CODEWITHSUNDEEP
javahibernate
Didar Burmaganov
Didar Burmaganov

Reputation: 632

Hibernate inheritance query

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?

Upvotes: 1

Views: 544

Answers (1)

JB Nizet
JB Nizet

Reputation: 692281

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.

Upvotes: 2

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