Hibernate多对多双向关联的配置

2020年8月7日 08:26:06Linux大全评论427 views阅读模式

Hibernate的双向多对多关联有两种配置方法:那我们就来看看两种方案是如何配置的。

一、创建以各自类为类型的集合来关联

1.首先我们要在两个实体类(雇员<Emploee>、工程<Project>)中各自给对方添加一个对方的集合

1.1 雇员实体类

package cn.manytomany.one;

import java.util.HashSet;
import java.util.Set;

public class Emploee {
//雇员id
private Integer empId;
//工程
private String empName;
//工程的集合
private Set<Project> projects=new HashSet<Project>();

public Set<Project> getProjects() {
return projects;
}
public void setProjects(Set<Project> projects) {
this.projects = projects;
}
public Integer getEmpId() {
return empId;
}
public void setEmpId(Integer empId) {
this.empId = empId;
}
public String getEmpName() {
return empName;
}
public void setEmpName(String empName) {
this.empName = empName;
}
}

1.2 工程实体类

package cn.manytomany.one;

import java.util.HashSet;
import java.util.Set;

public class Project {
private Integer proId;
private String proName;
private Set<Emploee> emploees=new HashSet<Emploee>();

public Set<Emploee> getEmploees() {
return emploees;
}
public void setEmploees(Set<Emploee> emploees) {
this.emploees = emploees;
}
public Integer getProId() {
return proId;
}
public void setProId(Integer proId) {
this.proId = proId;
}
public String getProName() {
return proName;
}
public void setProName(String proName) {
this.proName = proName;
}

}

2.有了实体类之后呢,我们就能通过实体的属性和数据库的表字段配置映射关系。

2.1 emploees.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.manytomany.one">
<class name="Emploee" table="Emploee">
<id name="empId">
<generator class="sequence">
<param name="sequence">SQU_NUM</param>
</generator>
</id>
<property name="empName"></property>
<set name="projects" table="PROEMP">
<key column="RPROID"></key>
<many-to-many class="Project" column="REMPID">
</many-to-many>
</set>
</class>
</hibernate-mapping>

2.2 projects.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.manytomany.one">
<class name="Project" table="PROJECT">
<id name="proId">
<generator class="sequence">
<param name="sequence">SQU_NUM</param>
</generator>
</id>
<property name="proName"></property>

<set name="emploees" table="PROEMP" cascade="save-update">
<key column="REMPID"></key>
<many-to-many class="Emploee" column="RPROID">
</many-to-many>
</set>
</class>
</hibernate-mapping>

2.3 另外还有一个最重要的大配置来引用两个小配置

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<property name="connection.driver_class">
Oracle.jdbc.OracleDriver
</property>
<property name="connection.url">
jdbc:oracle:thin:@localhost:1521:orcl
</property>
<property name="connection.username">happy</property>
<property name="connection.password">1</property>

<property name="dialect">
org.hibernate.dialect.Oracle10gDialect
</property>

<property name="show_sql">true</property>

<property name="format_sql">true</property>

<property name="hbm2ddl.auto">create</property>

<mapping resource="cn/manytomany/doubleanother/emploees.hbm.xml" />
<mapping resource="cn/manytomany/doubleanother/projects.hbm.xml" />

</session-factory>
</hibernate-configuration>

3.最后就是测试类了

package cn.manytomany.one;

import org.hibernate.Session;
import org.hibernate.Transaction;

public class ManyToManyDoubleTest {

/**
* 多对多的双向关联测试
*/
public static void main(String[] args) {
Session session = HibernateUtil.currentSession();
Transaction tsc = session.beginTransaction();
//创建雇员
Emploee emp=new Emploee();
emp.setEmpName("田超");
Emploee emp1=new Emploee();
emp1.setEmpName("施强");

//创建工程
Project pro=new Project();
pro.setProName("开发工程");
pro.getEmploees().add(emp);
pro.getEmploees().add(emp1);
try {
session.save(pro);
tsc.commit();
} catch (Exception e) {
// 回滚
tsc.rollback();
}
HibernateUtil.closeSession();
}

