Hibernate Bidirectional Many to Many implementation

Question

I am new to hibernate and I want to implement something like this in hibernate. To be able to do this, I am getting problem in setting the xml mapping file. If someone can help me, it would be very nice as this is just of proof of concept I am trying to do, I have much complicated things to do.Thanks

public class Course implements java.io.Serializable 
{
    private long courseId;
    private String courseName;
    private Set <Student> Stu = new HashSet <Student>();
}

public class Student implements java.io.Serializable 
{

    private long studentId;
    private String studentName;
    private Set<Course> courses = new HashSet<Course>();
}

But in the database, I want 3 table to be created Student,Course and StudentCourse

              Student----->StudentCourse<------Course 
            StudentId      StudentId          CourseId     
                            CourseId

What I want is that when I do

 Course C1=(Course)session.get(Course.class,CourseId)

I get the specified course and by doing

  Set <Student> StudentsEnrolled=C1.getStu();

I get all students enrolled in that course

Similary When I do

Student S1=(Student)session.get(Student.class,StudentId)

I get the specified student and by doing

Set <Course> CoursesEnrolled=S1.getCourses();

I get all courses the specified student has taken

Only a hint: When using hibernate you can use Annotations to descripe the mapping instad of XML. It profides the same features, but it is not so mutch to write. — Ralph, Dec 04 '10 at 18:40

Liviu T. · Accepted Answer · 2010-12-04T15:29:45.487

Take a look at this

<hibernate-mapping>
    <class name="com.vaannila.student.Student" table="STUDENT">
        <meta attribute="class-description">This class contains student details.</meta>
        <id name="studentId" type="long" column="STUDENT_ID">
            <generator class="native" />
        </id>
        <property name="studentName" type="string" length="100" not-null="true" column="STUDENT_NAME" />
        <set name="courses" table="STUDENT_COURSE" cascade="all">
            <key column="STUDENT_ID" />
            <many-to-many column="COURSE_ID"  class="com.vaannila.student.Course" />
        </set>
    </class>
</hibernate-mapping>

<hibernate-mapping>
    <class name="com.vaannila.student.Course" table="COURSE">
        <meta attribute="class-description">This class contains course details.</meta>
        <id name="courseId" type="long" column="COURSE_ID">
            <generator class="native"/>
        </id>
        <property name="courseName" type="string" column="COURSE_NAME"/>
        <set name="students" table="STUDENT_COURSE" cascade="all">
            <key column="COURSE_ID" />
            <many-to-many column="STUDENT_ID"  class="com.vaannila.student.Student" />
        </set>
    </class>
</hibernate-mapping>

Well if you mirror the set in the other class like this doesn't it work?

octav · Answer 2 · 2010-12-04T17:10:55.313

1

What you are looking for is very similar with the example stated here: http://technicalmumbojumbo.wordpress.com/2007/09/25/investigating-hibernate-associations-many-to-many/

It starts with a unidirectional relationship, and at the end it defines the mappings for the bidirectional one.

Hope this helps,
Octav

=====================================
Don't forget you have to decide which entity is the owner of this relationship: Student or Course. Once you've decided that, the Hibernate mapping of the "owned" entity needs to have the "inverse" flag set to true.
That's exactly how it's described in the link above, if you check the Hibernate mapping for the Phone entity, at the end of the article.

edited Dec 04 '10 at 17:10

answered Dec 04 '10 at 12:09

octav

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In both of the links shown above, one of the table has the set while the other don't have. I want a situation where both table hold the sets – Noor Dec 04 '10 at 12:26
Check further down the page, as the initially unidirectional relationship is changed to a bidirectional one. Paragraph starts with: "Moving on, let’s get a bi-directional many-to-many association going." – octav Dec 04 '10 at 12:30

Hibernate Bidirectional Many to Many implementation

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