HQL查询语言的作用是什么
本篇文章为大家展示了HQL查询语言的作用是什么，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。
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1.获取Hibernate Session对象
2.编写HQL语句
3.以HQL语句作为参数，调用Session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独享的list()或uniqueResult()方法返回查询结果列表
简单的例子：
复制代码 代码如下:
@SuppressWarnings("deprecation")
public class HibernateUtil {
private static final SessionFactory sessionFactory;
static {
sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
}
public static Session getOpenSession() {
return sessionFactory.openSession();
}
public static Session getCurrentSession() {
return sessionFactory.getCurrentSession();
}
}
@Entity
public class Employee {
private Integer id;
private String name;
private Integer age;
@Id
@GeneratedValue
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
@Basic
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Basic
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String toString() {
return "id:" + id + " " + "name:" + name + " " + "age:" + age;
}
}
@SuppressWarnings("all")
public class HQLDemo {
@Test
public void testHQL() {
Session session = HibernateUtil.getOpenSession();
List
for(Employee e : employeeList)
System.out.println(e);
}
@Test
public void testHQLHasParameter() {
Session session = HibernateUtil.getOpenSession();
List
for(Employee e : employeeList)
System.out.println(e);
}
}
HQL查询的from子句：
from是最简单的HQL语句，也是最基本的HQL语句，from关键字后紧跟持久化类的类名，如：
from Employee表名从Employee类中选出全部的实例
不过我们常用的是这样做：
from employee as e这个e就是Employee的别名，也就是实例名，推荐这么写。
HQL查询的select子句：
select子句用于选择指定的属性或直接选择某个实体，当然select选择的属性必须是from后持久化类包含的属性，如：
select e.name from Employee as e select可以选择任意属性，即不仅可以选择持久化类的直接属性，还可以选择组件属性包含的属性，如：
select e.name.firstName from Employee as eHQL查询的聚集函数：
聚集函数：
avg：计算属性的平均值
count：统计选择对象的数量
max：统计属性值的最大值
min：统计属性值的最小值
sum：计算属性值的总和
如：
复制代码 代码如下:
select count(*) from Employee as e @Test
public void testHQLFunction() {
Session session = HibernateUtil.getOpenSession();
System.out.println(session.createQuery("select count(*) from Employee as e").uniqueResult());
}
多态查询：
HQL不仅会查询出该持久化类的全部实例，还会查询出该类的子类的全部实例，前提是存在继承映射。
HQL查询的where子句：
where子句主要用于筛选选中的结果，缩小选择的范围，如：
复制代码 代码如下:
from employee as e where e.name like "xjg%" @Test
public void testHQLWhere() {
Session session = HibernateUtil.getOpenSession();
List
for(Employee e : employeeList)
System.out.println(e);
}
order by子句：
查询返回结合可以根据类或组件属性的任何属性进行排序，还可以使用asc或desc关键字指定升序或者降序，如：
from Employee as e order by e.name desc
子查询：
子查询中就是查询语句中还有查询语句，如：
复制代码 代码如下:
from Employee as e where e.age > (select p.age from Person as p) @Test
public void testHQLChildQuery() {
Session session = HibernateUtil.getOpenSession();
List
for(Employee e : employeeList)
System.out.println(e);
}
[code]
命名查询：
HQL查询还支持将查询所用的HQL语句放入配置文件中，而不是代码中，在Hibernate映射文件的
[code]
from Employee as e
Session里提供了一个getNamedQuery(String name)方法，该方法用于创建一个Query对象，一旦获得Query对象，剩下的工作就跟前面的一样了。
复制代码 代码如下:
@Test
public void testHQLNamedQuery() {
Session session = HibernateUtil.getOpenSession();
List
for(Employee e : employeeList)
System.out.println(e);
}
HQL 查询语句
/**
*
*/
package com.b510.example;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import org.hibernate.Criteria;
import org.hibernate.FetchMode;
import org.hibernate.Query;
import org.hibernate.Session;
/**
*
* @author XHW
*
* @date 2011-6-18
*
*/
public class HibernateTest {
/**
* @param args
*/
public static void main(String[] args) {
HibernateTest test = new HibernateTest();
test.where();
test.function();
test.update();
test.jiaoChaCheck();
test.innerJoin();
test.QBC();
test.leftOuterJoin();
test.rightOuterJoin();
}
public void where() {
// 使用where查询
Session session = HibernateSessionFactoryUtil.getSessionFactory()
.openSession();
session.beginTransaction();
Query query = session
.createQuery("from User where id not between 200 and 2000");
List
for (User user : list) {
System.out.println(user.getId() + user.getUsername());
}
// 投影查询 中使用where子句
query = session.createQuery("select username from User where id=2");
