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example：
老师(teacher)和学生(Student)就是一个多对多的关系吧？老师可以有多个学生，学生也可以由多个老师，那在Hibernate中多对多是怎样实现的呢？？
在Hibernate中多对多关系分为两种：1单向的多对多，2双向的多对多
下面详细说明一些两种有什么不同和实现步骤
I单向的多对多实现步骤：
1新建teacher、student表，可以任意选择在其中一个表添加另一个表的集合，（例如在teacher中添加student的set<Student>集合，例如private set<student> students）
代码如下：
teacher：
package com.atguigu.hibernate.n2n; import java.util.Set; public class Teacher { private Integer ID; private String Name; private Set<Student> students; public Integer getID() { return ID; } public void setID(Integer iD) { ID = iD; } public String getTea_Name() { return Name; } public void setTea_Name(String Name) { this.Name =Name; } public Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } }
Student：
package com.atguigu.hibernate.n2n; public class Student { private Integer S_ID; private String s_Name; public Integer getS_ID() { return S_ID; } public void setS_ID(Integer s_ID) { S_ID = s_ID; } public String getS_Name() { return s_Name; } public void setS_Name(String s_Name) { this.s_Name = s_Name; } }
2在有set集合属性的持久化类的.hbm.xml文件里添加集合信息和many-to-many信息，另外一个表的.hbm.xml文件跟平常一样即可
teacher：
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.atguigu.hibernate.n2n.Teacher" table="TEACHER"> <id name="ID" type="java.lang.Integer"> <column name="ID" /> <generator class="native" /> </id> <property name="Name" type="java.lang.String" access="field"> <column name="NAME" /> </property> <!-- name:set集合的名字 Table：中间表的名字 key--column:中间表的外键列的名字，这个类的值就是属于<class name="">这个类的ID值 many-to-many的column：也是指定中间表的外键列的名字，这列的值就属于many-to-many的class类的ID值 --> <!---注释部分可能会引起XML格式错误，---> <set name="students" table="t_s_Connection"> <key> <column name="T_ID" /> </key> <many-to-many class="com.atguigu.hibernate.n2n.Student" column="S_ID"/> </set> </class> </hibernate-mapping>
student：
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.atguigu.hibernate.n2n.Student" table="STUDENT"> <id name="S_ID" type="java.lang.Integer"> <column name="S_ID" /> <generator class="native" /> </id> <property name="s_Name" type="java.lang.String"> <column name="S_NAME" /> </property> </class> </hibernate-mapping>
然后配置一下Hibernate.cfg.xml文件即可
单向的多对多关系，就是这样了，但是其的增删改查又有什么特点？？？这个稍后再探究
II双向的多对多关系如何配置
1在双方持久化类（就是teacher和student）中互相添加对方的对象集合，并且当中有一个需要实例化
例如：在teacher中添加private set<student>
在student中添加private set<teacher>=new hashSet<teacher>();
代码：teacher:
package com.atguigu.hibernate.n2n; import java.util.Set; public class Teacher { private Integer ID; private String Name; private Set<Student> students; public Integer getID() { return ID; } public void setID(Integer iD) { ID = iD; } public String getTea_Name() { return Name; } public void setTea_Name(String Name) { this.Name =Name; } public Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } }
student:
package com.atguigu.hibernate.n2n; import java.util.HashSet; import java.util.Set; public class Student { private Integer S_ID; private String s_Name; private Set<Teacher> teachers=new HashSet<Teacher>(); public Set<Teacher> getTeachers() { return teachers; } public void setTeachers(Set<Teacher> teachers) { this.teachers = teachers; } public Integer getS_ID() { return S_ID; } public void setS_ID(Integer s_ID) { S_ID = s_ID; } public String getS_Name() { return s_Name; } public void setS_Name(String s_Name) { this.s_Name = s_Name; } }
2在双方的持久化类中添加set和many-to-many设置
teacher.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"> <hibernate-mapping> <class name="com.atguigu.hibernate.n2n.Teacher" table="TEACHER"> <id name="ID" type="java.lang.Integer"> <column name="ID" /> <generator class="native" /> </id> <property name="Name" type="java.lang.String" access="field"> <column name="NAME" /> </property> <!-- name:set集合的名字 Table：中间表的名字 key--column:中间表的外键列的名字（可以放任意名字），就是指明中间表的外键列是当前持久化类的的ID属性 many-to-many的column：也是指定中间表的外键列的名字，这列的值就属于many-to-many的class类的ID值 --> <set name="students" table="t_s_Connection"> <key> <column name="T_ID" /> </key> <many-to-many class="com.atguigu.hibernate.n2n.Student" column="S_ID"/> </set> </class> </hibernate-mapping>
student.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"> <hibernate-mapping> <class name="com.atguigu.hibernate.n2n.Student" table="STUDENT"> <id name="S_ID" type="java.lang.Integer"> <column name="S_ID" /> <generator class="native" /> </id> <property name="s_Name" type="java.lang.String"> <column name="S_NAME" /> </property> <set name="teachers" table="t_s_Connection"> <key> <column name="S_ID"></column> </key> <many-to-many class="com.atguigu.hibernate.n2n.Teacher" column="T_ID"></many-to-many> </set> </class> </hibernate-mapping>
然后在Hibernate.cfg.xml文件配置一下mapping-resource即可
但是双向的多对多关系的增删改查又是怎样的呢？？
而且单向的多对多关系和多向的多对多关系两者有什么不同，有什么有缺点？？
标签：style blog http color io java for 文件 sp
原文地址：http://www.cnblogs.com/jeremy-blog/p/4013203.html
