11.hibernate的连接查询

1.创建如下javaweb项目结构

2.在项目的src下创建hibernate.cfg.xml主配置文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd" >
 3 <hibernate-configuration>
 4   <session-factory>
 5     <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
 6     <property name="connection.url">jdbc:oracle:thin:@127.0.0.1:1521:orcl</property>
 7     <property name="connection.username">scott</property>
 8     <property name="connection.password">tiger</property>
 9     <property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>
10     <property name="show_sql">true</property>
11     <property name="format_sql">true</property>
12     <mapping resource="com/entity/Dept.hbm.xml"/>
13     <mapping resource="com/entity/Emp.hbm.xml"/>
14   </session-factory>
15 </hibernate-configuration>

hibernate.cfg.xml

3.在项目的src下的com.util包下创建HibernateUtil.java

 1 package com.util;
 2 
 3 import org.hibernate.HibernateException;
 4 import org.hibernate.Session;
 5 import org.hibernate.SessionFactory;
 6 import org.hibernate.cfg.Configuration;
 7 
 8 public class HibernateUtil {
 9     private static ThreadLocal<Session> thread=new ThreadLocal<Session>();
10     private static Configuration config=null;
11     private static SessionFactory factory=null;
12     /**
13      * 读取配置文件
14      */
15     static{
16         try {
17             config=new Configuration().configure("/hibernate.cfg.xml");
18             factory=config.buildSessionFactory();
19         } catch (HibernateException e) {
20             System.out.println("读取配置文件失败或创建factory失败");
21             e.printStackTrace();
22         }
23     }
24     /**
25      * 打开session
26      * @return
27      */
28     public static Session getSession(){
29         Session session =thread.get();
30         if(session==null){
31             session=factory.openSession();
32             thread.set(session);
33         }
34         return session;
35     }
36     /**
37      * 关闭session
38      */
39     public static void closeSession(){
40         Session session =thread.get();
41         thread.set(null);
42         session.close();
43         
44     }
45 
46 }

HibernateUtil.java

4.在项目的src下的com.entity包下创建Dept.java

 1 package com.entity;
 2 
 3 import java.util.HashSet;
 4 import java.util.Set;
 5 
 6 public class Dept {
 7     private Integer deptno;
 8     private String dname;
 9     private String loc;
10     private Set<Emp> emps =new HashSet<Emp>();
11     
12     public Dept() {
13     }
14     
15     public Dept(Integer deptno, String dname, String loc) {
16         this.deptno = deptno;
17         this.dname = dname;
18         this.loc = loc;
19     }
20 
21     public Dept(Integer deptno, String dname, String loc, Set<Emp> emps) {
22         this.deptno = deptno;
23         this.dname = dname;
24         this.loc = loc;
25         this.emps = emps;
26     }
27     public Integer getDeptno() {
28         return deptno;
29     }
30     public void setDeptno(Integer deptno) {
31         this.deptno = deptno;
32     }
33     public String getDname() {
34         return dname;
35     }
36     public void setDname(String dname) {
37         this.dname = dname;
38     }
39     public String getLoc() {
40         return loc;
41     }
42     public void setLoc(String loc) {
43         this.loc = loc;
44     }
45     public Set<Emp> getEmps() {
46         return emps;
47     }
48     public void setEmps(Set<Emp> emps) {
49         this.emps = emps;
50     }
51 
52     @Override
53     public String toString() {
54         return "Dept [deptno=" + deptno + ", dname=" + dname + ", loc=" + loc + "]";
55     }
56     
57     
58 
59 }

