Hiberante框架学习（二）_customer customer1 = session.load(customer.class, -优快云博客

本文链接：https://blog.youkuaiyun.com/zhangjun62/article/details/89218888

Hibernate的查询的方式

OID查询

OID检索 Hibernate根据对象的OID（主键）进行检索

使用get方法 Customer customer = session.get(Customer.class,1l);

使用load方法 Customer customer = session.load(Customer.class,1l);

对象导航检索

对象导航检索 Hibernate根据一个已经查询到的对象，获得其关联的对象的一种查询方式。

LinkMan linkMan = session.get(LinkMan.class,1l);

Customer customer = linkMan.getCustomer();

Customer customer = session.get(Customer.class,2l);

Set<LinkMan> linkMans = customer.getLinkMans();

HQL检索

HQL查询：Hibernate Query Language，Hibernate的查询语言，是一种面向对象的方式的查询语言，语法类似SQL。通过session.createQuery()，用于接收一个HQL进行查询方式。

简单查询

Session session = HibernateUtil.getCurrentSession();
Transaction transaction = session.beginTransaction();
Query query = session.createQuery("from Customer");
List<Customer> list = query.list();
//SQL支持*号的写法 select * from cst_customer;HQL不支持
//Query query = session.createQuery("select * from Customer");//报错
//List<Customer> list = query.list();
for (Customer customer : list) {
    System.out.println(customer);
}
transaction.commit();

别名查询

Session session = HibernateUtil.getCurrentSession();
Transaction transaction = session.beginTransaction();
Query query = session.createQuery("select c from Customer c");
List<Customer> list = query.list();

for (Customer customer : list) {
    System.out.println(customer);
}
transaction.commit();

排序查询

Session session = HibernateUtil.getCurrentSession();
Transaction transaction = session.beginTransaction();
//默认情况
//List<Customer> list = session.createQuery("from Customer order by cust_id").list();
//设置降序排序 升序使用asc 降序使用desc
List<Customer> list = session.createQuery("from Customer order by cust_id desc").list();

for (Customer customer : list) {
    System.out.println(customer);
}
transaction.commit();

条件查询

Session session = HibernateUtil.getCurrentSession();
Transaction transaction = session.beginTransaction();
//按位置绑定
//一个条件
/*
Query query = session.createQuery("from Customer where cust_name = ?");
query.setParameter(0,"张飞");
List<Customer> list = query.list();
*/
//多个条件
/*
Query query = session.createQuery("from Customer where cust_source = ? and cust_name like ?");
query.setParameter(0, "小广告");
query.setParameter(1,"张%");
List<Customer> list = query.list();
*/
//按名称绑定
Query query = session.createQuery("from Customer where cust_source = :aaa and cust_name like :bbb");
query.setParameter("aaa", "网络推广");
query.setParameter("bbb","张%");
List<Customer> list = query.list();
for (Customer customer : list) {
    System.out.println(customer);
}
transaction.commit();

投影查询

投影查询查询对象的某个或某些属性。

Session session = HibernateUtil.getCurrentSession();
Transaction transaction = session.beginTransaction();
//单个属性
/*
List<Object> list = session.createQuery("select c.cust_name from Customer c").list();
for (Object object : list){
    System.out.println(object);
}
*/
//多个属性
/*
List<Object[]> list = session.createQuery("select c.cust_name, c.cust_source from Customer c").list();
for (Object[] objects : list){
    System.out.println(Arrays.toString(objects));
}
*/
//多个属性封装到对象中，需提供无参和有参构造方法
List<Customer> list = session.createQuery("select new Customer(c.cust_name, c.cust_source) from Customer c").list();
for (Customer customer : list) {
    System.out.println(customer);
}
transaction.commit();

分页查询

Session session = HibernateUtil.getCurrentSession();
Transaction transaction = session.beginTransaction();
Query query = session.createQuery("from LinkMan");
query.setFirstResult(10);
query.setMaxResults(10);
List<LinkMan> list = query.list();
for (LinkMan linkMan : list) {
    System.out.println(linkMan);
}
transaction.commit();

分组统计查询

Session session = HibernateUtil.getCurrentSession();
Transaction transaction = session.beginTransaction();
//count(),max(),min(),avg(),sum()
/*
Query query = session.createQuery("select count(*) from Customer");
Long sum = (Long)query.uniqueResult();
System.out.println(sum);
*/
Query query = session.createQuery("select cust_source, count(*) from Customer group by cust_source having count(*) > 1");
List<Object[]> list = query.list();
for (Object[] objects : list){
    System.out.println(Arrays.toString(objects));
}

transaction.commit();

多表查询

SQL的多表查询

连接查询

交叉连接笛卡尔积

select * from A,B;

内连接 :inner join (inner 可以省略)

隐式内连接

select * from A,B where A.id = B.aid;

显示内连接

select * from A inner join B on A.id = B.aid;

外连接

左外连接:left outer join(outer 可以省略)