Hibernate的HQL简介

HQL（Hibernate Query Language）描写对象操作一种查询语言。Hibernate特有。
与SQL语法基本一致，不同的是HQL是面象对象的查询，查询的是对象和对象中的属性
HQL的关键字不区分大小写，但类名和属性名区分大小写

在Hibernate 提供的各种检索方式中, HQL是使用最广的一种检索方式. 它有如下功能:
在查询语句中设定各种查询条件
支持投影查询, 即仅检索出对象的部分属性
支持分页查询
支持连接查询
支持分组查询, 允许使用 HAVING 和 GROUP BY 关键字
提供内置聚集函数, 如 sum(), min() 和 max()
能够调用 用户定义的 SQL 函数或标准的 SQL 函数
支持子查询
支持动态绑定参数

测试类：

package com.my.bean;import java.util.List;import org.hibernate.Query;import org.hibernate.Session;import org.hibernate.Transaction;import org.junit.Test;import cn.itcast.util.SessionUtils;public class TestHQL {    @Test    public void demo01(){        // 查询所有 HQL        Session session = SessionUtils.openSession();        Transaction transaction = session.beginTransaction();        Query query = session.createQuery("from Customer");        List<Customer> allCustomer = query.list();         for (Customer customer : allCustomer) {            System.out.println(customer.getName());        }        transaction.commit();        session.close();    }    @Test    public void demo02(){        // 查询 带有条件的，可以使用别名 AS        Session session = SessionUtils.openSession();        Transaction transaction = session.beginTransaction();        Query query = session.createQuery("FROM Customer AS c WHERE c.id = 5");          Customer customer =  (Customer) query.uniqueResult();        System.out.println(customer.getName());        transaction.commit();        session.close();    }    @Test    public void demo03(){        // 排序 order by ， asc 升序 | desc 降序        Session session = SessionUtils.openSession();        Transaction transaction = session.beginTransaction();        Query query = session.createQuery("from Customer c order by c.id desc");        List<Customer> all = query.list();        for (Customer customer : all) {            System.out.println(customer);        }        transaction.commit();        session.close();    }    @Test    public void demo04(){        // 查询部分内容        Session session = SessionUtils.openSession();        Transaction transaction = session.beginTransaction();        //将部分数据，封装到Customer 对象中        Query query = session.createQuery("select new Customer(c.name) from Customer c");  //必须提供相应的构造方式        List all = query.list();        System.out.println(all);        transaction.commit();        session.close();    }    @Test    public void demo05(){        // 分页，查询订单        Session session = SessionUtils.openSession();        Transaction transaction = session.beginTransaction();        Query query = session.createQuery("from Order");        // 添加分页条件        // 第一页        query.setFirstResult(0);        query.setMaxResults(7);        List<Order> all = query.list();        for (Order order : all) {            System.out.println(order);        }        transaction.commit();        session.close();    }    @Test    public void demo06(){        // 参数        Session session = SessionUtils.openSession();        Transaction transaction = session.beginTransaction();        //使用？        Query query = session.createQuery("from Customer c where c.id = ? ");        // 需要绑定参数，将实际参数替换?        query.setParameter(0, 5);        List<Customer> all = query.list();        for (Customer customer : all) {            System.out.println(customer);        }        //* 使用hibernate提供的别名        Query query1 = session.createQuery("from Customer c where c.id = :id ");        query1.setInteger("id", 5); //第一个参数就是hql中定义名称   :名称        List<Customer> all = query1.list();        for (Customer customer : all) {            System.out.println(customer);        }        transaction.commit();        session.close();    }    @Test    public void demo07(){        // 聚合函数        Session session = SessionUtils.openSession();        Transaction transaction = session.beginTransaction();        // 使用hibernate提供的别名        Query query = session.createQuery("select count(*) from Customer");        Object obj = query.uniqueResult();        Long totalPage = (Long) obj;        transaction.commit();        session.close();    }    @Test    public void demo08(){        // 左外连接 -- left outer join        Session session = SessionUtils.openSession();        Transaction transaction = session.beginTransaction();        //* 使用hibernate提供的别名        Query query = session.createQuery("from Customer c left outer join c.orderSet");        // List 保存数据为 List ,数组中每一个元素又一个对象数组Object[],存放的是Customer，存放是Order        List<Object[]> all = query.list();        for (Object[] objArr : all) {            System.out.println(objArr);            //objArr[0] --> Customer            //objArr[1] --> Order        }        transaction.commit();        session.close();    }    @Test    public void demo09(){        // 迫切左外连接 -- left outer join fetch  ， 将数据封装到对象        Session session = SessionUtils.openSession();        Transaction transaction = session.beginTransaction();        //* 使用hibernate提供的别名  , 使用 distinct进行去重        Query query = session.createQuery("select distinct c from Customer c left outer join fetch c.orderSet");        List<Customer> all = query.list();        for (Customer customer : all) {            System.out.println(customer);        }        transaction.commit();        session.close();    }    @Test    public void demo10(){        // 命名查询        Session session = SessionUtils.openSession();        Transaction transaction = session.beginTransaction();        Query query = session.getNamedQuery("findAllCustomer"); //获得配置文件中的名称        System.out.println(query.list().size());        transaction.commit();        session.close();    }}

命名查询的hbm文件配置：

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.my.bean">    <class name="Customer" table="t_customer">        <id name="id">            <generator class="native"></generator>        </id>        <property name="name"></property>        <set name="orderSet" cascade="save-update">            <key column="customer_id"/>            <one-to-many class="Order"/>        </set>    </class>    <!-- 定义全局的HQL语句 -->    <query name="findAllCustomer">        <![CDATA[from Customer]]>     </query></hibernate-mapping>