hibernate多对多关联映射

知识点： 

【 

多对多(teacher - student) 

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。 

<set name="teacher" table="teacher_student"> 

 <key column="teacher_id"/> 

 <many-to-many class="Student" column="student_id"/> 

</set> 



】 


照样实现步骤如下： 


第一步：搭建hibernate运行所需的环境及*.jar 具体搭建见上面的博客 


hibernate.cfg.xml: 

<!DOCTYPE hibernate-configuration PUBLIC 

 "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 

 "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> 


<hibernate-configuration> 

 <session-factory> 

 <property name="show_sql">true</property> 


 <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property> 

 <!-- jdbc:mysql:///test 以下表示localhost 3306 test：数据库--> 

 <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/student?useUnicode=true&characterEncoding=UTF-8</property> 

 <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property> 

 <property name="hibernate.connection.username">root</property> 

 <property name="hibernate.connection.password">liyong</property> 


 <!-- 下面指定方言 --> 

 <property name="dialect">org.hibernate.dialect.MySQLDialect</property> 

 <!-- 下面指定是否让hibernate产生ddl语句 DDL:数据定义语言--> 

 <property name="hbm2ddl.auto">update</property> 


 <mapping resource="com/liyong/domain/Student.hbm.xml"/> 

 <mapping resource="com/liyong/domain/Teacher.hbm.xml"/> 


 </session-factory> 

</hibernate-configuration> 



第二步：编程实体类Student.java 和Teacher.java 


Student.java 


public class Student { 


 private int id; 

 private String name; 

 private Set<Teacher> teachers; 


 public int getId() { 

 return id; 

 } 


 public void setId(int id) { 

 this.id = id; 

 } 


 public String getName() { 

 return name; 

 } 


 public void setName(String name) { 

 this.name = name; 

 } 


 public Set<Teacher> getTeachers() { 

 return teachers; 

 } 


 public void setTeachers(Set<Teacher> teachers) { 

 this.teachers = teachers; 

 } 


} 


Teacher.java 

public class Teacher { 


 private int id; 

 private String name; 

 private Set<Student> students; 


 public int getId() { 

 return id; 

 } 


 public void setId(int id) { 

 this.id = id; 

 } 


 public String getName() { 

 return name; 

 } 


 public void setName(String name) { 

 this.name = name; 

 } 


 public Set<Student> getStudents() { 

 return students; 

 } 


 public void setStudents(Set<Student> students) { 

 this.students = students; 

 } 


} 


第三步：编写类的映射文件Student.hbm.xml、Teacher.hbm.xml 


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 package="com.liyong.domain"> 

 <class name="Teacher"> 

 <!-- 生成主键 以natvie 自增长--> 

 <id name="id"> 

 <generator class="native" /> 

 </id> 

 <property name="name" /> 

 <!-- 下面的table指定中间表名table --> 

 <set name="students" table="teacher_student"> 

 <key column="teachar_id"/> 

<！--下面是所映射的外键--> 

 <many-to-many class="Student" column="student_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 package="com.liyong.domain"> 


 <class name="Student"> 

 <!-- 生成主键 以natvie 自增长--> 

 <id name="id"> 

 <generator class="native" /> 

 </id> 

 <property name="name" /> 

 <!-- 下面的table指定中间表名table --> 

 <set name="teachers" table="teacher_student"> 

 <!--<key column="student_id"/>表示查询teachers这个集合中的数据时根据通过反射找到Teacher类所映射的表中的 外键student_id列对应去查询 --> 

 <key column="student_id"/> 

 <!-- teachar_id 是映射中间表的列名 可以看成就是映射的外键--> 

 <many-to-many class="Teacher" column="teachar_id"/> 

 </set> 

 </class> 


</hibernate-mapping> 


第四步：编程测试 


public class ManyToManyTest { 


 public static void main(String[] args) { 

 //add(); 

 query(1); 

 } 


 @Test 

 public static void add() { 

 Session s = null; 

 Transaction tx = null; 

 try { 

 Set<Teacher> ts = new HashSet<Teacher>(); 


 Teacher t1 = new Teacher(); 

 t1.setName("t1 name"); 

 ts.add(t1); 


 Teacher t2 = new Teacher(); 

 t2.setName("t2 name"); 

 ts.add(t2); 


 Set<Student> ss = new HashSet<Student>(); 

 Student s1 = new Student(); 

 s1.setName("s1"); 

 ss.add(s1); 


 Student s2 = new Student(); 

 s2.setName("s2"); 

 ss.add(s2); 


 t1.setStudents(ss); 

 t2.setStudents(ss); 

 /* 不能同时学生和老师添加集合数据 

 s1.setTeachers(ts); 

 s2.setTeachers(ts);*/ 


 s = HibernateUtil.getSession(); 

 tx = s.beginTransaction(); 

 s.save(t1); 

 s.save(t2); 

 s.save(s1); 

 s.save(s2); 

 tx.commit(); 

 } finally { 

 if (s != null) 

 s.close(); 

 } 

 } 

 @Test 

 public static void query(int id) 

 { 

 Session s = null; 

 try { 


 s=HibernateUtil.getSession(); 

 Teacher teacher=(Teacher)s.get(Teacher.class, id); 

 Set<Student> students=teacher.getStudents(); 

 System.out.println("teacher :"+teacher.getName()); 

 for(Student student:students) 

 { 

 System.out.println("name_:"+student.getName()); 

 } 


 }catch (Exception e) { 

 throw new RuntimeException("error"); 

 }finally{ 

 if(s!=null) 

 { 

 s.close(); 

 } 

 } 


 } 

} 


第五：测试 


源码见附件：