【hibernate框架】EJBQL第二部分
工程和上一个一样，Topic有所改变，加了一个Topic的Msg的List列表属性，这个属性用来存放每个Topic下有多少条回帖。
例子项目：BBS小项目
（EJBQL是HQL的子集，所以直接说是HQL也无可厚非）
Category(版块)：里面有不同的主题，不同的主题有不同的发帖
Topic(主题)，Msg(具体的回复帖子)
Category与Topic之间的关系是一对多(OneToMany)，Topic与Msg的关系也是一对多。(OneToMany)。
具体的类：
Category.java:
Topic.java:
Msg.java:
MsgInfo.java:
各种测试：
测试结果：
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
not (exists (select //用了exists
msgs1_.id
from
Msg msgs1_
where
topic0_.id=msgs1_.topic_id))
2-t1
3-t2
4-t3
5-t4
6-t5
7-t6
8-t7
9-t8
10-t9
找到了没有任何回帖的主题(想得到msgs就得加一个一对多的导航)
is Null是测试一个属性空不空，is empty是测试一个集合空不空
——————————————————————————————————————
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
topic0_.title like '%5'
6-t5
其中，‘%’代表0个或多个，‘_’代表一个
——————————————————————————————————————
测试结果：
Hibernate:
select
lower(topic0_.title) as col_0_0_,
upper(topic0_.title) as col_1_0_,
trim(topic0_.title) as col_2_0_,
concat(topic0_.title,
'***') as col_3_0_,
length(topic0_.title) as col_4_0_
from
Topic topic0_
t0-T0-t0-t0***-2-
t1-T1-t1-t1***-2-
t2-T2-t2-t2***-2-
t3-T3-t3-t3***-2-
t4-T4-t4-t4***-2-
t5-T5-t5-t5***-2-
t6-T6-t6-t6***-2-
t7-T7-t7-t7***-2-
t8-T8-t8-t8***-2-
t9-T9-t9-t9***-2-
函数测试2：
Hibernate:
select
abs(topic0_.id) as col_0_0_,
sqrt(topic0_.id) as col_1_0_,
mod(topic0_.id,
2) as col_2_0_
from
Topic topic0_
1-1.0-1
2-1.4142135623730951-0
3-1.7320508075688772-1
4-2.0-0
5-2.23606797749979-1
6-2.449489742783178-0
7-2.6457513110645907-1
8-2.8284271247461903-0
9-3.0-1
10-3.1622776601683795-0
——————————————————————————————————————
数据库的一些关键词
current_date指的是数据库当前日期，current_time指的是数据库当前时间, current_timestamp指的是数据库当前日期和时间。
测试结果：
Hibernate:
select
current_date as col_0_0_,
current_time as col_1_0_,
current_timestamp as col_2_0_,
topic0_.id as col_3_0_
from
Topic topic0_
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 1
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 2
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 3
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 4
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 5
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 6
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 7
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 8
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 9
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 10
什么时候用到获取数据库的时间呢？
我直接取我程序里面的时间不就可以了吗？干嘛非要取数据库的时间呢？
因为在一个集群化的环境中，会有多台服务器围绕一个数据库来进行服务，如果你的日期需要在多台服务器上保持一致的话，你用服务器的时间能保持一致吗？肯定会有误差，但是我都用唯一的一台数据库的时间就不会有误差了。
——————————————————————————————————————
关于日期的比较:
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
topic0_.createDate<?
t0
t1
t2
t3
t4
t5
t6
t7
t8
t9
——————————————————————————————————————
select
topic0_.title as col_0_0_,
count(*) as col_1_0_
from
Topic topic0_
group by
topic0_.title
t0|1
t1|1
t2|1
t3|1
t4|1
t5|1
t6|1
t7|1
t8|1
t9|1：
测试二：
Hibernate:
select
topic0_.title as col_0_0_,
count(*) as col_1_0_
from
Topic topic0_
group by
topic0_.title
having
count(*)>=1
t0|1
t1|1
t2|1
t3|1
t4|1
t5|1
t6|1
t7|1
t8|1
t9|1
——————————————————————————————————————
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
topic0_.id<(
select
avg(topic1_.id)
from
Topic topic1_
)
t0
t1
t2
t3
t4
一共10个id，(1+2+3+4+5+6+7+8+9+10)/10=5.5，所以取出的是小于5的id的title。
——————————————————————————————————————
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
topic0_.id<all (
select
topic1_.id
from
Topic topic1_
where
mod(topic1_.id, 2)=0
)
t0
——————————————————————————————————————
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
not (exists (select
msg1_.id
from
Msg msg1_
where
msg1_.topic_id=topic0_.id))
t1
t2
t3
t4
t5
t6
t7
t8
t9
——————————————————————————————————————
Hibernate:
update
Topic
set
title=upper(title)
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
T0
T1
T2
T3
T4
T5
T6
T7
T8
T9
Hibernate:
update
Topic
set
title=lower(title)
——————————————————————————————————————
测试结果:
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
topic0_.id=?