List
for (String name : listname) {
System.out.println(name);
}
// in查询
query = session
.createQuery("from User where username in ('Hongten','Hanyuan','dfgd')");
List
for (User user : listin) {
System.out.println(user.getId() + user.getUsername());
}
// like查询
query = session.createQuery("from User where username not like 'Hon%'");
List
for (User user : listlike) {
System.out.println(user.getId() + user.getUsername());
}
// null查询
query = session.createQuery("from User where password is null");
List
for (User user : listnull) {
System.out.println(user.getId() + user.getUsername());
}
// and查询
query = session
.createQuery("from User where password is not null and id<5");
List
for (User user : listand) {
System.out.println(user.getId() + user.getUsername()
+ user.getPassword());
}
// order by
query = session.createQuery("from User order by username,id desc");
List
for (User user : listorderby) {
System.out.println(user.getId() + user.getUsername());
}
// 使用"?"号 作为参数占位符，一条HQL语句中可以使用多个？
// query.setInteger(0,2)
// query.setString(0,"Hongten")
query = session
.createQuery("select username from User where username=?");
query.setString(0, "Hongten");
List
for (String name : listwenhao) {
System.out.println(name);
}
session.getTransaction().commit();
}
public void function() {// 把大写字母转化为小写字母
// 作用可以用在：比如在一个用户注册的程序中，大小写不容易区分，但是全部转化为小写后就可以很容易进行比较
Session session = HibernateSessionFactoryUtil.getSessionFactory()
.openSession();
session.beginTransaction();
// 输出原始的数据
Query query = session.createQuery("select username from User");
List
for (String name : list) {
System.out.println(name);
}
System.out.println("-------------------------------------------");
// 输出的数据全部转化为小写
query = session.createQuery("select lower(username) from User");
List
for (String name : listChange) {
System.out.println(name);
}
session.getTransaction().commit();
}
public void update() {
Session session = HibernateSessionFactoryUtil.getSessionFactory()
.openSession();
session.beginTransaction();
Query query = session
.createQuery("update User set username='洪伟1231' where id=?");
query.setInteger(0, 3);
int rowCount = query.executeUpdate();
System.out.println(rowCount);
session.getTransaction().commit();
}
public void operateProfile() {// 对profile这个类执行HQL语句操作
Session session = HibernateSessionFactoryUtil.getSessionFactory()
.openSession();
session.beginTransaction();
// 执行查询操作
Query query = session.createQuery("from Profile");
List
for (Profile profile : list) {
System.out.println(profile.getId() + profile.getEmail()
+ profile.getAddress() + profile.getMobile()
+ profile.getPostcode());
}
// 执行删除操作
query = session.createQuery("delete from Profile where id=?");
query.setInteger(0, 3);
int rowCount = query.executeUpdate();
System.out.println(rowCount);
session.getTransaction().commit();
}
public void jiaoChaCheck() {//交叉查询
//这种方法查询出来的结果是笛卡尔积，对于我们开发中没有多大用处
Session session = HibernateSessionFactoryUtil.getSessionFactory()
.openSession();
session.beginTransaction();
Query query=session.createQuery("from User,Profile");
List
for(Object[] values:list){
User user=(User)values[0];
System.out.print("ID :"+user.getId()+",UserName:"+user.getUsername()+",Password:"+user.getPassword());
Profile profile=(Profile)values[1];
System.out.println(profile.getEmail()+profile.getMobile()+profile.getAddress()+profile.getPostcode());
}
session.getTransaction().commit();
}
public void innerJoin(){//内连接查询
/**
* 下面三种hql语句都是可以得到相同的结果
* String hql="select p from Profile as p inner join p.user";
* 在下面的hql语句中加入"fetch"后，此hql语句变为了"迫切HQL"语句，这样的查询效率要比上面的hql语句要高
* String hql="select p from Profile as p inner join fetch p.user";
*
* String hql="select p from Profile p,User u where p.user=u";
* String hql="select p from Profile p,User u where p.user.id=u.id";
*
*/
Session session = HibernateSessionFactoryUtil.getSessionFactory()
.openSession();
session.beginTransaction();
String hql="select p from Profile as p inner join fetch p.user";
//String hql="select p from Profile p,User u where p.user=u";
