Hibernate-Lesson4

查询总结

1.oid查询-get

2.对象属性导航查询

3.HQL

4.Criteria

5.原生SQL

查询-HQL语法

基础语法

String hql = " from  cn.itheima.domain.Customer ";//完整写法
String hql2 = " from  Customer "; //简单写法
String hql3 = " from java.lang.Object "; 

Query query = session.createQuery(hql3);

List list = query.list();

System.out.println(list);

排序

String hql1 = " from  cn.itheima.domain.Customer order by cust_id asc ";//完整写法
String hql2 = " from  cn.itheima.domain.Customer order by cust_id desc ";//完整写法

Query query = session.createQuery(hql2);

List list = query.list();

System.out.println(list);

条件

String hql1 = " from  cn.itheima.domain.Customer where cust_id =? ";//完整写法
String hql2 = " from  cn.itheima.domain.Customer where cust_id = :id ";//完整写法

Query query = session.createQuery(hql2);

//        query.setParameter(0, 2l);
query.setParameter("id", 2l);


List list = query.list();

System.out.println(list);

分页

String hql1 = " from  cn.itheima.domain.Customer  ";//完整写法

Query query = session.createQuery(hql1);

//limit ?,?
// (当前页数-1)*每页条数
query.setFirstResult(2);
query.setMaxResults(2);

List list = query.list();

System.out.println(list);

聚合

String hql1 = " select count(*) from  cn.itheima.domain.Customer  ";//完整写法
String hql2 = " select sum(cust_id) from  cn.itheima.domain.Customer  ";//完整写法
String hql3 = " select avg(cust_id) from  cn.itheima.domain.Customer  ";//完整写法
String hql4 = " select max(cust_id) from  cn.itheima.domain.Customer  ";//完整写法
String hql5 = " select min(cust_id) from  cn.itheima.domain.Customer  ";//完整写法

Query query = session.createQuery(hql5);

Number number  = (Number) query.uniqueResult();

System.out.println(number);

投影

String hql1 = " select cust_name from  cn.itheima.domain.Customer  ";
String hql2 = " select cust_name,cust_id from  cn.itheima.domain.Customer  ";
String hql3 = " select new Customer(cust_id,cust_name) from  cn.itheima.domain.Customer  ";

Query query = session.createQuery(hql3);

List list = query.list();

System.out.println(list);

多表查询

SQL

	//回顾-原生SQL
	// 交叉连接-笛卡尔积(避免)
//		select * from A,B 
	// 内连接
//		|-隐式内连接
//			select * from A,B  where b.aid = a.id
//		|-显式内连接
//			select * from A inner join B on b.aid = a.id
	// 外连接
//		|- 左外
//			select * from A left [outer] join B on b.aid = a.id
//		|- 右外
//			select * from A right [outer] join B on b.aid = a.id

HQL

//HQL的多表查询
		//内连接(迫切)
		//外连接
//			|-左外(迫切)
//			|-右外(迫切)

HQL语法

内连接

String hql = " from Customer c inner join c.linkMens ";

Query query = session.createQuery(hql);

List<Object[]> list = query.list();

for(Object[] arr : list){
    System.out.println(Arrays.toString(arr));
}

String hql = " from Customer c inner join fetch c.linkMens ";

Query query = session.createQuery(hql);

List<Customer> list = query.list();

System.out.println(list);

左外链接

String hql = " from Customer c left join c.linkMens ";

Query query = session.createQuery(hql);

List<Object[]> list = query.list();

for(Object[] arr : list){
    System.out.println(Arrays.toString(arr));
}

右外连接

String hql = " from Customer c right join c.linkMens ";

Query query = session.createQuery(hql);

List<Object[]> list = query.list();

for(Object[] arr : list){
    System.out.println(Arrays.toString(arr));
}

查询-Criteria语法

语法

基本

Criteria c = session.createCriteria(Customer.class);

List<Customer> list = c.list();

System.out.println(list);

条件

Criteria c = session.createCriteria(Customer.class);

//        c.add(Restrictions.idEq(2l));
c.add(Restrictions.eq("cust_id",2l));

List<Customer> list = c.list();

System.out.println(list);

分页

Criteria c = session.createCriteria(Customer.class);
//limit ?,? 
c.setFirstResult(0);
c.setMaxResults(2);

List<Customer> list = c.list();

System.out.println(list); 

排序

Criteria c = session.createCriteria(Customer.class);

c.addOrder(Order.asc("cust_id"));
//c.addOrder(Order.desc("cust_id"));

List<Customer> list = c.list();

System.out.println(list);

统计

Criteria c = session.createCriteria(Customer.class);

//设置查询目标
c.setProjection(Projections.rowCount());

List list = c.list();

System.out.println(list);

离线查询

非离线

离线

演示

@Test
public void fun1(){
    //Service/web层
    DetachedCriteria dc  = DetachedCriteria.forClass(Customer.class);
    
    dc.add(Restrictions.idEq(6l));//拼装条件(全部与普通Criteria一致)
    
    //----------------------------------------------------
    Session session = HibernateUtils.openSession();
    Transaction tx = session.beginTransaction();
    //----------------------------------------------------
    Criteria c = dc.getExecutableCriteria(session);
    
    List list = c.list();
    
    System.out.println(list);
    //----------------------------------------------------
    tx.commit();
    session.close();
    
}

查询优化

类级别查询

get方法:没有任何策略.调用即立即查询数据库加载数据.

load方法: 应用类级别的加载策略

Customer.hbm.xml中配置

<class name="Customer" table="cst_customer" lazy="false">

lazy(默认值):true, 查询类时,会返回代理对象.会在使用属性时,根据关联的session查询数据库.加载数据.

lazy:false. load方法会与get方法没有任何区别.调用时即加载数据.

结论:为了提高效率.建议使用延迟加载(懒加载)

注意:使用懒加载时要确保,调用属性加载数据时,session还是打开的.不然会抛出异常

关联级别查询

集合策略

<!-- 
lazy属性: 决定是否延迟加载
    true(默认值): 延迟加载,懒加载
    false: 立即加载
    extra: 极其懒惰
fetch属性: 决定加载策略.使用什么类型的sql语句加载集合数据
    select(默认值): 单表查询加载
    join: 使用多表查询加载集合
    subselect:使用子查询加载集合
-->

关联属性策略

<!-- 
fetch 决定加载的sql语句
    select: 使用单表查询
    join : 多表查询
lazy  决定加载时机
    false: 立即加载
    proxy: 由customer的类级别加载策略决定.
 -->

结论:为了提高效率.fetch的选择上应选择select. lazy的取值应选择 true. 全部使用默认值.

no-session问题解决: 扩大session的作用范围.

批量抓取

<!-- batch-size: 抓取集合的数量为3.
             抓取客户的集合时,一次抓取几个客户的联系人集合.
-->

练习:为客户列表增加查询条件