HQL简单用法
总共涉及到四个类：
(1)Category.java
package edu.smc.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;
}
}
(2)Topic.java
package edu.smc.hibernate;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
@Entity
public class Topic {
private int id;
private String title;
private Category category;
@Id
@GeneratedValue
public int getId() {
return id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public Category getCategory() {
return category;
}
public void setCategory(Category category) {
this.category = category;
}
public void setId(int id) {
this.id = id;
}
@ManyToOne
public Category getCatetory() {
return category;
}
public void setCatetory(Category catetory) {
this.category = category;
}
}
(3)Msg.java
package edu.smc.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;
public String getCont() {
return cont;
}
public void setCont(String cont) {
this.cont = cont;
}
private Topic topic;
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
@ManyToOne
public Topic getTopic() {
return topic;
}
public void setTopic(Topic topic) {
this.topic = topic;
}
}
(4)MsgInfo.java
package edu.smc.hibernate;
public class MsgInfo {
private int id;
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;
}
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;
}
private String cont;
private String topicName;
private String categoryName;
public MsgInfo(int id,String cont,String topicName,String categoryName){
this.id=id;
this.cont=cont;
this.topicName=topicName;
this.categoryName=categoryName;
}
}
1.取出所有的Category对象 .
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Category");
List categories = (List)q.list();
for(Category c : categories) {
System.out.println(c.getName());
}
session.getTransaction().commit();
session.close(); 2.取出Category.name>c5 的对象
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Category c where c.name > 'c5'");
List categories = (List)q.list();
for(Category c : categories) {
System.out.println(c.getName());
}
session.getTransaction().commit();
session.close();
3.取出所有Category对象，并用Category.name进行倒序排序
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Category c order by c.name desc");
List categories = (List)q.list();
for(Category c : categories) {
System.out.println(c.getName());
}
session.getTransaction().commit();
session.close();
4.取出id大约参数min并且小于参数max的Category对象
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Category c where c.id > :min and c.id < :max")
.setInteger("min", 2)
.setInteger("max", 8);
List categories = (List)q.list();
for(Category c : categories) {
System.out.println(c.getId() + "-" + c.getName());
}
session.getTransaction().commit();
session.close();
5.取出id在某两个数之间的Category对象（预处理方式）
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Category c where c.id > ? and c.id < ?");
q.setParameter(0, 2)
.setParameter(1, 8);
List categories = (List)q.list();
for(Category c : categories) {
System.out.println(c.getId() + "-" + c.getName());
}
session.getTransaction().commit();
session.close();
6.分页
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Category c order by c.name desc");
q.setMaxResults(4); /*设置每页最多的记录数*/
q.setFirstResult(2);/*设置从那一条记录开始取*/
List categories = (List)q.list();
for(Category c : categories) {
System.out.println(c.getId() + "-" + c.getName());
}
session.getTransaction().commit();
session.close(); 7.值取出 Category对象的 name,id 并且按照name进行降序排序
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("select c.id, c.name from Category c order by c.name desc");
List categories = (List)q.list();
for(Object[] o : categories) {
System.out.println(o[0] + "-" + o[1]);
}
session.getTransaction().commit();
session.close(); 8.取出Catetory id为1的Topic对象
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Topic t where t.category.id = 1");
List topics = (List)q.list();
for(Topic t : topics) {
System.out.println(t.getTitle());
}
session.getTransaction().commit();
session.close();
9.取出Category id为1的 Topic下的Msg对象
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Msg m where m.topic.category.id = 1");
for(Object o : q.list()) {
Msg m = (Msg)o;
System.out.println(m.getCont());
}
session.getTransaction().commit();
session.close();
10.取出一些数据组成一个新的对象（VO,DTO）
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("select new edu.smc.hibernate.MsgInfo(m.id, m.cont, m.topic.title, m.topic.category.name) from Msg");
for(Object o : q.list()) {
MsgInfo m = (MsgInfo)o;
System.out.println(m.getCont());
}
session.getTransaction().commit();
session.close();
11.Join的写法
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("select t.title, c.name from Topic t join t.category c ");
/** 不能直接写Category名，而必须写t.category,因为有可能存在多个成员变量（属于一个类），需要指明用哪一个成员变量的连接条件来做连接*/
for(Object o : q.list()) {
Object[] m = (Object[])o;
System.out.println(m[0] + "-" + m[1]);
}
session.getTransaction().commit();
session.close();
12.使用uniqueResult方法（当确定返回的实例只有一个或者null时 用uniqueResult()方法）
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Msg m where m = :MsgToSearch "); /*这里是对象相等*/
Msg m = new Msg();
m.setId(1);
q.setParameter("MsgToSearch", m); /*设置参数为 Msg对象*/
Msg mResult = (Msg)q.uniqueResult(); /*使用 Query 的 uniqueResult()方法*/
System.out.println(mResult.getCont());
session.getTransaction().commit();
session.close();
13 .获取总个数
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("select count(*) from Msg m");
long count = (Long)q.uniqueResult();
System.out.println(count);
session.getTransaction().commit();
session.close();
14.max , min ,avg, sum的用法
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("select max(m.id), min(m.id), avg(m.id), sum(m.id) from Msg m");
Object[] o = (Object[])q.uniqueResult();
System.out.println(o[0] + "-" + o[1] + "-" + o[2] + "-" + o[3]);
session.getTransaction().commit();
session.close();
15. between....and
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Msg m where m.id between 3 and 5");
for(Object o : q.list()) {
Msg m = (Msg)o;
System.out.println(m.getId() + "-" + m.getCont());
}
session.getTransaction().commit();
session.close();16.集合的用法
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Msg m where m.id in (3,4, 5)");
for(Object o : q.list()) {
Msg m = (Msg)o;
System.out.println(m.getId() + "-" + m.getCont());
}
session.getTransaction().commit();
session.close();17. is not null
Session session = sf.openSession();
session.beginTransaction();
Query q = session.createQuery("from Msg m where m.cont is not null");
for(Object o : q.list()) {
Msg m = (Msg)o;
System.out.println(m.getId() + "-" + m.getCont());
}
session.getTransaction().commit();
session.close();18.empty
Session session = sf.openSession();
session.beginTransaction();
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();
19.like( % 代表一个或多个，_ 代表一个)
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(); 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();20.内置函数（不常用）
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(); 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(); Session session = sf.openSession(); /*日期，时间，时间戳*/
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();21.日期比较
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();22.分组 Having
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();23.子查询
Session session = sf.openSession();
session.beginTransaction();
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();24.关键字ALL的使用
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();25.Exist(可用in实现exist的功能，exist的效率更高，所以一般选用exist)
Session session = sf.openSession();
session.beginTransaction();// t.id not in (1)
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();26.更新
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();27.命名查询（便于集中管理）
在类中写
@NamedQueries(
{
@NamedQuery(name="topic.selectCertainTopic", query="from Topic t where t.id = :id")
}
)
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();28.Native SQL
Session session = sf.openSession();
session.beginTransaction();
SQLQuery q = session.createSQLQuery("select * from category limit 2,4").addEntity(Category.class);
List categories = (List)q.list();
for(Category c : categories) {
System.out.println(c.getName());
}
session.getTransaction().commit();
session.close();
注：HQL 应该和导航相结合，共同为查询提供服务。