//String hql="select p from Profile p,User u where p.user.id=u.id";
Query query=session.createQuery(hql);
List
for(Profile p:list){
System.out.println("ID:"+p.getUser().getId()+" Username: "+p.getUser().getUsername()+" Email: "+p.getEmail()+", Address: "+p.getAddress());
}
session.getTransaction().commit();
}
public void QBC(){//QBC中实现内连接查询
Session session=HibernateSessionFactoryUtil.getSessionFactory().openSession();
session.beginTransaction();
Criteria criteria=session.createCriteria(Profile.class).createCriteria("user");
List
for(Profile p:list){
System.out.println("ID:"+p.getUser().getId()+" Username: "+p.getUser().getUsername()+" Email: "+p.getEmail()+", Address: "+p.getAddress());
}
//QBC中实现外连接
System.out.println("##################################################");
criteria=session.createCriteria(Profile.class).setFetchMode("user", FetchMode.JOIN);
List
for(Profile p:list){
System.out.println("ID:"+p.getUser().getId()+" Username: "+p.getUser().getUsername()+" Email: "+p.getEmail()+", Address: "+p.getAddress());
}
session.getTransaction().commit();
}
public void leftOuterJoin(){//左外连接
/**
* String hql="select p from Profile p left outer join p.user order by p.user.id";
* 在下面的hql语句中加入"fetch"后，此hql语句变为了"迫切HQL"语句，这样的查询效率要比上面的hql语句要高
* String hql="select p from Profile p left outer join fetch p.user order by p.user.id";
*
* String hqlu="select u from User u left outer join u.profiles";
* 在下面的hql语句中加入"fetch"后，此hql语句变为了"迫切HQL"语句，这样的查询效率要比上面的hql语句要高
* String hqlu="select u from User u left outer join fetch u.profiles";
*/
Session session=HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();
String hql="select p from Profile p left outer join fetch p.user order by p.user.id";
Query query=session.createQuery(hql);
List
for(Profile p:list){
System.out.println("ID:"+p.getUser().getId()+" Username: "+p.getUser().getUsername()+" Email: "+p.getEmail()+", Address: "+p.getAddress());
}
System.out.println("-------------------------------------");
String hqlu="select u from User u left outer join fetch u.profiles";
query=session.createQuery(hqlu);
List
for(User u:listu){
System.out.println(u.getId()+u.getUsername()+u.getProfiles());
}
session.getTransaction().commit();
}
public void rightOuterJoin(){//右外连接
Session session=HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();
String hql="select u from User u right outer join u.profiles order by u.id";
Query query=session.createQuery(hql);
List
for(User user:listu){
System.out.println(user.getId()+user.getUsername()+user.getProfiles());
}
session.getTransaction().commit();
}
}
结果：
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate:
select
user0_.id as id0_,
user0_.username as username0_,
user0_.password as password0_
from
users.user user0_
where
user0_.id not between 200 and 2000
1hongten
2hanyuan
3hongwei
4mingliu
5shouzhang
Hibernate:
select
user0_.username as col_0_0_
from
users.user user0_
where
user0_.id=2
hanyuan
Hibernate:
select
user0_.id as id0_,
user0_.username as username0_,
user0_.password as password0_
from
users.user user0_
where
user0_.username in (
'Hongten' , 'Hanyuan' , 'dfgd'
)
1hongten
2hanyuan
Hibernate:
select
user0_.id as id0_,
user0_.username as username0_,
user0_.password as password0_
from
users.user user0_
where
user0_.username not like 'Hon%'
2hanyuan
4mingliu
5shouzhang
Hibernate:
select
user0_.id as id0_,
user0_.username as username0_,
user0_.password as password0_
from
users.user user0_
where
user0_.password is null
Hibernate:
select
user0_.id as id0_,
user0_.username as username0_,
user0_.password as password0_
from
users.user user0_
where
(
user0_.password is not null
)
and user0_.id<5
1hongten123
2hanyuan5645645
3hongwei5645645
4mingliu5645645
Hibernate:
select
user0_.id as id0_,
user0_.username as username0_,
user0_.password as password0_
from
users.user user0_
order by
user0_.username,
user0_.id desc
2hanyuan
1hongten
3hongwei
4mingliu
5shouzhang
Hibernate:
select
user0_.username as col_0_0_
from
users.user user0_
where
user0_.username=?
