本文共 10509 字，大约阅读时间需要 35 分钟。

HQL

HQL是HIbernate Query Language 的缩写，提供更加丰富灵活、更为强大的查询能力；HQL更接近SQL语句查询语法。

Hibernate查询语言（HQL）是一种面向对象的查询语言，类似与SQL，但不是去对表和列进行操作，而是面向对象和它们的属性。HQL查询被Hibernate翻译为传统的SQL查询从而对数据库进行操作。

$注意：除了Java类与属性名称外，查询语句对大小写不敏感。当有相同的实体类名时，必须使用包名.类名。$

HQL查询的步骤：

1. 获得HibernateSession对象
2. 编写HQL语句
3. 调用Sesison的createQuery方法创建查询对象
4. 如果HQL语句包含参数，则调用Query的setXxx方法为参数赋值
5. 调用Query对象的list等方法返回查询结果。

准备工作

创建一个Customer实体类

package pers.zhang.domain;public class Customer {
   	private Long cust_id;	private String cust_name;	private String cust_source;	private String cust_industry;	private String cust_level;	private String cust_linkman;	private String cust_phone;	private String cust_mobile;		public Long getCust_id() {
   		return cust_id;	}	public void setCust_id(Long cust_id) {
   		this.cust_id = cust_id;	}	public String getCust_name() {
   		return cust_name;	}	public void setCust_name(String cust_name) {
   		this.cust_name = cust_name;	}	public String getCust_source() {
   		return cust_source;	}	public void setCust_source(String cust_source) {
   		this.cust_source = cust_source;	}	public String getCust_industry() {
   		return cust_industry;	}	public void setCust_industry(String cust_industry) {
   		this.cust_industry = cust_industry;	}	public String getCust_level() {
   		return cust_level;	}	public void setCust_level(String cust_level) {
   		this.cust_level = cust_level;	}	public String getCust_linkman() {
   		return cust_linkman;	}	public void setCust_linkman(String cust_linkman) {
   		this.cust_linkman = cust_linkman;	}	public String getCust_phone() {
   		return cust_phone;	}	public void setCust_phone(String cust_phone) {
   		this.cust_phone = cust_phone;	}	public String getCust_mobile() {
   		return cust_mobile;	}	public void setCust_mobile(String cust_mobile) {
   		this.cust_mobile = cust_mobile;	}	@Override	public String toString() {
   		return "Customer [cust_id=" + cust_id + ", cust_name=" + cust_name + "]";	}}

配置ORM元数据：

准备数据：

基本查询–返回List

• HQL查询的from语句
  如果你想要在存储中加载一个完整并持久的对象,你将使用FROM语句。Hibernate中最简单的查询语句的形式如下：
  from pers.zhang.Customer
  该自居简单的返回Customer类的所有实例。通常我们不需要使用类的全限定名，因为auto-import(自动引入)是缺省的情况。所以我们几乎只使用如下的简单写法：
  from Customer
• HQL查询的AS 语句
  大多数情况下，需要指定一个别名，原因是可能需要在查询语句的其他部分引用到Customer：
  from Customer as c
  这个语句把别名c指定给类Customer的实例，这样就可以在随后的查询中使用此别名了。关键字as是可选的，所以也可以这样写：
  from Customer c

例子：

@Test	//基本查询	public void fun1(){
   		//获得session		Session session = HibernateUtils.openSession();		//控制事务		Transaction tx = session.beginTransaction();		//3执行操作		//-------------------------------------------		//书写HQL语句		//String hql = " from cn.itheima.domain.Customer ";		String hql = " from Customer c"; // 查询所有Customer对象		//根据HQL语句创建查询对象		Query query = session.createQuery(hql);		//根据查询对象获得查询结果		List
   
     list = query.list();	// 返回list结果				System.out.println(list);		//-------------------------------------------		//4提交事务.关闭资源		tx.commit();		session.close();	}
   

运行JUnit测试输出：

Hibernate:     select        customer0_.cust_id as cust_id1_0_,        customer0_.cust_name as cust_nam2_0_,        customer0_.cust_source as cust_sou3_0_,        customer0_.cust_industry as cust_ind4_0_,        customer0_.cust_level as cust_lev5_0_,        customer0_.cust_linkman as cust_lin6_0_,        customer0_.cust_phone as cust_pho7_0_,        customer0_.cust_mobile as cust_mob8_0_     from        cst_customer customer0_        [Customer [cust_id=1, cust_name=Google],  Customer [cust_id=2, cust_name=联想], Customer [cust_id=3, cust_name=百度],  Customer [cust_id=4, cust_name=阿里巴巴],  Customer [cust_id=5, cust_name=腾讯]]