t4
——————————————————————————————————————
使用本地的SQL语句：
Hibernate:
select
*
from
category limit 2,
4
c2
c3
c4
c5
——————————————————————————————————————
转载请注明出处:http://blog.csdn.net/acmman/article/details/43917909
例子项目：BBS小项目
（EJBQL是HQL的子集，所以直接说是HQL也无可厚非）
Category(版块)：里面有不同的主题，不同的主题有不同的发帖
Topic(主题)，Msg(具体的回复帖子)
Category与Topic之间的关系是一对多(OneToMany)，Topic与Msg的关系也是一对多。(OneToMany)。
具体的类：
Category.java:
package com.bjsxt.hibernate;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
@Entity
public class Category {
private int id;
private String name;
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
Topic.java:
package com.bjsxt.hibernate;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
@Entity
@NamedQueries({
@NamedQuery(name="topic.selectCertainTopic", query="from Topic t where t.id = :id")})
public class Topic {
private int id;
private String title;
private Category category;
private Date createDate;
private List<Msg> msgs = new ArrayList<Msg>();
@OneToMany(mappedBy="topic")
public List<Msg> getMsgs() {
return msgs;
}
public void setMsgs(List<Msg> msgs) {
this.msgs = msgs;
}
@Temporal(TemporalType.TIME)
public Date getCreateDate() {
return createDate;
}
public void setCreateDate(Date createDate) {
this.createDate = createDate;
}
@ManyToOne(fetch=FetchType.LAZY)
public Category getCategory() {
return category;
}
public void setCategory(Category category) {
this.category = category;
}
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
}
Msg.java:
package com.bjsxt.hibernate;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
@Entity
public class Msg {
private int id;
private String cont;
private Topic topic;
@ManyToOne
public Topic getTopic() {
return topic;
}
public void setTopic(Topic topic) {
this.topic = topic;
}
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getCont() {
return cont;
}
public void setCont(String cont) {
this.cont = cont;
}
}
MsgInfo.java:
package com.bjsxt.hibernate;
public class MsgInfo { //VO DTO Value Object username p1 p2 UserInfo->User->DB
private int id;
private String cont;
private String topicName;
private String categoryName;
public MsgInfo(int id, String cont, String topicName, String categoryName) {
super();
this.id = id;
this.cont = cont;
this.topicName = topicName;
this.categoryName = categoryName;
}
public String getTopicName() {
return topicName;
}
public void setTopicName(String topicName) {
this.topicName = topicName;
}
public String getCategoryName() {
return categoryName;
}
public void setCategoryName(String categoryName) {
this.categoryName = categoryName;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getCont() {
return cont;
}
public void setCont(String cont) {
this.cont = cont;
}
}
各种测试：
//is empty and is not empty
@Test
public void testHQL_20() {
Session session = sf.openSession();
session.beginTransaction();
//说t的Mags集合是否为空，即是寻找没有任何回帖的主题
Query q = session.createQuery("from Topic t where t.msgs is empty");
for(Object o : q.list()) {
Topic t = (Topic)o;
System.out.println(t.getId() + "-" + t.getTitle());
}
session.getTransaction().commit();
session.close();
}
测试结果：
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
not (exists (select //用了exists
msgs1_.id
from
Msg msgs1_
where
topic0_.id=msgs1_.topic_id))
2-t1
3-t2
4-t3
5-t4
6-t5
7-t6
8-t7
9-t8
10-t9
找到了没有任何回帖的主题(想得到msgs就得加一个一对多的导航)
is Null是测试一个属性空不空，is empty是测试一个集合空不空
——————————————————————————————————————
@Test
public void testHQL_21() {
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Topic t where t.title like '%5'");
for(Object o : q.list()) {