hongten
Hibernate:
select
user0_.username as col_0_0_
from
users.user user0_
hongten
hanyuan
hongwei
mingliu
shouzhang
-------------------------------------------
Hibernate:
select
lower(user0_.username) as col_0_0_
from
users.user user0_
hongten
hanyuan
hongwei
mingliu
shouzhang
Hibernate:
update
users.user
set
username='Hongwei1231'
where
id=?
1
Hibernate:
select
user0_.id as id0_0_,
profile1_.id as id1_1_,
user0_.username as username0_0_,
user0_.password as password0_0_,
profile1_.user_id as user2_1_1_,
profile1_.email as email1_1_,
profile1_.phone as phone1_1_,
profile1_.mobile as mobile1_1_,
profile1_.address as address1_1_,
profile1_.postcode as postcode1_1_
from
users.user user0_,
users.profile profile1_
ID :1,UserName:hongten,Password:123hongtenzone@foxmail.com45464Guangzhoushi65465
ID :1,UserName:hongten,Password:123hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :1,UserName:hongten,Password:123hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :2,UserName:hanyuan,Password:5645645hongtenzone@foxmail.com45464Guangzhoushi65465
ID :2,UserName:hanyuan,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :2,UserName:hanyuan,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :3,UserName:Hongwei1231,Password:5645645hongtenzone@foxmail.com45464Guangzhoushi65465
ID :3,UserName:Hongwei1231,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :3,UserName:Hongwei1231,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :4,UserName:mingliu,Password:5645645hongtenzone@foxmail.com45464Guangzhoushi65465
ID :4,UserName:mingliu,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :4,UserName:mingliu,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :5,UserName:shouzhang,Password:5645645hongtenzone@foxmail.com45464Guangzhoushi65465
ID :5,UserName:shouzhang,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :5,UserName:shouzhang,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
Hibernate:
select
profile0_.id as id1_0_,
user1_.id as id0_1_,
profile0_.user_id as user2_1_0_,
profile0_.email as email1_0_,
profile0_.phone as phone1_0_,
profile0_.mobile as mobile1_0_,
profile0_.address as address1_0_,
profile0_.postcode as postcode1_0_,
user1_.username as username0_1_,
user1_.password as password0_1_
from
users.profile profile0_
inner join
users.user user1_
on profile0_.user_id=user1_.id
ID:1 Username: hongten Email: hongtenzone@foxmail.com, Address: Guangzhoushi
ID:2 Username: hanyuan Email: hanyuan@foxmail.com, Address: GuangzhoushiDianbian
ID:3 Username:Hongwei1231 Email: hanyuan@foxmail.com, Address: GuangzhoushiDianbian
Hibernate:
select
this_.id as id1_1_,
this_.user_id as user2_1_1_,
this_.email as email1_1_,
this_.phone as phone1_1_,
this_.mobile as mobile1_1_,
this_.address as address1_1_,
this_.postcode as postcode1_1_,
user1_.id as id0_0_,
user1_.username as username0_0_,
user1_.password as password0_0_
from
users.profile this_
inner join
users.user user1_
on this_.user_id=user1_.id
ID:1 Username: hongten Email: hongtenzone@foxmail.com, Address: Guangzhoushi
ID:2 Username: hanyuan Email: hanyuan@foxmail.com, Address: GuangzhoushiDianbian
ID:3 Username: Hongwei1231 Email: hanyuan@foxmail.com, Address: GuangzhoushiDianbian
##################################################
Hibernate:
select
this_.id as id1_1_,
this_.user_id as user2_1_1_,
this_.email as email1_1_,
this_.phone as phone1_1_,
this_.mobile as mobile1_1_,