条件查询–返回唯一对象或List

如果想要精准的从数据库存储中返回特定对象，需要使用where语句。在where字句中允许使用的表达式包括大多数可以在SQL中使用的表达式种类：

• 数学运算符+,-,*,/
• 二进制比较运算符=,>=,<=,<>,!=,like
• 逻辑运算符and,or,not
• in, not in, between, is null, is not null, is empty, is not empty, member of and not member of
• “简单的” case, case … when … then … else … end, 和“搜索” case, case when … then … else … end
• 字符串连接符… || … or concat(…,…)
• current_date(), current_time(), current_timestamp()
• second(…),minute(…),hour(…),day(…),month(…),year(…)
• EJB-QL 3.0 定义的任何函数或操作：substring(),trim(),lower(),upper(),length(),locate(),abs(),sqrt(),bit_length()
• coalesce()和nullif()
• cast(… as …)， 其第二个参数是某Hibernate类型的名字，以及extract(… from …),只要ANSI cast() 和 extract() 被底层数据库支持
• JDBC参数传入?
• 命名参数：name，start_date, :xl
• SQL 直接常量 ‘foo’, 69, ‘1970-01-01 10:00:01.0’
• Java public static final 类型常量

关键字in与between可按如下方法使用：

from Customer c where c.cust_name between ‘A’ and ‘B’ from Customer c where c.cust_name in (‘Google’, ‘百度’) 而且否定的格式也可以如下书写： from Customer c where c.cust_name not between ‘A’ and ‘B’ from Customer c where c.cust_name not in (‘Google’, ‘百度’)

例子：

@Test	//条件查询	//HQL语句中,不可能出现任何数据库相关的信息的	public void fun2(){
   		//1 获得session		Session session = HibernateUtils.openSession();		//2 控制事务		Transaction tx = session.beginTransaction();		//3执行操作		//-------------------------------------------		//书写HQL语句,条件查询		String hql1 = " from Customer where cust_id = 1 "; 		String hql2 = "from Customer c where c.cust_name in ('Google', '百度', '联想')";		//2根据HQL语句创建查询对象		Query query1 = session.createQuery(hql1);		Query query2 = session.createQuery(hql2);		//3根据查询对象获得查询结果		Customer c1 = (Customer) query1.uniqueResult();		List
   
     list = query2.list();				System.out.println(c1);		System.out.println(list);		//-------------------------------------------		//4提交事务.关闭资源		tx.commit();		session.close();	}
   

运行JUnit测试输出：

Hibernate:     select        customer0_.cust_id as cust_id1_0_,        customer0_.cust_name as cust_nam2_0_,        customer0_.cust_source as cust_sou3_0_,        customer0_.cust_industry as cust_ind4_0_,        customer0_.cust_level as cust_lev5_0_,        customer0_.cust_linkman as cust_lin6_0_,        customer0_.cust_phone as cust_pho7_0_,        customer0_.cust_mobile as cust_mob8_0_     from        cst_customer customer0_     where        customer0_.cust_id=1Hibernate:     select        customer0_.cust_id as cust_id1_0_,        customer0_.cust_name as cust_nam2_0_,        customer0_.cust_source as cust_sou3_0_,        customer0_.cust_industry as cust_ind4_0_,        customer0_.cust_level as cust_lev5_0_,        customer0_.cust_linkman as cust_lin6_0_,        customer0_.cust_phone as cust_pho7_0_,        customer0_.cust_mobile as cust_mob8_0_     from        cst_customer customer0_     where        customer0_.cust_name in (            'Google' , '百度' , '联想'        )Customer [cust_id=1, cust_name=Google][Customer [cust_id=1, cust_name=Google], Customer [cust_id=2, cust_name=联想], Customer [cust_id=3, cust_name=百度]]

