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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