias}.addr='dalian'");
Restrictions.sqlRestriction("{alias}.name=?", "tie", Hibernate.STRING);//姓名为tie的对象
Restrictions.sqlRestriction("length({alias}.PASSWORD) < ?",5,Hibernate.INTEGER);
//密码小于5个字符对象
Restrictions.sqlRestriction("'100' >all( select b.AMOUNT FROM BID b " +
" WHERE b.ITEM_ID = {alias}.ITEM_ID)");//返回出价不大于100
(f) 子查询
节 8.04 表关联
(a) 隐式关联
隐式关联有两种方法：
1、 Criteria接口的createCriteria()方法：
Java代码
session.createCriteria(Item.class)
.add(Restrictions.like("description", "Foo",MatchMode.ANYWHERE))
.createCriteria("bids")
.add(Restrictions.gt("amount",new BigDecimal(100)));
session.createCriteria(Item.class)
.createCriteria("seller")
.add(Restrictions.like("email", "%@"));
session.createCriteria(Item.class)
.add(Restrictions.like("description", "Foo",MatchMode.ANYWHERE))
.createCriteria("bids")
.add(Restrictions.gt("amount",new BigDecimal(100)));
session.createCriteria(Item.class)
.createCriteria("seller")
.add(Restrictions.like("email", "%@"));
2、 分配别名：
Java代码
session.createCriteria(Item.class)
.createAlias("bids","b")
.add(Restrictions.like("description", "%Foo%"))
.add(Restrictions.gt("b.amount", new BigDecimal(100)));
session.createCriteria(Item.class)
.createAlias("seller", "s")
.add(Restrictions.like("s.email","%@"));
session.createCriteria(Item.class)
.createAlias("bids","b")
.add(Restrictions.like("description", "%Foo%"))
.add(Restrictions.gt("b.amount", new BigDecimal(100)));
session.createCriteria(Item.class)
.createAlias("seller", "s")
.add(Restrictions.like("s.email","%@"));
(b) 抓取关联
Java代码
session.createCriteria(Item.class)
.setFetchMode("bids",FetchMode.JOIN)
.add(Restrictions.like("description", "%Foo%"))
session.createCriteria(Item.class)
.setFetchMode("bids",FetchMode.JOIN)
.add(Restrictions.like("description", "%Foo%"))
节 8.05 投影/报表查询
(a) 简单投影
Java代码
session.createCriteria(Item.class)
.add(Restrictions.gt("endDate", new Date()))
.setProjection(Projections.id());//返回单一属性
session.createCriteria(Item.class).setProjection(
Projections.projectionList().add(Projections.id()).
add(Projections.property("description")));//返回一个Object[]
session.createCriteria(Item.class)
.add(Restrictions.gt("endDate", new Date()))
.setProjection(Projections.id());//返回单一属性
session.createCriteria(Item.class).setProjection(
Projections.projectionList().add(Projections.id()).
add(Projections.property("description")));//返回一个Object[]
(b) 统计分组
Java代码
session.createCriteria(Item.class)
.setProjection(Projections.rowCount());
session.createCriteria(Item.class)
.setProjection(Projections.projectionList()
.add(Projections.rowCount())
.add(Projections.sum("sales"))
.add(Projections.avg("score"))
);
session.createCriteria(Bid.class)
.createAlias("bidder", "u")
.setProjection(Projections.projectionList()
.add(Property.forName("u.id").group())
.add(Property.forName("u.username").group())
.add(Property.forName("id").count())
.add(Property.forName("amount").avg())
);
session.createCriteria(Item.class)
.setProjection(Projections.rowCount());
session.createCriteria(Item.class)
.setProjection(Projections.projectionList()
.add(Projections.rowCount())
.add(Projections.sum("sales"))
.add(Projections.avg("score"))
);
session.createCriteria(Bid.class)
.createAlias("bidder", "u")
.setProjection(Projections.projectionList()
.add(Property.forName("u.id").group())
.add(Property.forName("u.username").group())
.add(Property.forName("id").count())
.add(Property.forName("amount").avg())
);
(c) SQL投影
Java代码
String sqlFragment = "(select count(*) from Item i where i.item_id = item_id) "
+ " as numofitems";
session.createCriteria(Bid.class).createAlias("bidder", "u")
.setProjection(
Projections.projectionList().add(
Projections.groupProperty("u.id")).add(
Projections.groupProperty("u.username")).add(
Projections.count("id")).add(
Projections.avg("amount")).add(
Projections.sqlProjection(sqlFragment,
new String[] { "numofitems" },
new Type[] { Hibernate.LONG }))
);