今天小编就为大家分享一篇关于Hibernate实现many-to-many的映射关系,小编觉得内容挺不错的,现在分享给大家,具有很好的参考价值,需要的朋友一起跟随小编来看看吧
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.javapublic class course {
private integer id;
private string name;
private set<stucourse> stucourses;
//get/set方法
} (3)student.javapublic class student {
private integer id;
private string name;
private set<stucourse> stucourses;
<span>//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
以上就是这篇文章的全部内容了,希望本文的内容对大家的学习或者工作具有一定的参考学习价值,谢谢大家对CodeAE代码之家的支持。如果你想了解更多相关内容请查看下面相关链接
原文链接:https://blog.csdn.net/huanglong1218/article/details/52313047
|