hibernate双向多对多关联-优快云博客

本文链接：https://blog.youkuaiyun.com/CSC_Cockroach/article/details/52986208

一.

注意：1.在持久化类里面写set的时候一定要初始化，否则会出现初始化问题

2.在类关联文件中要设置

二.代码

1.AItem类

package cn.edu.sdut.hibernate.nton;

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

public class AItem {

	private int aId;
	private String aName;
	
	<span style="color:#ff0000;">private Set<BItem> bSet = new HashSet<>();//注意为set初始化，否则会出现空指针异常</span>

	public int getaId() {
		return aId;
	}

	public void setaId(int aId) {
		this.aId = aId;
	}

	public String getaName() {
		return aName;
	}

	public void setaName(String aName) {
		this.aName = aName;
	}

	public Set<BItem> getbSet() {
		return bSet;
	}

	public void setbSet(Set<BItem> bSet) {
		this.bSet = bSet;
	}


	
}

2.BItem类

package cn.edu.sdut.hibernate.nton;

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


public class BItem {

	private int bId;
	private String bName;
	<span style="color:#ff0000;">private Set<AItem> aSet = new HashSet<>();//注意为set初始化，否则会出现空指针异常</span>
	
	public Set<AItem> getaSet() {
		return aSet;
	}
	public void setaSet(Set<AItem> aSet) {
		this.aSet = aSet;
	}
	public int getbId() {
		return bId;
	}
	public void setbId(int bId) {
		this.bId = bId;
	}
	public String getbName() {
		return bName;
	}
	public void setbName(String bName) {
		this.bName = bName;
	}
	
	
}

3.AItem.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2016-10-30 23:47:20 by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
    <class name="cn.edu.sdut.hibernate.nton.AItem" table="AITEM">
        <id name="aId" type="int">
            <column name="A_ID" />
            <generator class="native" />
        </id>
        <property name="aName" type="java.lang.String" >
            <column name="A_NAME" />
        </property>
        
       <span style="color:#ff0000;"> <!-- table: 指定中间表 -->
        <set name="bSet" table="AITEM_BITEM"><!-- inverse="true" 双向的时候一边加上就行，否则出现主键冲突-->
            <key>
            	<!-- 设置当前表在中间表的外键 -->
                <column name="AID" />
            </key>
            <!-- 使用 many-to-many 指定多对多的关联关系. column 执行 bSet 集合中的持久化类在中间表的外键列的名称,也就是另一张表在中间表的外键  -->
            <many-to-many class="cn.edu.sdut.hibernate.nton.BItem" column="BID"/>
        </set></span>
    </class>
</hibernate-mapping>

4.BItem.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2016-10-30 23:47:20 by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
    <class name="cn.edu.sdut.hibernate.nton.BItem" table="BITEM">
        <id name="bId" type="int" >
            <column name="B_ID" />
            <generator class="native" />
        </id>
        <property name="bName" type="java.lang.String" >
            <column name="B_NAME" />
        </property>
        <!-- -->
        <span style="color:#ff0000;"> <set name="aSet" table="AITEM_BITEM" inverse="true"><!-- inverse="true" 双向的时候一边加上就行，否则出现主键冲突-->
            <key>
            	<!-- 设置当前表在中间表的外键 -->
                <column name="BID" />
            </key>
            <!-- 使用 many-to-many 指定多对多的关联关系. column 执行 bSet 集合中的持久化类在中间表的外键列的名称,也就是另一张表在中间表的外键  -->
            <many-to-many class="cn.edu.sdut.hibernate.nton.AItem" column="AID"/>
        </set></span>
         
    </class>
</hibernate-mapping>

5.hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
		"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
		"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
    	
    	<!-- 配置连接数据库的基本信息 -->
    	<property name="connection.username">root</property>
    	<property name="connection.password">csc</property>
    	<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
    	<property name="connection.url">jdbc:mysql:///hibernate5</property>
    
    	<!-- 配置hibernate的基本信息 -->
    	<!-- hibernate 所使用的数据库方言 -->
    	<property name="dialect">org.hibernate.dialect.MySQLInnoDBDialect</property>
    	
