Hibernate Mapping of nested collection in java to mapping table through java annotation?

Question

I am facing difficulty to write hibernate mapping with java annotation for problem as given below.

Problem:

Tables

Table:Courses_Teachers
columns:
id
course_id
teacher_id
year(academic year)

Table: Courses_Students
columns:
id
course_id
student_id
year(academic year)

Table: Courses_Teachers_Students
course_teacher_id
course_student_id

Classes

class Student {
    Map<Course,List<Teacher>> courseTeachersMap;  
}

Requirements

A course can be taught by multiple teachers to same student group .
A course is assigned to a grade level.
A grade level can have multiple student groups who are assigned different set of teachers for a course.

Please suggest me how to specify annotation for courseTeachersMap property in class student.

Pascal Thivent · Accepted Answer · 2010-10-03 00:50:33Z

2

It is possible to map a ManyToMany association using a Map, and a typicall use case for this kind of mapping is when you have a ternary association. For example, if you have:

STUDENT_TEACHER_COURSE
STUDENT_ID(FK, PK)
TEACHER_ID(FK, PK)
COURSE_ID (FK, PK)

Then you could define the following mapping (assuming you're using a Hibernate Annotations < 3.5):

@Entity
public class Student {
    ...
    @ManyToMany
    @JoinTable(
        name="STUDENT_TEACHER_COURSE", 
        joinColumns= { @JoinColumn(name="STUDENT_ID") },
        inverseJoinColumns= { @JoinColumn(name="TEACHER_ID") }
    )
    @MapKeyManyToMany(joinColumns = @JoinColumn(name="COURSE_ID",unique = false))
    protected Map<Course,Teacher> teachers ;
    ...
}

But I don't think you can have a "nested" List<Teacher> as value inside the Map, I don't think Hibernate can map that and I'd consider getting the List from an entity instead.

References

Hibernate Annotations 3.4 Reference Guide
- 2.4.6.2.2. Map
Hibernate Annotations 3.5 Reference Guide
- 2.2.5.3.4. Indexed collections (List, Map)

Resources

edited Oct 3, 2010 at 0:50

answered Oct 2, 2010 at 20:19

Pascal Thivent

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5 Comments

Pascal Thivent Over a year ago

@Arthur Thanks. Do you see/know any better approach? What the OP wants looks very exotic to me.

Arthur Ronald Over a year ago

Your solution sounds good. But if he want an exotic mapping, he should use a lot of wrappers @Embeddable classes. I hope he provide some information about your approach.

Arthur Ronald Over a year ago

When i said A lot of relationships i refer to the mapping provided by @Maddy.Shik :)

Maddy.Shik Over a year ago

Thanks for solution. As u suggested approach i am following is little exotic and nested collection is also not possible with hibernate. You mentioned to use Entity instead of list, that is possible only if i use Class corresponding to mapping table which doesn't seem in accordance with coding principles. Can u please suggest your approach?

Maddy.Shik Over a year ago

Java Map will not allow non unique key. So only one course-teacher pair can be retrieved which will not fit my requirement.

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