The best way to configure the student course table in Hibernate

I have a question days ago on how to configure the student course relations. The main concern is how to express the score attribute. Finally, I find the following solution. To Configure it as a one-to-many map. The key is the course entity, and the value is the score(simple element).


I finally got the following solution:

public class Student implements java.io.Serializable {
    // Fields
    private String id;
    private Clazz clazz;
    private String studentName;
    private Integer studentAge;
    private Map courseScoreMap = new HashMap(0);

    ... omit the setters and getters

}


public class Course implements java.io.Serializable {
    // Fields
    private String id;
    private String courseName;

    // omit the setters and getters
}


public class Clazz implements java.io.Serializable {
    // Fields

    private String id;
    private String clazzName;
    private Set students = new HashSet(0);

    // omit the setters and getters
}

The following is the HBM file:

<hibernate-mapping package="com.hipposoft.school.domain">
    <class name="Clazz" table="clazz">      
        <id name="id" type="string">
            <column name="id" length="32">
            <generator class="uuid.hex"></generator>
        </column>
        <property name="clazzName" type="string">
            <column name="clazz_name" length="100">
        </column>
        <set name="students" inverse="true" cascade="all">
            <key>
                <column name="clazz_id" length="32" not-null="true">
            </column>
            <one-to-many class="Student">
        </one-to-many>
    </key>
</set>

<hibernate-mapping package="com.hipposoft.school.domain">
    <class name="Course" table="course">
        <id name="id" type="string">
            <column name="id" length="32">
            <generator class="uuid.hex"></generator>
        </column>
        <property name="courseName" type="string">
            <column name="course_name" length="100">
        </column>
    </property>
</id>

<hibernate-mapping package="com.hipposoft.school.domain">
    <class name="Student" table="student">
        <id name="id" type="string">
            <column name="id" length="32">
            <generator class="uuid.hex"></generator>
        </column>      
        <many-to-one name="clazz" class="Clazz" fetch="select">
            <column name="clazz_id" length="32" not-null="true">
        </column>
        <property name="studentName" type="string">
            <column name="student_name" length="100" not-null="true">
        </column>
        <property name="studentAge" type="integer">
            <column name="student_age">
        </column>
        <map name="courseScoreMap" cascade="all-delete-orphan" table="student_course_select">
            <key column="student_id"/>
            <map-key-many-to-many class="Course" column="course_id"/>
            <element type="double" column="score" />
        </map>
    </class>
</hibernate-mapping>



The following is the test code:

public void testMap() throws Exception{

    Session session = HibernateSessionFactory.getSession();

    session.beginTransaction();

    Clazz clazz = new Clazz();
    clazz.setClazzName("Gao San");

    Student s = new Student(clazz,"James");
    clazz.getStudents().add(s);

    // save the student and the class
    session.save(clazz);

    Course course = new Course("语文");
    session.save(course);

    session.flush();

    s.getCourseScoreMap().put(course, new Double(80.5));

    // save the course score
    session.update(s);

    session.getTransaction().commit();
}

In the new way, the above code is easy to write and read, as it is very natual to do so. And also the disadvantage is that we can not config a reverse relation to let a course associate to a student set, as hibernate didn't support that.