hibernate多對多 關聯映射(many-to-many)
在操作和性能方面都不太理想，所以多對多的映射使用較少，實際使用中最好轉換成一對多的對象模型；
hibernate會為我們創建中間關聯表，轉換成兩個一對多。
（1）一個最簡單的例子就是學生選課的數據表了
（2）student.java
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public class course { private integer id; private string name; private set<stucourse> stucourses; //get/set方法} |
（3）student.java
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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學生選課表
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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
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<?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 表示一門課程可以對應多個選課記錄 --> <set name="stucourses"> <key column="course_id" /> <one-to-many class="stucourse" /> </set> </class></hibernate-mapping> |
（6）student.hbm.xml文件
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<?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> <!-- 這里我們配置了one-to-many 一個學生可以對應多個選課記錄 --> <set name="stucourses"> <key column="student_id" /> <!-- 這里的column是外鍵 --> <one-to-many class="stucourse" /> <!-- many所對應的表 --> </set> </class></hibernate-mapping> |
（7）stucourse.hbm.xml文件
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<?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
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<?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> <!-- 配置讓hibernate自動創建關系模型(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> |
總結
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原文鏈接：https://blog.csdn.net/huanglong1218/article/details/52313047
