20150708 MyEclipse Hibernate Many To Many Mapping

Many-To-Many 例子：

创建三张表: 

Person: 

uid	uname
1	Jason

Project:

pid	pro_name
1	java

Pro_per: 关联person 和 project，表示参与了项目的人。uid 和 pid 为联合主键

pid	uid
1	1

ManyToMany：一个人可以参加多个项目，一个项目也可以有多个人参加。

OneToMany的时候用 reverse engineering 可以生成关联的内部数据类型 Set， 但ManyToMany不会生成Set，所以要自己在类里面手写 Set，而且要在hbm.xml 里面自己手写Set 的标签。

Person.java:

package entity;

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

/**
 * Person entity. @author MyEclipse Persistence Tools
 */

public class Person implements java.io.Serializable {

	// Fields

	private Integer uid;
	private String uname;
	private Set projects = new HashSet();

	// Constructors

	/** default constructor */
	public Person() {
	}

	/** full constructor */
	public Person(String uname) {
		this.uname = uname;
	}

	// Property accessors

	public Integer getUid() {
		return this.uid;
	}

	public void setUid(Integer uid) {
		this.uid = uid;
	}

	public String getUname() {
		return this.uname;
	}

	public void setUname(String uname) {
		this.uname = uname;
	}

	public Set getProjects() {
		return projects;
	}

	public void setProjects(Set projects) {
		this.projects = projects;
	}

	
	
}

Project.java:

package entity;

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

/**
 * Project entity. @author MyEclipse Persistence Tools
 */

public class Project implements java.io.Serializable {

	// Fields

	private Integer pid;
	private String proName;
	private Set Persons = new HashSet();

	// Constructors

	/** default constructor */
	public Project() {
	}

	/** full constructor */
	public Project(String proName) {
		this.proName = proName;
	}

	// Property accessors

	public Integer getPid() {
		return this.pid;
	}

	public void setPid(Integer pid) {
		this.pid = pid;
	}

	public String getProName() {
		return this.proName;
	}

	public void setProName(String proName) {
		this.proName = proName;
	}

	public Set getPersons() {
		return Persons;
	}

	public void setPersons(Set persons) {
		Persons = persons;
	}

}

Person.hbm.xml: 

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="entity.Person" table="person" catalog="hibernate_1">
        <id name="uid" type="java.lang.Integer">
            <column name="uid" />
            <generator class="native"></generator>
        </id>
        <property name="uname" type="java.lang.String">
            <column name="uname" />
        </property>
               
        <strong><em><span style="color:#ff0000;"><set name = "projects" table = "pro_per">
        	<key column = "uid">
        	</key>        	     
        	<many-to-many class = "entity.Project"	column = "pid">
        	</many-to-many>
        </set></span></em></strong>
        
    </class>
</hibernate-mapping>

Project.hbm.xml:

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="entity.Project" table="project" catalog="hibernate_1">
        <id name="pid" type="java.lang.Integer">
            <column name="pid" />
            <generator class="native"></generator>
        </id>
        <property name="proName" type="java.lang.String">
            <column name="pro_name" />
        </property>
         
       <span style="color:#ff0000;"> <strong><set name = "persons" table = "pro_per">
        	<key column = "pid">
        	</key>        	     
        	<many-to-many class = "entity.Person"	column = "uid">
        	</many-to-many>
        </set></strong></span>
        
    </class>
</hibernate-mapping>

Test 1: 新建Person("Jason"), 从数据库读出pid=1 的project， 在person的Set 中加入该project，保存person的时候，关联关系也会自动保存到第三张表(Proj_per)里面。

package test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import sessionfactory.HibernateSessionFactory;
import entity.Person;
import entity.Project;

public class Test {
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Session s = HibernateSessionFactory.getSession();		
			Project pro = (Project) s.load(Project.class, 1);
			Person per = new Person("Jason");		
			per.getProjects().add(pro);		
			Transaction t = s.beginTransaction();			
				s.save(per);				
			t.commit();
		s.close();		
	}
}

生成的sql 语句：

Hibernate: insert into hibernate_1.person (uname) values (?)
Hibernate: insert into pro_per (uid, pid) values (?, ?)

在Person 和 Pro_per 两个表内都做添加。

Person (增加1-Jason):

uid	uname
1	Jason

Project ( 无变化):

pid	pro_name
1	java

Pro_per (增加1-1):

pid	uid
1	1

同理，也可以load出一个person，添加到新建的一个project的set里，结果在Project 和 Pro_per 两个表里都做添加：

package test;

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

import sessionfactory.HibernateSessionFactory;
import entity.Person;
import entity.Project;

public class Test2 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Session s = HibernateSessionFactory.getSession();		
			Person per = (Person)s.load(Person.class, 4);
			Project pro = new Project("iOS");
			pro.getPersons().add(per);		
			Transaction t = s.beginTransaction();		
				s.save(pro);		
			t.commit();
		s.close();
	}
}

Calvin 为 uid = 4 的person 的uname

Person (无变化):

uid	uname
...	...
4	Calvin

Project (增加2-iOS):

pid	pro_name
1	java
2	iOS

Pro_per (增加2-4):

pid	uid
1	1
2	4