Hibernate的检索方式

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Hibernate的检索方式
  检索方式(查询的方式
    导航对象图检索方式: 根据已经加载的对象导航到其他对象
      Customer customer = (Customer)session.get(Customer.class,1);
      customer.getOrders();// 获得到客户的订单
    OID 检索方式: 按照对象的 OID 来检索对象
      get()/load();方法进行检索.
    HQL 检索方式: 使用面向对象的 HQL 查询语言
      Query query = session.createQuery(“HQL”);
    QBC 检索方式: 使用 QBC(Query By Criteria) API 来检索对象. 这种 API 封装了基于字符串形式的查询语句, 提供了更加面向对象的查询接口.
      Criteria criteria = session.createCriteria(Customer.class);
    本地 SQL 检索方式: 使用本地数据库的 SQL 查询语句
      SQLQuery query = session.createSQLQuery(“SQL”);
HQL
  HQL:Hibernate Query Language
    特点:面向对象的查询,支持方法链编程
  1.查询所有记录

List<Customer> list = session.createQuery("from Customer").list();
for (Customer customer : list) {
  System.out.println(customer);
}

  2.查询使用别名

// 使用别名,别名as可以省略
List<Customer> list =session.createQuery("from Customer c").list();
System.out.println(list);
// 使用别名:带参数
List<Customer> list = session.createQuery("from Customer as c where c.cname = ?").setString(0, "小沈").list();
System.out.println(list);
// 不支持 select * from Customer写法.可以写成 select 别名 from Customer as 别名;
List<Customer> list = session.createQuery("select c from Customer c").list();
System.out.println(list);

  3.排序

List<Customer> list = session.createQuery("from Customer c order by c.id desc").list();
for (Customer customer : list) {
  System.out.println(customer);
}

  4.分页查询

Query query = session.createQuery("from Order");
query.setFirstResult(20);
query.setMaxResults(10);
List<Order> list = query.list();
for (Order order : list) {
  System.out.println(order);
}

  5.单个对象查询

Customer customer = (Customer) session.createQuery("from Customer where cname = ?").setString(0, "小明").uniqueResult();
System.out.println(customer);

  6.参数绑定

// 1.使用?号方式绑定
Query query = session.createQuery("from Customer where cname = ?");
query.setString(0, "小沈");
List<Customer> list = query.list();
System.out.println(list);

Query query = session.createQuery("from Customer where cname = ? and cid =?");
query.setString(0, "小沈");
query.setInteger(1,3);
List<Customer> list = query.list();
System.out.println(list);
// 2.使用名称的方式绑定 Query query = session.createQuery("from Customer where cname=:name and cid=:id"); query.setString("name", "小沈"); query.setInteger("id", 3); List<Customer> list = query.list(); System.out.println(list); // 3.绑定实体 List<Order> list = session.createQuery("from Order o where o.customer = ?").setEntity(0, customer).list(); for (Order order : list) {   System.out.println(order); }

  7.投影操作

// 查询客户的名称
List<Object> list = session.createQuery("select c.cname from Customer c").list(); 
System.out.println(list);
//查两个属性
List<Object[]> list = session.createQuery("select c.cid,c.cname from Customer c").list();
for (Object[] objects: list) { 
  System.out.println(Arrays.toString(objects)); 
}
//需要提供适当的构造方法
List<Customer> list = session.createQuery("select new Customer(cname) from Customer").list();
System.out.println(list);

  8.模糊查询

Query query = session.createQuery("from Customer where cname like ?");
query.setParameter(0, "小%");
List<Customer> list = query.list();
System.out.println(list);    

  9.聚集函数

Long count = (Long) session.createQuery("select count(*) from Order").uniqueResult();
System.out.println(count);    

  10.命名查询(在配置文件中配置查询语句)

List<Customer> list = session.getNamedQuery("findAll").list();
System.out.println(list);

  SQL多表查询(连接)
    交叉连接(用得少):select * from A,B
    内连接(自然连接):select * from A inner join B on A.字段 = B.字段;
    隐式内连接:select * from A,B where A.字段 = B.字段;
    外连接
      左外连接:select * from A left outer join B on A.字段 = B.字段;
      右外连接:select * from A right outer join B on A.字段 = B.字段;
  HQL多表的查询
    交叉连接,内连接,隐式内连接,迫切内连接,左外连接,迫切左外连接,右外连接
    隐式内连接(了解)
      createQuery("from Order o where o.customer.name like \'T%\'");
      等价于:from Order o join o.customer c where c.name like \'T%\'
    HQL的内连接和迫切内连接区别(其他类似):
      内连接查询 :将数据封装一个List<Object[]>中.
      迫切内连接 :将数据封装一个List<Customer>中.但是迫切内连接,得到会有重复记录 ,需要使用distinct排重.

// 内连接查询:
Query query = session.createQuery("from Customer c inner join c.orders");
List<Object[]> list = query.list();
for (Object[] objects : list) {
  Customer c = (Customer)objects[0];
  Order o = (Order)objects[1];
  System.out.println(c.getCid()+" "+c.getCname()+" "+c.getAge());
  System.out.println(o.getOid()+" "+o.getAddr());
}
// 迫切内连接:使用一个关键字 fetch(HQL)
Query query = session.createQuery("select distinct c from Customer c inner join fetch c.orders");
List<Customer> list = query.list();
for (Customer customer : list) {
  System.out.println(customer);
}

QBC
  1.查询所有记录

List<Customer> list = session.createCriteria(Customer.class).list();
for (Customer customer : list) {
  System.out.println(customer);
}

  2.排序

List<Customer> list = session.createCriteria(Customer.class).addOrder(org.hibernate.criterion.Order.desc("id")).list();
for (Customer customer : list) {
  System.out.println(customer);
}

  3.分页

Criteria criteria = session.createCriteria(Order.class);
criteria.setFirstResult(10);
criteria.setMaxResults(10);
List<Order> list = criteria.list();
for (Order order : list) {
  System.out.println(order);
}

  4.获取单个对象

Customer customer = (Customer) session.createCriteria(Customer.class).add(Restrictions.eq("cname", "小明")).uniqueResult();
System.out.println(customer);

  5.带参数的查询

List<Customer> list = session.createCriteria(Customer.class).add(Restrictions.eq("cname", "小明")).list();
System.out.println(list);

List<Customer> list = session.createCriteria(Customer.class).add(Restrictions.eq("cname", "小明")).add(Restrictions.eq("cid", 2)).list();
System.out.println(list);

  6.模糊查询

Criteria criteria = session.createCriteria(Customer.class);
criteria.add(Restrictions.like("cname", "大%"));
List<Customer> list = criteria.list();
System.out.println(list);

SQL

List<Object[]> list = session.createSQLQuery("select * from customer").list();
for (Object[] objects : list) {
  System.out.println(Arrays.toString(objects));
}
List<Customer> list = session.createSQLQuery("select * from customer").addEntity(Customer.class).list();
for (Customer customer : list) {
  System.out.println(customer);
}

离线查询
  

@Test
/*
* 离线条件查询
*/
public void demo(){
  // web层的封装
  DetachedCriteria criteria = DetachedCriteria.forClass(Customer.class);
  criteria.add(Restrictions.eq("cname", "小明"));
  criteria.add(Restrictions.eq("cid", 2));
  // 传递到DAO层
  Session session = HibernateUtils.openSession();
  Transaction tx = session.beginTransaction();
  Criteria c1 = criteria.getExecutableCriteria(session);
  List<Customer> list = c1.list();
  System.out.println(list);
  tx.commit();
  session.close();
}

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