Topic t = (Topic)o;
System.out.println(t.getId() + "-" + t.getTitle());
}
session.getTransaction().commit();
session.close();
}测试结果：
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
topic0_.title like '%5'
6-t5
其中，‘%’代表0个或多个，‘_’代表一个
——————————————————————————————————————
//不重要(使用HQL语句里面的一些函数)
@Test
public void testHQL_23() {
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("select lower(t.title)," +
"upper(t.title)," +
"trim(t.title)," +
"concat(t.title, '***')," +
"length(t.title)" +
" from Topic t ");
for(Object o : q.list()) {
Object[] arr = (Object[])o;
System.out.println(arr[0] + "-" + arr[1] + "-" + arr[2] + "-" + arr[3] + "-" + arr[4] + "-");
}
session.getTransaction().commit();
session.close();
}
测试结果：
Hibernate:
select
lower(topic0_.title) as col_0_0_,
upper(topic0_.title) as col_1_0_,
trim(topic0_.title) as col_2_0_,
concat(topic0_.title,
'***') as col_3_0_,
length(topic0_.title) as col_4_0_
from
Topic topic0_
t0-T0-t0-t0***-2-
t1-T1-t1-t1***-2-
t2-T2-t2-t2***-2-
t3-T3-t3-t3***-2-
t4-T4-t4-t4***-2-
t5-T5-t5-t5***-2-
t6-T6-t6-t6***-2-
t7-T7-t7-t7***-2-
t8-T8-t8-t8***-2-
t9-T9-t9-t9***-2-
函数测试2：
@Test
public void testHQL_24() {
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("select abs(t.id)," +
"sqrt(t.id)," +
"mod(t.id, 2)" +
" from Topic t ");
for(Object o : q.list()) {
Object[] arr = (Object[])o;
System.out.println(arr[0] + "-" + arr[1] + "-" + arr[2] );
}
session.getTransaction().commit();
session.close();
}测试结果：
Hibernate:
select
abs(topic0_.id) as col_0_0_,
sqrt(topic0_.id) as col_1_0_,
mod(topic0_.id,
2) as col_2_0_
from
Topic topic0_
1-1.0-1
2-1.4142135623730951-0
3-1.7320508075688772-1
4-2.0-0
5-2.23606797749979-1
6-2.449489742783178-0
7-2.6457513110645907-1
8-2.8284271247461903-0
9-3.0-1
10-3.1622776601683795-0
——————————————————————————————————————
数据库的一些关键词
@Test
public void testHQL_25() {
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("select current_date, current_time, current_timestamp, t.id from Topic t");
for(Object o : q.list()) {
Object[] arr = (Object[])o;
System.out.println(arr[0] + " | " + arr[1] + " | " + arr[2] + " | " + arr[3]);
}
session.getTransaction().commit();
session.close();
}
current_date指的是数据库当前日期，current_time指的是数据库当前时间, current_timestamp指的是数据库当前日期和时间。
测试结果：
Hibernate:
select
current_date as col_0_0_,
current_time as col_1_0_,
current_timestamp as col_2_0_,
topic0_.id as col_3_0_
from
Topic topic0_
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 1
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 2
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 3
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 4
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 5
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 6
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 7
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 8
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 9
2015-02-01 | 15:59:53 | 2015-02-01 15:59:53.0 | 10
什么时候用到获取数据库的时间呢？
我直接取我程序里面的时间不就可以了吗？干嘛非要取数据库的时间呢？
因为在一个集群化的环境中，会有多台服务器围绕一个数据库来进行服务，如果你的日期需要在多台服务器上保持一致的话，你用服务器的时间能保持一致吗？肯定会有误差，但是我都用唯一的一台数据库的时间就不会有误差了。
——————————————————————————————————————
关于日期的比较:
@Test
public void testHQL_26() {
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Topic t where t.createDate < :date");
q.setParameter("date", new Date());
for(Object o : q.list()) {
Topic t = (Topic)o;
System.out.println(t.getTitle());
}
session.getTransaction().commit();
session.close();
}测试结果：
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
topic0_.createDate<?