Dept.java

5.在项目的src下的com.entity包下创建Emp.java

 1 package com.entity;
 2 
 3 
 4 
 5 public class Emp {
 6     private Integer empno;
 7     private String ename;
 8     private String job;
 9     private Integer sal;
10     private Dept dept;
11     
12     public Emp() {
13     }
14 
15     public Emp(Integer empno, String ename, String job, Integer sal) {
16         super();
17         this.empno = empno;
18         this.ename = ename;
19         this.job = job;
20         this.sal = sal;
21     }
22 
23     public Emp(Integer empno, String ename, String job, Integer sal, Dept dept) {
24         super();
25         this.empno = empno;
26         this.ename = ename;
27         this.job = job;
28         this.sal = sal;
29         this.dept = dept;
30     }
31 
32     public Integer getEmpno() {
33         return empno;
34     }
35 
36     public void setEmpno(Integer empno) {
37         this.empno = empno;
38     }
39 
40     public String getEname() {
41         return ename;
42     }
43 
44     public void setEname(String ename) {
45         this.ename = ename;
46     }
47 
48     public String getJob() {
49         return job;
50     }
51 
52     public void setJob(String job) {
53         this.job = job;
54     }
55 
56     public Integer getSal() {
57         return sal;
58     }
59 
60     public void setSal(Integer sal) {
61         this.sal = sal;
62     }
63 
64     public Dept getDept() {
65         return dept;
66     }
67 
68     public void setDept(Dept dept) {
69         this.dept = dept;
70     }
71 
72     @Override
73     public String toString() {
74         return "Emp [ empno=" + empno + ", ename=" + ename
75                 + ", job=" + job + ", sal=" + sal + "]";
76     }
77   
78 
79 
80 }

Emp.java

6.在项目的src下的com.entity包下创建Dept.hbm.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
 3 <hibernate-mapping>
 4    <class name="com.entity.Dept" table="DEPT">
 5      <id name="deptno" type="java.lang.Integer" column="DEPTNO">
 6        <generator class="assigned"/>
 7      </id>
 8      <property name="dname" type="java.lang.String" column="DNAME"/>
 9      <property name="loc" type="java.lang.String" column="LOC"/>
10      <!-- 一对多 -->
11      <set name="emps" inverse="true" cascade="save-update">
12         <key column="DEPTNO"></key>
13         <one-to-many class="com.entity.Emp"/>
14      </set>
15    </class>
16 </hibernate-mapping>

Dept.hbm.xml

7.在项目的src下的com.entity包下创建Emp.hbm.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
 3 <hibernate-mapping>
 4   <class name="com.entity.Emp" table="EMP">
 5      <id name="empno" type="java.lang.Integer" column="EMPNO">
 6        <generator class="assigned"/>
 7      </id>
 8      <property name="ename" type="java.lang.String" column="ENAME"/>
 9      <property name="job" type="java.lang.String" column="JOB"/>
10      <property name="sal" type="java.lang.Integer" column="SAL"/>
11      <!-- 多对一 -->
12      <many-to-one name="dept" class="com.entity.Dept" column="DEPTNO"/>
13   </class>
14 </hibernate-mapping>

