Hibernate从入门到精通（6）- 双向 多对多

使用学生-教师进行测试：

如下图：

在Hibernate多对多关系中，数据库存数据多添加一张关系表，用来维持两个实体之间的关系。

XML配置文件

1.添加需要使用的jar文件

1.1数据库驱动包 ojdbc.jar

1.2Hibernate文件中的lib文件夹中的所有jar文件

2.创建hibernate.cfg.xml文件（*注意不要写Session factory name）

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>        <property name="hibernate.connection.driver_class">        oracle.jdbc.driver.OracleDriver</property>        <property name="hibernate.connection.password">        xukai</property>        <property name="hibernate.connection.url">        jdbc:oracle:thin:@10.25.112.21:1521:orcl</property>        <property name="hibernate.connection.username">        xukai</property>        <property name="hibernate.dialect">        org.hibernate.dialect.Oracle10gDialect</property>        <!-- 创建表 -->    <property name="hibernate.hbm2ddl.auto">update</property>    <!-- 控制台输出SQL语句 -->    <property name="show_sql">true</property>    <!-- 输出语句格式化 -->    <property name="format_sql">true</property>        </session-factory></hibernate-configuration>

3.创建实体类，实现Serializable接口

package com.edu.entity;import java.io.Serializable;import java.util.HashSet;import java.util.Set;/** * @author xukai * 2015年11月22日下午8:29:15 */public class StudentInfo implements Serializable {private static final long serialVersionUID = 1L;private Integer stuId;private String stuName;private String sex;private Set<TeacherInfo> teas = new HashSet<>();//getter setter}

package com.edu.entity;import java.io.Serializable;import java.util.HashSet;import java.util.Set;/** * @author xukai * 2015年11月22日下午8:29:45 */public class TeacherInfo implements Serializable {private static final long serialVersionUID = 1L;private Integer teaId;private String teaName;private String sex;private Set<StudentInfo> stus = new HashSet<>();<span style="white-space:pre"></span>//getter setter}

4.创建hibernate mapping xml file

StudentInfo.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 2015-11-22 20:33:48 by Hibernate Tools 3.4.0.CR1 --><hibernate-mapping>    <class name="com.edu.entity.StudentInfo" table="STUDENTINFO_TEST3">        <id name="stuId" type="java.lang.Integer">            <column name="STU_ID" />            <generator class="assigned" />        </id>        <property name="stuName" type="java.lang.String">            <column name="STU_NAME" />        </property>        <property name="sex" type="java.lang.String">            <column name="SEX" />        </property>        <set name="teas" table="S_T_R_TEST3" inverse="true" lazy="true">            <key>                <column name="R_STU_ID" />            </key>            <many-to-many class="com.edu.entity.TeacherInfo"             column="R_TEA_ID"/> <!-- 这里注意column一定要添加，还有实体类 -->        </set>    </class></hibernate-mapping>

TeacherInfo.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 2015-11-22 20:33:48 by Hibernate Tools 3.4.0.CR1 --><hibernate-mapping>    <class name="com.edu.entity.TeacherInfo" table="TEACHERINFO_TEST3">        <id name="teaId" type="java.lang.Integer">            <column name="TEA_ID" />            <generator class="assigned" />        </id>        <property name="teaName" type="java.lang.String">            <column name="TEA_NAME" />        </property>        <property name="sex" type="java.lang.String">            <column name="SEX" />        </property>        <set name="stus" table="S_T_R_TEST3" inverse="false" lazy="true">            <key>                <column name="R_TEA_ID" />            </key>            <!-- 这里注意column一定要添加 -->            <many-to-many class="com.edu.entity.StudentInfo"             column="R_STU_ID"/>        </set>    </class></hibernate-mapping>

(*注:我测试的时候忘记添加column了，一样测试通过了，但是数据库关系表中多了一条字段，elt

 create table S_T_R_TEST3 (        S_STU_ID number(10,0) not null,        elt number(10,0) not null,        R_TEA_ID number(10,0) not null,        primary key (R_TEA_ID, elt)    )