t0
t1
t2
t3
t4
t5
t6
t7
t8
t9
——————————————————————————————————————
//group by语句用于结合合计函数，根据一个或多个列对结果集进行分组
//你的group by后面的属性一定要在前面的select里面。
@Test
public void testHQL_27() {
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("select t.title, count(*) from Topic t group by t.title") ;
for(Object o : q.list()) {
Object[] arr = (Object[])o;
System.out.println(arr[0] + "|" + arr[1]);
}
session.getTransaction().commit();
session.close();
}测试结果Hibernate:
select
topic0_.title as col_0_0_,
count(*) as col_1_0_
from
Topic topic0_
group by
topic0_.title
t0|1
t1|1
t2|1
t3|1
t4|1
t5|1
t6|1
t7|1
t8|1
t9|1：
测试二：
@Test
public void testHQL_28() {
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("select t.title, count(*) from Topic t group by t.title having count(*) >= 1") ;
for(Object o : q.list()) {
Object[] arr = (Object[])o;
System.out.println(arr[0] + "|" + arr[1]);
}
session.getTransaction().commit();
session.close();
}测试结果：
Hibernate:
select
topic0_.title as col_0_0_,
count(*) as col_1_0_
from
Topic topic0_
group by
topic0_.title
having
count(*)>=1
t0|1
t1|1
t2|1
t3|1
t4|1
t5|1
t6|1
t7|1
t8|1
t9|1
——————————————————————————————————————
@Test
public void testHQL_29() {
Session session = sf.openSession();
session.beginTransaction();
//取平均值，看哪些数据小于这些平均值
Query q = session.createQuery("from Topic t where t.id < (select avg(t.id) from Topic t)") ;
for(Object o : q.list()) {
Topic t = (Topic)o;
System.out.println(t.getTitle());
}
session.getTransaction().commit();
session.close();
}测试结果：
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
topic0_.id<(
select
avg(topic1_.id)
from
Topic topic1_
)
t0
t1
t2
t3
t4
一共10个id，(1+2+3+4+5+6+7+8+9+10)/10=5.5，所以取出的是小于5的id的title。
——————————————————————————————————————
//ALL函数，就是满足ALL后条件内的所有值(其实找极端值就可以了呗)
@Test
public void testHQL_30() {
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Topic t where t.id < ALL (select t.id from Topic t where mod(t.id, 2)= 0) ") ;
for(Object o : q.list()) {
Topic t = (Topic)o;
System.out.println(t.getTitle());
}
session.getTransaction().commit();
session.close();
}测试结果:
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
topic0_.id<all (
select
topic1_.id
from
Topic topic1_
where
mod(topic1_.id, 2)=0
)
t0
——————————————————————————————————————
//用in 可以实现exists的功能
//但是exists执行效率高
@Test
public void testHQL_31() {
Session session = sf.openSession();
session.beginTransaction();// t.id not in (1)
//括号里的意思是msg表里面存在不存在属于某个topic的msg(总的意思是找哪个topic下面没有回帖)
Query q = session.createQuery("from Topic t where not exists (select m.id from Msg m where m.topic.id=t.id)") ;
// Query q = session.createQuery("from Topic t where exists (select m.id from Msg m where m.topic.id=t.id)") ;
for(Object o : q.list()) {
Topic t = (Topic)o;
System.out.println(t.getTitle());
}
session.getTransaction().commit();
session.close();
}测试结果：
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
not (exists (select
msg1_.id
from
Msg msg1_
where
msg1_.topic_id=topic0_.id))
t1
t2
t3
t4
t5
t6
t7
t8
t9
——————————————————————————————————————
//update and delete
//规范并没有说明是不是要更新persistent object，所以如果要使用，建议在单独的trasaction中执行
@Test
public void testHQL_32() {
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("update Topic t set t.title = upper(t.title)") ;
q.executeUpdate();
q = session.createQuery("from Topic");
for(Object o : q.list()) {
Topic t = (Topic)o;
System.out.println(t.getTitle());
}
session.createQuery("update Topic t set t.title = lower(t.title)")
.executeUpdate();
session.getTransaction().commit();
session.close();
}
测试结果：
Hibernate:
update
Topic
set
title=upper(title)
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
T0
T1
T2
T3
T4
T5
T6
T7
T8
T9
Hibernate:
update
Topic
set
title=lower(title)
——————————————————————————————————————
//不重要
getNamedQuery方法拿到命名查询，这个命名查询写在实体类的上面
测试方法：
@Test
public void testHQL_33() {
Session session = sf.openSession();
session.beginTransaction();
Query q = session.getNamedQuery("topic.selectCertainTopic");
q.setParameter("id", 5);
Topic t = (Topic)q.uniqueResult();
System.out.println(t.getTitle());
session.getTransaction().commit();
session.close();
}实体类部分代码：
package com.bjsxt.hibernate;
import java.util.ArrayList;
@Entity
@NamedQueries({
@NamedQuery(name="topic.selectCertainTopic", query="from Topic t where t.id = :id")})
public class Topic {........
测试结果:
Hibernate:
select
topic0_.id as id2_,
topic0_.category_id as category4_2_,
topic0_.createDate as createDate2_,
topic0_.title as title2_
from
Topic topic0_
where
topic0_.id=?
t4
——————————————————————————————————————
使用本地的SQL语句：
//Native（了解）
@Test
public void testHQL_34() {
Session session = sf.openSession();
session.beginTransaction();
SQLQuery q = session.createSQLQuery("select * from category limit 2,4").addEntity(Category.class);
List<Category> categories = (List<Category>)q.list();
for(Category c : categories) {
System.out.println(c.getName());
}
session.getTransaction().commit();
session.close();
}测试结果：
Hibernate:
select
*
from
category limit 2,
4
c2
c3
c4
c5
——————————————————————————————————————
转载请注明出处:http://blog.csdn.net/acmman/article/details/43917909