hibernate_检索方式

 所谓的检索方式就是查询的方式。其中查询的方式有以下几种：

<1>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

<2>OID 检索方式:  按照对象的 OID 来检索对象
get()/load();方法进行检索.

<3>HQL 检索方式: 使用面向对象的 HQL 查询语言
Query query = session.createQuery(“HQL”);

<4>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);

<5>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”);

1. HQL查询
 HQL（Hibernate Query Language） 的特点是：面向对象查询、支持方法链。使用要创建Query接口。

<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);
         */

        /*
         * List<Object[]> list = session.createQuery(
         * "select c.cid,c.cname from Customer c").list(); for (Object[] objects
         * : list) { System.out.println(Arrays.toString(objects)); }
         */

        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);

SQL多表查询:
* 连接:
* 交叉连接:
* select * from A,B;
* 内连接:查询的是两个表的交集!
* 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:
* 连接:
* 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:

* HQL的内连接和迫切内连接区别:
* 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.

2. QBC（Query By Criteria）

<1>查询所有
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);

3. SQL

//SQL语句查询所有记录:
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);
        }