hibernate关系映射（多对多）

多对多关系（学生Student，课程Course）

学生类的定义以及hbm文件的配置如下

public class Student {
    private int id;
    private String name;
    private Set<Course> courses = new HashSet<Course>();
}

<?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 >
    <class name="com.zlt.hibernatedemo.Student" table="student">
        <id name="id" column="id">
            <generator class="increment"></generator>
        </id>
        
        <property name="name" type="java.lang.String">  
            <column name="name" length="50" />  
        </property>
        
        <set name="courses" table="score" cascade="all">
            <key column="studentid"></key>
            <many-to-many class="com.zlt.hibernatedemo.Course" column="courseid"/>
        </set>
    </class>

</hibernate-mapping>

课程类的定义以及hbm文件的配置如下

public class Course {
    private int id;
    private String courseName;
    private Set<Student> students = new HashSet<Student>();
}

<?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 >
    <class name="com.zlt.hibernatedemo.Course" table="course">
        <id name="id" column="id">
            <generator class="increment"></generator>
        </id>
        
        <property name="courseName"></property>
        
        <set name="students" table="score">
            <key column="courseid"></key>
            <many-to-many class="com.zlt.hibernatedemo.Student" column="studentid"/>
        </set>
        
    </class>

</hibernate-mapping>

测试程序

public class HibernateTest {
    public static void main(String[] args) {
        Session session = HibernateFactory.currentSession();
        Transaction tx = session.beginTransaction();
        
        
        Student student1 = new Student();
        student1.setName("student1");
        
        Student student2 = new Student();
        student2.setName("student2");
        
        Course course1 = new Course();
        course1.setCourseName("course1");
        
        Course course2 = new Course();
        course2.setCourseName("course2");
        
        //由于使用了默认的inverse（false），所以两端都可以维护关联关系
        student1.getCourses().add(course1);
        student1.getCourses().add(course2);
        

        session.save(student1);
        //student设置了级联，所以不需要额外的插入course
//        session.save(course1);
//        session.save(course2);
        
        tx.commit();
        session.close();
        
    }
}

结果

如果多对多辅助表中还有其他的属性，就得把多对多关系拆分成两个一对多关系

学生Student

public class Student {
    private int id;
    private String name;
    private Set<Score> courses = new HashSet<Score>();    
}

课程Course

public class Course {
    private int id;
    private String courseName;
    private Set<Score> scores = new HashSet<Score>();
}

成绩Score

public class Score {
    private int id;
    private Student student;
    private Course course;
    
    //额外的属性
    private int score; 
}