Hibernate实现many-to-many的映射关系

Hibernate多对多 关联映射(many-to-many)

在操作和性能方面都不太理想，所以多对多的映射使用较少，实际使用中最好转换成一对多的对象模型；

Hibernate会为我们创建中间关联表，转换成两个一对多。

（1）一个最简单的例子就是学生选课的数据表了

（2）Student.java

public class Course {
 private Integer id;
 private String name;
 private Set<StuCourse> stuCourses;
 //get/set方法
}

（3）Student.java

public class Student {
 private Integer id;
 private String name;
 private Set<StuCourse> stuCourses;
 <span style="font-family: Arial, Helvetica, sans-serif;">//get/set方法</span>
}

（4）StuCourse.java学生选课表

package com.hsp.domain;
public class StuCourse {
 private Integer id;
 private Student student;
 private Course course;
 private Integer grade;
 //get/set方法
}

（5）Course.hbm.xml文件

<?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="com.hsp.domain">
 <class name="Course">
 <id name="id" type="java.lang.Integer">
  <generator class="sequence">
  <param name="sequence">course_seq</param>
  </generator>
 </id>
 <property name="name" type="java.lang.String">
  <column name="name" length="64" />
 </property>
 <!-- 配置one-to-many 表示一门课程可以对应多个选课记录 -->
 <set name="stuCourses">
  <key column="course_id" />
  <one-to-many class="StuCourse" />
 </set>
 </class>
</hibernate-mapping>

（6）Student.hbm.xml文件

<?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="com.hsp.domain">
 <class name="Student">
 <id name="id" type="java.lang.Integer">
  <generator class="sequence">
  <param name="sequence">stu_seq</param>
  </generator>
 </id>
 <property name="name" type="java.lang.String">
  <column name="name" length="64" />
 </property>
  <!-- 这里我们配置了one-to-many 一个学生可以对应多个选课记录 -->
 <set name="stuCourses">
  <key column="student_id" /> <!-- 这里的column是外键 -->
  <one-to-many class="StuCourse" /> <!-- many所对应的表 -->
 </set>
 </class>
</hibernate-mapping>

（7）StuCourse.hbm.xml文件

<?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="com.hsp.domain">
 <class name="StuCourse">
 <id name="id" type="java.lang.Integer">
  <generator class="sequence">
  <param name="sequence">stucourse_seq</param>
  </generator>
 </id>
 <property name="grade" type="java.lang.Integer">
  <column name="grade" length="3" />
 </property>
 <many-to-one name="course" column="course_id" />
 <many-to-one name="student" column="student_id" />
 </class>
</hibernate-mapping>

（8）hibernate.cfg.xml文件

<?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">
<!-- Generated by MyEclipse Hibernate Tools. -->
<hibernate-configuration>
 <session-factory>
 <property name="connection.username">root</property>
 <property name="connection.url">
  jdbc:oracle:thin:@127.0.0.1:1521:OracleDB
 </property>
 <property name="dialect">
  org.hibernate.dialect.Oracle9Dialect
 </property>
 <property name="connection.password">root</property>
 <property name="connection.driver_class">
  oracle.jdbc.driver.OracleDriver
 </property>
 <property name="show_sql">true</property>
 <!-- 配置让hibernate自动创建关系模型(表) -->
 <property name="hbm2ddl.auto">update</property>
 <mapping resource="com/hsp/domain/Course.hbm.xml" />
 <mapping resource="com/hsp/domain/StuCourse.hbm.xml" />
 <mapping resource="com/hsp/domain/Student.hbm.xml" />
 </session-factory>
</hibernate-configuration>

总结

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