Hibernate的HQL简介详解编程语言

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>