Hibernate inheritance query

Question

I have 4 entities:

User, Teacher, Student, Course

and 4 tables:

t_user, t_teacher_course, t_student_course, t_course

Teacher and Student extends User (with descriminators) and have @ManyToMany relationship with Course (User do NOT have) Teacher's relations stored in t_teacher_course and Student's relations stored in t_student_course.

Now i want to select all users with courses (if they exists) in one query select u from User u left join fetch u.courses c (notice that User do not have courses) This select generated something like this:

select
    ...
from
    T_USER user0_ 
left outer join
    T_TEACHER_COURSE course1_ 
        on user0_.USERID_=courses1_.TEACHER_ 
left outer join
    T_COURSE course2_ 
        on courses1_.LANE_=course2_.COURSENAME_ 
where
    user0_.GROUP_=?

As you can see clearly Hibernate did NOT join with t_student_course table

I am using Hibernate 4.1Final

Question: Does Hibernate support such queries

a) if supports then why it didn't fetched courses for Student entity?

b) if do not support than how can i select all users with their courses using JPQL?

JB Nizet · Accepted Answer · 2012-06-19 11:56:56Z

2

Since u.courses could be student.courses or teacher.courses, Hibernate resolves the ambiguity by choosing the first (or last) association with this name in its metadata.

It might work if the name of the courses collection is not the same in both subclasses. For example, you could define Student.attendedCourses and Teacher.teachedCourses.

Otherwise, you'll have to issue two queries (one for teachers and one for students), and join the result lists. Or you'll have to pull up the association in the User entity.

edited Jun 19, 2012 at 11:56

answered Jun 19, 2012 at 7:37

JB Nizet

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1 Comment

Didar Burmaganov Over a year ago

Uau! Renaming fields solved problem! Thank you very much! Before your answer i needed to make 3 selects. I think Hibernate should warn about ambiguity

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