this_.address as address1_1_,
this_.postcode as postcode1_1_,
user2_.id as id0_0_,
user2_.username as username0_0_,
user2_.password as password0_0_
from
users.profile this_
left outer join
users.user user2_
on this_.user_id=user2_.id
ID:1 Username: hongten Email: hongtenzone@foxmail.com, Address: Guangzhoushi
ID:2 Username: hanyuan Email: hanyuan@foxmail.com, Address: GuangzhoushiDianbian
ID:3 Username: 洪伟1231 Email: hanyuan@foxmail.com, Address: GuangzhoushiDianbian
Hibernate:
select
profile0_.id as id1_0_,
user1_.id as id0_1_,
profile0_.user_id as user2_1_0_,
profile0_.email as email1_0_,
profile0_.phone as phone1_0_,
profile0_.mobile as mobile1_0_,
profile0_.address as address1_0_,
profile0_.postcode as postcode1_0_,
user1_.username as username0_1_,
user1_.password as password0_1_
from
users.profile profile0_
left outer join
users.user user1_
on profile0_.user_id=user1_.id
order by
profile0_.user_id
ID:1 Username: hongten Email: hongtenzone@foxmail.com, Address: Guangzhoushi
ID:2 Username: hanyuan Email: hanyuan@foxmail.com, Address: GuangzhoushiDianbian
ID:3 Username: 洪伟1231 Email: hanyuan@foxmail.com, Address: GuangzhoushiDianbian
-------------------------------------
Hibernate:
select
user0_.id as id0_0_,
profiles1_.id as id1_1_,
user0_.username as username0_0_,
user0_.password as password0_0_,
profiles1_.user_id as user2_1_1_,
profiles1_.email as email1_1_,
profiles1_.phone as phone1_1_,
profiles1_.mobile as mobile1_1_,
profiles1_.address as address1_1_,
profiles1_.postcode as postcode1_1_,
profiles1_.user_id as user2_0__,
profiles1_.id as id0__
from
users.user user0_
left outer join
users.profile profiles1_
on user0_.id=profiles1_.user_id
1hongten[com.b510.example.Profile@14eaec9]
2hanyuan[com.b510.example.Profile@569c60]
3Hongwei1231[com.b510.example.Profile@d67067]
4mingliu[]
5shouzhang[]
Hibernate:
select
user0_.id as id0_,
user0_.username as username0_,
user0_.password as password0_
from
users.user user0_
right outer join
users.profile profiles1_
on user0_.id=profiles1_.user_id
order by
user0_.id
Hibernate:
select
profiles0_.user_id as user2_1_,
profiles0_.id as id1_,
profiles0_.id as id1_0_,
profiles0_.user_id as user2_1_0_,
profiles0_.email as email1_0_,
profiles0_.phone as phone1_0_,
profiles0_.mobile as mobile1_0_,
profiles0_.address as address1_0_,
profiles0_.postcode as postcode1_0_
from
users.profile profiles0_
where
profiles0_.user_id=?
1hongten[com.b510.example.Profile@10c0f66]
Hibernate:
select
profiles0_.user_id as user2_1_,
profiles0_.id as id1_,
profiles0_.id as id1_0_,
profiles0_.user_id as user2_1_0_,
profiles0_.email as email1_0_,
profiles0_.phone as phone1_0_,
profiles0_.mobile as mobile1_0_,
profiles0_.address as address1_0_,
profiles0_.postcode as postcode1_0_
from
users.profile profiles0_
where
profiles0_.user_id=?
2hanyuan[com.b510.example.Profile@e265d0]
Hibernate:
select
profiles0_.user_id as user2_1_,
profiles0_.id as id1_,
profiles0_.id as id1_0_,
profiles0_.user_id as user2_1_0_,
profiles0_.email as email1_0_,
profiles0_.phone as phone1_0_,
profiles0_.mobile as mobile1_0_,
profiles0_.address as address1_0_,
profiles0_.postcode as postcode1_0_
from
users.profile profiles0_
where
profiles0_.user_id=?
3Hongwei1231[com.b510.example.Profile@8997d1]
上述内容就是HQL查询语言的作用是什么，你们学到知识或技能了吗？如果还想学到更多技能或者丰富自己的知识储备，欢迎关注创新互联行业资讯频道。
分享题目：HQL查询语言的作用是什么
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