一、查询种类
1.oid查询-get
2.对象属性导航查询
3.HQL
4.Criteria
5.原生SQL
二、查询-HQL语法
//学习HQL语法
public class Demo { //基本语法
@Test
public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql = " from cn.itcast.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);
//----------------------------------------------------
tx.commit();
session.close(); } @Test
//排序
public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql1 = " from cn.itcast.domain.Customer order by cust_id asc ";//完整写法
String hql2 = " from cn.itcast.domain.Customer order by cust_id desc ";//完整写法 Query query = session.createQuery(hql2); List list = query.list(); System.out.println(list);
//----------------------------------------------------
tx.commit();
session.close(); } @Test
//条件查询
public void fun3(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql1 = " from cn.itcast.domain.Customer where cust_id =? ";//完整写法
String hql2 = " from cn.itcast.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);
//----------------------------------------------------
tx.commit();
session.close(); } @Test
//分页查询
public void fun4(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql1 = " from cn.itcast.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);
//----------------------------------------------------
tx.commit();
session.close(); } @Test
//统计查询
//count 计数
//sum 求和
//avg 平均数
//max
//min
public void fun5(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql1 = " select count(*) from cn.itcast.domain.Customer ";//完整写法
String hql2 = " select sum(cust_id) from cn.itcast.domain.Customer ";//完整写法
String hql3 = " select avg(cust_id) from cn.itcast.domain.Customer ";//完整写法
String hql4 = " select max(cust_id) from cn.itcast.domain.Customer ";//完整写法
String hql5 = " select min(cust_id) from cn.itcast.domain.Customer ";//完整写法 Query query = session.createQuery(hql5); Number number = (Number) query.uniqueResult(); System.out.println(number);
//----------------------------------------------------
tx.commit();
session.close(); } @Test
//投影查询
public void fun6(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql1 = " select cust_name from cn.itcast.domain.Customer ";
String hql2 = " select cust_name,cust_id from cn.itcast.domain.Customer ";
String hql3 = " select new Customer(cust_id,cust_name) from cn.itcast.domain.Customer "; Query query = session.createQuery(hql3); List list = query.list(); System.out.println(list); //----------------------------------------------------
tx.commit();
session.close(); }
}
学习HQL语法
public class Demo2 {
//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的多表查询
//内连接(迫切)
//外连接
// |-左外(迫切)
// |-右外(迫切)
@Test
//HQL 内连接 => 将连接的两端对象分别返回.放到数组中.
public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
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));
}
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//HQL 迫切内连接 => 帮我们进行封装.返回值就是一个对象
public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql = " from Customer c inner join fetch c.linkMens ";
Query query = session.createQuery(hql);
List<Customer> list = query.list();
System.out.println(list);
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//HQL 左外连接 => 将连接的两端对象分别返回.放到数组中.
public void fun3(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
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));
}
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//HQL 右外连接 => 将连接的两端对象分别返回.放到数组中.
public void fun4(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
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));
}
//----------------------------------------------------
tx.commit();
session.close();
}
}
学习HQL语法(不常用) - 多表查询语法
三、查询-Criteria语法
public class Demo {
@Test
//基本语法
public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
Criteria c = session.createCriteria(Customer.class);
List<Customer> list = c.list();
System.out.println(list);
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//条件语法
public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
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);
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//分页语法 - 与HQL一样
public void fun3(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
Criteria c = session.createCriteria(Customer.class);
//limit ?,?
c.setFirstResult(0);
c.setMaxResults(2);
List<Customer> list = c.list();
System.out.println(list);
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//排序语法
public void fun4(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
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);
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//统计语法
public void fun5(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
Criteria c = session.createCriteria(Customer.class);
//设置查询目标
c.setProjection(Projections.rowCount());
List list = c.list();
System.out.println(list);
//----------------------------------------------------
tx.commit();
session.close();
}
}
学习Criteria语法
非离线
离线
public class Demo2 {
@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();
}
}
学习离线Criteria
四、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
public class Demo {
@Test
// get方法 : 立即加载.执行方法时立即发送sql语句查询结果
public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
Customer c = session.get(Customer.class, 2l);
System.out.println(c);
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
// load方法(默认):是在执行时,不发送任何sql语句.返回一个对象.使用该对象时,才执行查询.
// 延迟加载: 仅仅获得没有使用.不会查询.在使用时才进行查询.
// 是否对类进行延迟加载: 可以通过在class元素上配置lazy属性来控制.
//lazy:true 加载时,不查询.使用时才查询b
//lazy:false 加载时立即查询.
public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
Customer c = session.load(Customer.class, 2l);
//----------------------------------------------------
tx.commit();
session.close();
System.out.println(c);
}
}
懒加载|延迟加载
public class Demo {
//集合级别的关联
//fetch:select 单表查询
//lazy:true 使用时才加载集合数据.