}

3.1 最后补充一下工具类,看看就行

package cn.manytomany.one;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.Session;
/*
* session工具类
*/
public class HibernateUtil {

private static final ThreadLocal<Session> sessionTL=new ThreadLocal<Session>();
private static Configuration cfg;
private static final SessionFactory sf;
static{
try {
cfg=new Configuration().configure();
sf = cfg.buildSessionFactory();
} catch (Exception e) {
//异常
e.printStackTrace();
throw new ExceptionInInitializerError(e);
}
}
public static Session currentSession(){
Session session=sessionTL.get();
//如果session为null,则打开一个新的session
if (session==null) {
session=sf.openSession();
sessionTL.set(session);
}
return session;
}
public static void closeSession(){
Session session=sessionTL.get();
sessionTL.set(null);
session.close();

}

}

二、创建一个中间的实体类来关联

1.跟第一个方案差不多,先实现三个实体类,代码如下:

package cn.manytomany.doubleanother;

import java.util.HashSet;
import java.util.Set;

public class Emploee {

private Integer empId;
private String empName;
private Set<ProEmp> proemp=new HashSet<ProEmp>(); //集合的类型为中间的实体类类型
public Set<ProEmp> getProemp() {
return proemp;
}
public void setProemp(Set<ProEmp> proemp) {
this.proemp = proemp;
}
public Integer getEmpId() {
return empId;
}
public void setEmpId(Integer empId) {
this.empId = empId;
}
public String getEmpName() {
return empName;
}
public void setEmpName(String empName) {
this.empName = empName;
}

}

package cn.manytomany.doubleanother;

import java.util.HashSet;
import java.util.Set;

public class Project {
private Integer proId;
private String proName;

//集合的类型依然为中间的实体类类型
private Set<ProEmp> proemp=new HashSet<ProEmp>();

public Set<ProEmp> getProemp() {
return proemp;
}
public void setProemp(Set<ProEmp> proemp) {
this.proemp = proemp;
}
public Integer getProId() {
return proId;
}
public void setProId(Integer proId) {
this.proId = proId;
}
public String getProName() {
return proName;
}
public void setProName(String proName) {
this.proName = proName;
}

}

1.1 补充的中间实体类

package cn.manytomany.doubleanother;

public class ProEmp {

private Integer id;
private Emploee emp;
private Project pro;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Emploee getEmp() {
return emp;
}
public void setEmp(Emploee emp) {
this.emp = emp;
}
public Project getPro() {
return pro;
}
public void setPro(Project pro) {
this.pro = pro;
}

}

2. 接下来就是小配置了,跟第一个方案格式几乎是一样的,就不过多解释了,直接来看小配置就行了。

因为我们要用中间实体类来关联，所以雇员类（Emploee）和工程类(Project)没有什么眼添加的,只需按照正常的配置即可。

2.1 emploees.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.manytomany.doubleanother">
<class name="Emploee" table="Emploee">
<id name="empId">
<generator class="sequence">
<param name="sequence">SQU_NUM</param>
</generator>
</id>
<property name="empName"></property>
</class>
</hibernate-mapping>

2.2 emploees.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.manytomany.doubleanother">
<class name="Project" table="PROJECT">
<id name="proId">
<generator class="sequence">
<param name="sequence">SQU_NUM</param>
</generator>
</id>
<property name="proName"></property>
</class>
</hibernate-mapping>

2.3 关键就在于 proemp.hbm.xml (把多对多关联转化成两个多对一来关联)

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.manytomany.doubleanother">
<class name="ProEmp" table="PROEMPNEW">
<id name="id">
<generator class="sequence">
<param name="sequence">SQU_NUM</param>
</generator>
</id>
<many-to-one name="emp" class="Emploee" column="EMPID">
</many-to-one>
<many-to-one name="pro" class="Project" column="PROID">
</many-to-one>
</class>
</hibernate-mapping>

3. 现在就可以进行测试类测试数据了

package cn.manytomany.doubleanother;

import org.hibernate.Session;
import org.hibernate.Transaction;

import cn.manytomany.one.HibernateUtil;

public class ManyToManyDoubleOnlyAnother {

/**
* 多对多双向关联---两个多对一关联
*/
public static void main(String[] args) {
Session session = HibernateUtil.currentSession();
Transaction tsc = session.beginTransaction();
//创建雇员
Emploee emp=new Emploee();
emp.setEmpName("田超");

//创建工程
Project pro=new Project();
pro.setProName("开发工程");

//中间类
ProEmp proemp=new ProEmp();
proemp.setEmp(emp);
proemp.setPro(pro);
try {
//保存
session.save(emp);
session.save(pro);
session.save(proemp);
tsc.commit();
} catch (Exception e) {
// 回滚
tsc.rollback();
}
HibernateUtil.closeSession();