    	<!-- 执行sql时是否在控制台上打印 -->
    	<property name="show_sql">true</property>
    	
    	<!-- 是否对sql进行格式化 -->
    	<property name="format_sql">true</property>
    	
    	<!-- 指定自动生成数据表的策略 -->
    	<property name="hbm2ddl.auto">update</property>
    	
    	<!-- 指定session的delete方法会把对象的id置为null -->
    	<property name="hibernate.use_identifier_rollback">true</property>
    	
    	<!-- 指定数据库的隔离级别 -->
    	<property name="connection.isolation">2</property>
    	
    	<!-- 配置c3p0数据池 -->
    	<property name="hibernate.c3p0.max_size">100</property>
    	<property name="hibernate.c3p0.min_size">20</property>
    	<property name="hibernate.c3p0.acquire_increment">5</property>
    	<property name="hibernate.c3p0.timeout">2000</property>
    	<property name="hibernate.c3p0.idle_test_period">2000</property>
    	<property name="hibernate.c3p0.max_statements">10</property>
    	
    	<!-- 设定JDBC的statment读取数据的时候每次在数据库中读取的记录的条数 -->
    	<property name="hibernate.jdbc.fetch_size">100</property>
    	<!-- 设定对数据进行批量操作，批次更新和批次插入的批次大小 -->
    	<property name="hibernate.jdbc.batch_size">30</property>
    	
    	<!-- 指定关联的xxx.hbm.xml文件 -->
    	<mapping resource="cn/edu/sdut/hibernate/helloworld/News.hbm.xml"/>
    	<mapping resource="cn/edu/sdut/hibernate/manytoone/Customer.hbm.xml"/>
    	<mapping resource="cn/edu/sdut/hibernate/manytoone/Order.hbm.xml"/>
    	<!--  
    	<mapping resource="cn/edu/sdut/hibernate/onetoone/Department.hbm.xml"/>
    	<mapping resource="cn/edu/sdut/hibernate/onetoone/Manager.hbm.xml"/>
    	
    	<mapping resource="cn/edu/sdut/hibernate/onetoone2/Department.hbm.xml"/>
    	<mapping resource="cn/edu/sdut/hibernate/onetoone2/Manager.hbm.xml"/>
    	-->
    	<mapping resource="cn/edu/sdut/hibernate/nton/AItem.hbm.xml"/>
    	<mapping resource="cn/edu/sdut/hibernate/nton/BItem.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

6.TestNtoN类

package cn.edu.sdut.hibernate.nton;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

public class TestNtoN {

	private SessionFactory sessionFactory;
	private Session session;
	private Transaction transaction;
	
	@Before
	public void init(){
		Configuration configuration = new Configuration().configure();
		ServiceRegistry serviceRegistry = 
				new ServiceRegistryBuilder().applySettings(configuration.getProperties())
											.buildServiceRegistry();
		sessionFactory = configuration.buildSessionFactory(serviceRegistry);
		session = sessionFactory.openSession();
		transaction = session.beginTransaction();
	}
	@After
	public void destory(){
		transaction.commit();
		session.close();
		sessionFactory.close();
	}
	
	
	@Test
	public void testSave(){
		AItem aItem = new AItem();
		aItem.setaName("AA1");
		AItem aItem2 = new AItem();
		aItem2.setaName("AA2");
		BItem bItem = new BItem();
		bItem.setbName("BB1");
		BItem bItem2 = new BItem();
		bItem2.setbName("BB2");
		
		aItem.getbSet().add(bItem);
		aItem.getbSet().add(bItem2);
		aItem2.getbSet().add(bItem);
		aItem2.getbSet().add(bItem2);
		
		bItem.getaSet().add(aItem);
		bItem.getaSet().add(aItem2);
		bItem2.getaSet().add(aItem);
		bItem2.getaSet().add(aItem2);
		
		session.save(aItem);
		session.save(aItem2);
		session.save(bItem);
		session.save(bItem2);
	}
	
	@Test
	public void testGet(){
		AItem aItem = (AItem) session.get(AItem.class, 1);
		System.out.println(aItem.getbSet());
		BItem bItem = (BItem) session.get(BItem.class, 1);
		System.out.println(bItem.getaSet().getClass().getName());
	}
}