条件查询–？占位符

在HQL语句中使用?占位符，然后根据索引和类型使用setXxx方法设置参数。

$setXxx（index,arg）中index从0开始，与SQL的从1开始不同！$ 例子：

@Test	//条件查询	//问号占位符	public void fun3(){
   		//1 获得session		Session session = HibernateUtils.openSession();		//2 控制事务		Transaction tx = session.beginTransaction();		//3执行操作		//-------------------------------------------		//书写HQL语句		String hql = " from Customer where cust_id = ? ";		//根据HQL语句创建查询对象		Query query = session.createQuery(hql);		//设置参数		//query.setLong(0, 1l);//指定类型		query.setParameter(0, 1l);//自动匹配类型		//根据查询对象获得查询结果		Customer c = (Customer) query.uniqueResult();				System.out.println(c);		//-------------------------------------------		//4提交事务.关闭资源		tx.commit();		session.close();	}

运行JUnit测试输出：

Hibernate:     select        customer0_.cust_id as cust_id1_0_,        customer0_.cust_name as cust_nam2_0_,        customer0_.cust_source as cust_sou3_0_,        customer0_.cust_industry as cust_ind4_0_,        customer0_.cust_level as cust_lev5_0_,        customer0_.cust_linkman as cust_lin6_0_,        customer0_.cust_phone as cust_pho7_0_,        customer0_.cust_mobile as cust_mob8_0_     from        cst_customer customer0_     where        customer0_.cust_id=?Customer [cust_id=1, cust_name=Google]

条件查询–命名占位符

命名占位符使用 “:” + “占位符名字” 的格式，随后使用query.setParameter(“占位符名字”, arg)来设置参数。

例子：

@Test	//条件查询	//命名占位符	public void fun4(){
   		//1 获得session		Session session = HibernateUtils.openSession();		//2 控制事务		Transaction tx = session.beginTransaction();		//3执行操作		//-------------------------------------------		//书写HQL语句		String hql = " from Customer where cust_id = :id ";		//根据HQL语句创建查询对象		Query query = session.createQuery(hql);		//设置参数		query.setParameter("id", 1l);		//根据查询对象获得查询结果		Customer c = (Customer) query.uniqueResult();				System.out.println(c);		//-------------------------------------------		//4提交事务.关闭资源		tx.commit();		session.close();	}

运行JUnit测试输出：

Hibernate:     select        customer0_.cust_id as cust_id1_0_,        customer0_.cust_name as cust_nam2_0_,        customer0_.cust_source as cust_sou3_0_,        customer0_.cust_industry as cust_ind4_0_,        customer0_.cust_level as cust_lev5_0_,        customer0_.cust_linkman as cust_lin6_0_,        customer0_.cust_phone as cust_pho7_0_,        customer0_.cust_mobile as cust_mob8_0_     from        cst_customer customer0_     where        customer0_.cust_id=?Customer [cust_id=1, cust_name=Google]

分页查询

HQL的分页查询与MySql的limit十分相似，使用两个方法：

1.query.setFirstResult(arg)，设置第一条结果从哪个索引开始，相当于limit中的第一个?。 2.query.setMaxResults(arg)，设置一次查询多少条数据，相遇于limit中的第二个？。 例子：

@Test	//分页查询	public void fun5(){
   		//1获得session		Session session = HibernateUtils.openSession();		//2控制事务		Transaction tx = session.beginTransaction();		//3执行操作		//-------------------------------------------		//书写HQL语句		String hql = " from Customer  "; // 查询所有Customer对象		//根据HQL语句创建查询对象		Query query = session.createQuery(hql);		//设置分页信息 limit ?,?		query.setFirstResult(1);		query.setMaxResults(2);		//据查询对象获得查询结果		List
   
     list =  query.list();				System.out.println(list);		//-------------------------------------------		//4提交事务.关闭资源		tx.commit();		session.close();	}
   

运行JUnit测试输出：

Hibernate:     select        customer0_.cust_id as cust_id1_0_,        customer0_.cust_name as cust_nam2_0_,        customer0_.cust_source as cust_sou3_0_,        customer0_.cust_industry as cust_ind4_0_,        customer0_.cust_level as cust_lev5_0_,        customer0_.cust_linkman as cust_lin6_0_,        customer0_.cust_phone as cust_pho7_0_,        customer0_.cust_mobile as cust_mob8_0_     from        cst_customer customer0_ limit ?,        ?[Customer [cust_id=2, cust_name=联想], Customer [cust_id=3, cust_name=百度]]

转载地址：http://bjsqb.baihongyu.com/