Emp.hbm.xml

8.在项目的src下的com.dao包下创建DpetDao.java

  1 package com.dao;
  2 
  3 import java.util.List;
  4 
  5 import org.hibernate.Query;
  6 import org.hibernate.Session;
  7 
  8 import com.entity.Dept;
  9 import com.util.HibernateUtil;
 10 
 11 public class DpetDao {
 12 
 13     
 14     public static void main(String[] args) {
 15         System.out.println("-----------1.关联查询-----------");
 16         //getDept();
 17         System.out.println("-------2.内连接-------");
 18         innerJoin();
 19         System.out.println("-------3.迫切内连接-------");
 20         innerJoinFetch();
 21         System.out.println("-------4.左连接-------");
 22         leftJoin();
 23         System.out.println("-------5.迫切左连接-------");
 24         leftJoinFetch();
 25         System.out.println("-------6.右连接-------");
 26         rightJoin();
 27        
 28     }
 29     /**
 30      * 6.右连接
 31      */
 32     private static void rightJoin() {
 33         Session session=HibernateUtil.getSession();
 34         String hql="from Dept d right join d.emps ";
 35         Query query=session.createQuery(hql);
 36         /*list集合中的每个元素都是一个Object数组,数组的第一个元素时Dept对象,
 37          * 第二个元素时Emp对象,Dept对象的emps集合元素没有被初始化,
 38          * 即emps集合没有存放关联的Emp对象*/
 39         List<Object[]> list=query.list();
 40         System.out.println("dept对象"+"~~"+"emp对象");
 41         for (Object[] obj : list) {
 42             System.out.println(obj[0]);
 43             System.out.println(obj[1]);
 44         }
 45         HibernateUtil.closeSession();
 46         
 47     }
 48     /**
 49      * 5.迫切左连接
 50      */
 51     private static void leftJoinFetch() {
 52         Session session=HibernateUtil.getSession();
 53         /*Hibernate使用fetch关键字实现了将Emp对象读取出来后立即填充到对应的Dept对象
 54          * 的集合属性中,*/
 55         String hql="select distinct d from Dept d left join fetch d.emps ";
 56         Query query=session.createQuery(hql);
 57         List<Dept> list=query.list();
 58         for (Dept dept : list) {
 59             System.out.println(dept);
 60         }
 61         HibernateUtil.closeSession();
 62     }
 63     /**
 64      * 4.左连接
 65      */
 66     private static void leftJoin() {
 67         Session session=HibernateUtil.getSession();
 68         String hql="from Dept d left join d.emps ";
 69         Query query=session.createQuery(hql);
 70         /*list集合中的每个元素都是一个Object数组,数组的第一个元素时Dept对象,
 71          * 第二个元素时Emp对象,Dept对象的emps集合元素没有被初始化,
 72          * 即emps集合没有存放关联的Emp对象*/
 73         List<Object[]> list=query.list();
 74         System.out.println("dept对象"+"~~"+"emp对象");
 75         for (Object[] obj : list) {
 76             System.out.println(obj[0]);
 77             System.out.println(obj[1]);
 78         }
 79         HibernateUtil.closeSession();
 80     }
 81     /**
 82      * 3.迫切内连接
 83      */
 84     private static void innerJoinFetch() {
 85         Session session=HibernateUtil.getSession();
 86         /*Hibernate使用fetch关键字实现了将Emp对象读取出来后立即填充到对应的Dept对象
 87          * 的集合属性中,*/
 88         String hql="select distinct d from Dept d inner join fetch d.emps ";
 89         Query query=session.createQuery(hql);
 90         List<Dept> list=query.list();
 91         for (Dept dept : list) {
 92             System.out.println(dept);
 93         }
 94         HibernateUtil.closeSession();
 95     }
 96     /**
 97      * 2.内连接
 98      */
 99     private static void innerJoin() {
100         Session session=HibernateUtil.getSession();
101         String hql="from Dept d inner join d.emps ";
102         Query query=session.createQuery(hql);
103         /*list集合中的每个元素都是一个Object数组,数组的第一个元素时Dept对象,
104          * 第二个元素时Emp对象,Dept对象的emps集合元素没有被初始化,
105          * 即emps集合没有存放关联的Emp对象*/
106         List<Object[]> list=query.list();
107         System.out.println("dept对象"+"~~"+"emp对象");
108         for (Object[] obj : list) {
109             System.out.println(obj[0]);
110             System.out.println(obj[1]);
111         }
112         HibernateUtil.closeSession();
113     }
114     /**
115      * Exception in thread "main" java.lang.StackOverflowError
116      * 内存溢出:死循环
117      * hiberante双向关联时:打印内容时不能你中有我,我中有你,查询默认是懒加载
118      * 
119      */
120     private static void getDept() {
121         Session session=HibernateUtil.getSession();
122         String hql="from Dept";
123         Query query=session.createQuery(hql);
124         List<Dept> list=query.list();
125         for (Dept dept : list) {
126             System.out.println(dept);
127             System.out.println(dept.getEmps());
128         }
129         HibernateUtil.closeSession();
130         
131     }
132 
133 }