)

5.在hibernate.cfg.xml中添加映射关系

<span style="white-space:pre"></span><!-- 关联映射文件 -->    <mapping resource="com/edu/entity/StudentInfo.hbm.xml"/>    <mapping resource="com/edu/entity/TeacherInfo.hbm.xml"/>

6.使用JUnit测试：

package config;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.boot.registry.StandardServiceRegistryBuilder;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;import org.junit.After;import org.junit.Before;import org.junit.Ignore;import org.junit.Test;import com.edu.entity.StudentInfo;import com.edu.entity.TeacherInfo;/** * @author xukai 2015年11月22日下午8:44:57 */public class TestConfig {private static SessionFactory factory;private static Session session;/** * 读取配置文件信息 */static {Configuration config = new Configuration().configure();ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(config.getProperties()).build();factory = config.buildSessionFactory(serviceRegistry);}@Beforepublic void init(){session = factory.openSession();}@Ignore@Testpublic void testConfig(){}/** * 进行事务操作 */@Test public void testSave(){//保存教师和学生//开启事务Transaction transaction = session.beginTransaction();StudentInfo student = new StudentInfo();student.setStuId(9);student.setStuName("学生1");student.setSex("男");TeacherInfo teacher = new TeacherInfo();teacher.setTeaId(10);teacher.setTeaName("教师2");teacher.setSex("女");/** * 以下两句至少有一句 *///student.getTeas().add(teacher);teacher.getStus().add(student);session.save(teacher);session.save(student);transaction.commit();//提交事务}/** * 查询 */@Ignore@Testpublic void testGet(){StudentInfo student = (StudentInfo) session.get(StudentInfo.class, 1);System.out.println(student);}@Afterpublic void after(){//关闭if(session != null && session.isOpen()){session.close();}}}

注解（Annotation）

实体类：StudentInfo：

package com.edu.entity;import java.io.Serializable;import java.util.HashSet;import java.util.Set;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.Id;import javax.persistence.ManyToMany;import javax.persistence.Table;/** * @author xukai * 2015年11月23日下午8:55:19 */@Entity@Table(name="STUDENT_INFO_TEST4")public class StudentInfo implements Serializable {private static final long serialVersionUID = 1L;@Id@Column(name="stu_id")private Integer stuId;@Column(name="stu_name")private String stuName;@Column(name="sex")private String sex;//关系由对方维护@ManyToMany(targetEntity=TeacherInfo.class,mappedBy="stus")private Set<TeacherInfo> teas = new HashSet<>();<span style="white-space:pre"></span>//getter setter}

TeacherInfo:

package com.edu.entity;import java.io.Serializable;import java.util.HashSet;import java.util.Set;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToMany;import javax.persistence.Table;/** * @author xukai * 2015年11月23日下午8:54:29 */@Entity()@Table(name="TEACHER_INFO_TEST4")public class TeacherInfo implements Serializable {private static final long serialVersionUID = 1L;@Id@Column(name="tea_id")private Integer teaId;@Column(name="tea_name")private String teaName;@Column(name="sex")private String sex;@ManyToMany(targetEntity=StudentInfo.class)@JoinTable(name="R_S_T_TEST4",joinColumns={@JoinColumn(name="R_TEA_ID")},inverseJoinColumns={@JoinColumn(name="R_STU_ID")})private Set<StudentInfo> stus = new HashSet<>();}

hibernate.cfg.xml中关系映射改为：

<span style="white-space:pre"></span><mapping class="com.edu.entity.StudentInfo"/>    <mapping class="com.edu.entity.TeacherInfo"/>

上面的那个测试类，依然可以通过。下面为测试截图：

exception：

  org.hibernate.AnnotationException: No identifier specified for entity.

  在对Entity进行对象关系映射的时候忘记加上主键@Id了。这个错是hibernate的  annotation报的错，所以肯定是对象上加的注解有问题。