Hibernate_Many-to-Many

昨天老师下午是打算讲Hibernate中 many-to-many 来着。可惜因为他从来不备课，所以啊，昨天又讲到一半就把自己给弄懵了.我们狂晕！！还是自己动手丰衣足食啦！

其实找些资料看一下，并没有想象的那么难，具体做法如下：

一，创建一个web工程，添加Hibernate 包(右键点击工程名称/Myeclipse/add Hibernate Capabilites/在弹出的对话框中选择next/next/在specify database connection details 中不将其选中,点击next/在java package选择一个包，如果没有就建一个(假如叫user),点击finish.

此时在user包中会看到一个名字叫HibernateSessionFactory.java类

二，在user包下，建立两个类，分别是Student.jave,Teacher.java

Student.jave

 

package user;

import java.util.HashSet;
import java.util.Set;

public class Student {
private Integer studentId;
private String studentName;
private Set<Teacher> teacherSet=new HashSet<Teacher>();
public Student(){}
public Integer getStudentId() {
 return studentId;
}
public void setStudentId(Integer studentId) {
 this.studentId = studentId;
}
public String getStudentName() {
 return studentName;
}
public void setStudentName(String studentName) {
 this.studentName = studentName;
}
public Set<Teacher> getTeacherSet() {
 return teacherSet;
}
public void setTeacherSet(Set<Teacher> teacherSet) {
 this.teacherSet = teacherSet;
}
}

Teacher.java

 

package user;

import java.util.HashSet;
import java.util.Set;

public class Teacher {
private Integer teacherId;
private String teacherName;
private Set<Student> studentSet=new HashSet<Student>();
public Teacher(){}
public Set<Student> getStudentSet() {
 return studentSet;
}
public void setStudentSet(Set<Student> studentSet) {
 this.studentSet = studentSet;
}
public Integer getTeacherId() {
 return teacherId;
}
public void setTeacherId(Integer teacherId) {
 this.teacherId = teacherId;
}
public String getTeacherName() {
 return teacherName;
}
public void setTeacherName(String teacherName) {
 this.teacherName = teacherName;
}
}

三，创建两个xml,分别为student.bm.ml,teacher.hbm.xml

student.bm.ml

 

<?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">
<!--
 Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
 <class name="user.Student" table="student" catalog="test">
  <id name="studentId" type="integer">
   <column name="studentId"></column>
   <generator class="native"></generator>
  </id>
  <property name="studentName" type="string">
   <column name="studentName"></column>
  </property>
  <set name="teacherSet" table="t_student_teacher" lazy="true" inverse="true" cascade="save-update">
   <key column="studentId"></key>
   <many-to-many class="user.Teacher" column="teacherId"  />
  </set>
 </class>
</hibernate-mapping>

 

teacher.hbm.xml

 

<?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">
<!--
 Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
 <class name="user.Teacher" table="teacher" catalog="test"><!--teacher class -->
  <id name="teacherId" type="integer"><!--class -->
   <column name="teacherId" /><!--table -->
   <generator class="native" />
  </id>
  <property name="teacherName" type="string"><!--class -->
   <column name="teacherName" /><!--table -->
  </property>
  <!-- -->
  <set name="studentSet" table="t_student_teacher" lazy="true" inverse="false" cascade="save-update"><!--中间表 -->
   <key column="teacherId"></key><!--左边表 -->
   <many-to-many class="user.Student" column="studentId"/><!--右边表 -->
  </set>
 </class>
</hibernate-mapping>

 

四，配置Hibernate.cfg.xml,配置之间需要向工程中添加连接数据库的驱动包(mysql-connector-java-3.1.7-bin.jar),如没有请下载

添加方法,右键点击工程名称/properties/java build path/Libraries/add external jars，然后选择包即可。

<?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="myeclipse.connection.profile">mysql</property>
 <property name="connection.url">
  jdbc:mysql://localhost/test?useUnicode=true&amp;characterEncoding=utf-8
 </property>
 <property name="connection.username">root</property>
 <property name="connection.password">123456</property>
 <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
 <property name="dialect">
  org.hibernate.dialect.MySQLDialect
 </property>
 <property name="show_sql">true</property>
 <mapping resource="user/student.hbm.xml" />
 <mapping resource="user/teacher.hbm.xml" />

</session-factory>

</hibernate-configuration>

五，创建一个类(Test),此类根据xml生成所需的表

package user;

import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;

public class Test {
 public static void main(String args[]) {
  Configuration cfg=new Configuration().configure();
  System.out.println("Configuration通过映射文件生成数据库的表");
  SchemaExport sc=new SchemaExport(cfg);
  sc.create(true, true);
  System.out.println("完成生成数据库表");
 }
}

之后在mysql中，会看到新生成的三张表，分别是teacher,student,t_student_teacher

六，写一个Save类，通过此类向表中插入数据

package user;

import org.hibernate.Session;
import org.hibernate.Transaction;

public class Save {
 static Session session;

 static Transaction tr;

 public static void main(String args[]) {
  session = HibernateSessionFactory.getSession();
  tr = session.beginTransaction();
  Student s1 = new Student();
  Student s2 = new Student();
  s1.setStudentName("aa学生");
  s2.setStudentName("bb学生");
  Teacher t1 = new Teacher();
  Teacher t2 = new Teacher();
  Teacher t3 = new Teacher();
  t1.setTeacherName("aa老师");
  t2.setTeacherName("bb老师");
  t3.setTeacherName("cc老师");

  s1.getTeacherSet().add(t3);
  
  s1.getTeacherSet().add(t1);
  s1.getTeacherSet().add(t2);
  
  s2.getTeacherSet().add(t1);
  s2.getTeacherSet().add(t2);
  
  t1.getStudentSet().add(s1);
  t1.getStudentSet().add(s2);

  t2.getStudentSet().add(s2);
  t2.getStudentSet().add(s1);
  
  t3.getStudentSet().add(s1);
  

  try {
   session.save(s1);
   session.save(s2);
   session.save(t1);
   session.save(t2);
   tr.commit();
  } catch (Exception e) {
   if (tr != null) {
    System.out.println("事务发生回滚");
    tr.rollback();
   }
   e.printStackTrace();
  } finally {
   HibernateSessionFactory.closeSession();
  }
 }

}
六,写一个Get类，通过此类可以将学生与老师的对应关系显示出来，从而看出many-to-many的关系

package user;

import java.util.Iterator;
import java.util.List;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.Transaction;

public class Get {
 static Session session;

 static Transaction tr;
 

 public static void main(String args[]) {
  Get g=new Get();
  g.Student_TeacherSet();
  

 }
//TeacherSet
 public void Student_TeacherSet() {
  try {
   session = HibernateSessionFactory.getSession();
   tr = session.beginTransaction();
   List list=session.createQuery("from Student s").list();
   for(int i=0;i<list.size();i++)
   {
    Student s=(Student)list.get(i);
    System.out.println("第"+(i+1)+"个学生名字是:"+s.getStudentName());
    
    Set<Teacher> set=s.getTeacherSet();
    Iterator it=set.iterator();
    int j=0;
    while(it.hasNext())
    {
     Teacher t=(Teacher)it.next();
     System.out.println("第"+(i+1)+"个学生下的第"+(++j)+"个老师："+t.getTeacherName());
    }
   }

  } catch (Exception e) {
   if (tr != null) {
    System.out.println("事务发生回滚");
    tr.rollback();
   }
   e.printStackTrace();
  } finally {
   HibernateSessionFactory.closeSession();
  }
 }

}