DpetDao.java

9.运行结果如下：remdeme.txt

 1 1.内连接
 2 Hibernate: 
 3     select
 4         dept0_.DEPTNO as DEPTNO0_0_,
 5         emps1_.EMPNO as EMPNO1_1_,
 6         dept0_.DNAME as DNAME0_0_,
 7         dept0_.LOC as LOC0_0_,
 8         emps1_.ENAME as ENAME1_1_,
 9         emps1_.JOB as JOB1_1_,
10         emps1_.SAL as SAL1_1_,
11         emps1_.DEPTNO as DEPTNO1_1_ 
12     from
13         DEPT dept0_ 
14     inner join
15         EMP emps1_ 
16             on dept0_.DEPTNO=emps1_.DEPTNO
17 2.迫切内连接
18  select
19         dept0_.DEPTNO as DEPTNO0_0_,
20         emps1_.EMPNO as EMPNO1_1_,
21         dept0_.DNAME as DNAME0_0_,
22         dept0_.LOC as LOC0_0_,
23         emps1_.ENAME as ENAME1_1_,
24         emps1_.JOB as JOB1_1_,
25         emps1_.SAL as SAL1_1_,
26         emps1_.DEPTNO as DEPTNO1_1_,
27         emps1_.DEPTNO as DEPTNO0__,
28         emps1_.EMPNO as EMPNO0__ 
29     from
30         DEPT dept0_ 
31     inner join
32         EMP emps1_ 
33             on dept0_.DEPTNO=emps1_.DEPTNO
34  -------4.左连接-------           
35 Hibernate: 
36     select
37         dept0_.DEPTNO as DEPTNO0_0_,
38         emps1_.EMPNO as EMPNO1_1_,
39         dept0_.DNAME as DNAME0_0_,
40         dept0_.LOC as LOC0_0_,
41         emps1_.ENAME as ENAME1_1_,
42         emps1_.JOB as JOB1_1_,
43         emps1_.SAL as SAL1_1_,
44         emps1_.DEPTNO as DEPTNO1_1_ 
45     from
46         DEPT dept0_ 
47     left outer join
48         EMP emps1_ 
49             on dept0_.DEPTNO=emps1_.DEPTNO  
50             
51  -------5.迫切左连接-------
52 Hibernate: 
53     select
54         distinct dept0_.DEPTNO as DEPTNO0_0_,
55         emps1_.EMPNO as EMPNO1_1_,
56         dept0_.DNAME as DNAME0_0_,
57         dept0_.LOC as LOC0_0_,
58         emps1_.ENAME as ENAME1_1_,
59         emps1_.JOB as JOB1_1_,
60         emps1_.SAL as SAL1_1_,
61         emps1_.DEPTNO as DEPTNO1_1_,
62         emps1_.DEPTNO as DEPTNO0__,
63         emps1_.EMPNO as EMPNO0__ 
64     from
65         DEPT dept0_ 
66     left outer join
67         EMP emps1_ 
68             on dept0_.DEPTNO=emps1_.DEPTNO
69  -------6.右连接-------
70 Hibernate: 
71     select
72         dept0_.DEPTNO as DEPTNO0_0_,
73         emps1_.EMPNO as EMPNO1_1_,
74         dept0_.DNAME as DNAME0_0_,
75         dept0_.LOC as LOC0_0_,
76         emps1_.ENAME as ENAME1_1_,
77         emps1_.JOB as JOB1_1_,
78         emps1_.SAL as SAL1_1_,
79         emps1_.DEPTNO as DEPTNO1_1_ 
80     from
81         DEPT dept0_ 
82     right outer join
83         EMP emps1_ 
84             on dept0_.DEPTNO=emps1_.DEPTNO

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原文地址：https://www.cnblogs.com/holly8/p/5778112.html