@Test
public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
Customer c = session.get(Customer.class, 2l);
Set<LinkMan> linkMens = c.getLinkMens();//关联级别
System.out.println(linkMens);
//----------------------------------------------------
tx.commit();
session.close();
}
//集合级别的关联
//fetch:select 单表查询
//lazy:false 立即记载集合数据
@Test
public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
Customer c = session.get(Customer.class, 2l);
Set<LinkMan> linkMens = c.getLinkMens();//关联级别
System.out.println(linkMens);
//----------------------------------------------------
tx.commit();
session.close();
}
//集合级别的关联
//fetch:select 单表查询
//lazy:extra 极其懒惰.与懒加载效果基本一致. 如果只获得集合的size.只查询集合的size(count语句)
@Test
public void fun3(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
Customer c = session.get(Customer.class, 2l);
Set<LinkMan> linkMens = c.getLinkMens();//关联级别
System.out.println(linkMens.size());
System.out.println(linkMens);
//----------------------------------------------------
tx.commit();
session.close();
}
//集合级别的关联
//fetch:join 多表查询
//lazy:true|false|extra 失效.立即加载.
@Test
public void fun4(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
Customer c = session.get(Customer.class, 2l);
Set<LinkMan> linkMens = c.getLinkMens();//关联级别
System.out.println(linkMens.size());
System.out.println(linkMens);
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//fetch: subselect 子查询
//lazy: true 懒加载
public void fun5(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql = "from Customer";
Query query = session.createQuery(hql);
List<Customer> list = query.list();
for(Customer c:list){
System.out.println(c);
System.out.println(c.getLinkMens().size());
System.out.println(c.getLinkMens());
}
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//fetch: subselect 子查询
//lazy: false 立即加载
public void fun6(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql = "from Customer";
Query query = session.createQuery(hql);
List<Customer> list = query.list();
for(Customer c:list){
System.out.println(c);
System.out.println(c.getLinkMens().size());
System.out.println(c.getLinkMens());
}
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//fetch: subselect 子查询
//lazy: extra 极其懒惰
public void fun7(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql = "from Customer";
Query query = session.createQuery(hql);
List<Customer> list = query.list();
for(Customer c:list){
System.out.println(c);
System.out.println(c.getLinkMens().size());
System.out.println(c.getLinkMens());
}
//----------------------------------------------------
tx.commit();
session.close();
}
}
关联级别 延迟加载 & 抓取策略（客户再获取多个联系人）
public class Demo2 {
@Test
//fetch:select 单表查询
//lazy:proxy
//customer-true 懒加载
public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
LinkMan lm = session.get(LinkMan.class, 3l);
Customer customer = lm.getCustomer();
System.out.println(customer);
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//fetch:join 多表
//lazy: 失效
public void fun3(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
LinkMan lm = session.get(LinkMan.class, 3l);
Customer customer = lm.getCustomer();
System.out.println(customer);
//----------------------------------------------------
tx.commit();
session.close();
}
@Test
//fetch:select 单表查询
//lazy:proxy
//customer-false 立即加载
public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
LinkMan lm = session.get(LinkMan.class, 3l);
Customer customer = lm.getCustomer();
System.out.println(customer);
//----------------------------------------------------
tx.commit();
session.close();
}
}
关联级别 延迟加载 & 抓取策略（通过联系人获得客户）
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.
public class Demo {
@Test
public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();
//----------------------------------------------------
String hql = "from Customer ";
Query query = session.createQuery(hql);
List<Customer> list = query.list();
for(Customer c:list){
System.out.println(c.getLinkMens());
}
//----------------------------------------------------
tx.commit();
session.close();
}
}
抓取数量
五、练习:为客户列表增加查询条件
在上一次笔记的代码基础上，在显示客户列表之前，加入筛选的条件:
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1获得查询条件
String cust_name = request.getParameter("cust_name");
//2判断查询条件是否不为空
DetachedCriteria dc = DetachedCriteria.forClass(Customer.class);
if(cust_name!=null && !"".equals(cust_name)){
dc.add(Restrictions.like("cust_name", "%"+cust_name+"%"));
}
//不为空=>添加条件
//3 调用Service查询所有客户
List<Customer> list = cs.getAll(dc);
//4 将客户列表放入request域
request.setAttribute("list", list);
//5 转发到list.jsp显示
request.getRequestDispatcher("/jsp/customer/list.jsp").forward(request, response);
}
Servlet层代码
public List<Customer> getAll(DetachedCriteria dc) {
Session session = HibernateUtils.getCurrentSession();
//打开事务
Transaction tx = session.beginTransaction();
List<Customer> list = customerDao.getAll(dc);
//关闭事务
tx.commit();
return list;
}
Service层代码
public List<Customer> getAll(DetachedCriteria dc) {
//1 获得session
Session session = HibernateUtils.getCurrentSession();
//2 将离线对象关联到session
Criteria c = dc.getExecutableCriteria(session);
//3 执行查询并返回
return c.list();
}
Dao层代码