JPQL Multiple Left Joins on Unrelated Classes

Question

I have three tables with columns (bad fake names):

STUDENT (student_id)
STUDENT_UNIQUE_INFO (student_unique_info_id, student_id)
STUDENT_OTHER_INFO (student_other_info_id, student_id)

I wish I could change the schema but I can't. Some students don't have unique_info and/or other_info.

My result set would be like:

STUDENT_ID | STUDENT_UNIQUE_INFO_FIELDS... | STUDENT_OTHER_INFO_FIELDS...

Where the fields could sometimes be null if the student didn't have any.

Problem is most examples would have STUDENT containing the IDs of the other tables, I don't have that option.

I tried something like (outputting to a new obj that takes in all 3 of the tables used to join this thing)

SELECT NEW path.to.outputObj(S,
       (SELECT SUI
       FROM path.to.SUI SUI
       WHERE S.studentId = SUI.studentId),
       (SELECT SOI
       FROM path.to.SOI SOI
       WHERE S.studentId = SOI.studentId))
       FROM STUDENT S

But it blew up because some students have multiple entries in student_other_info.

java.sql.SQLException: Subquery returns more than 1 row

I'm just a bit lost at how to even go about this.

Answer 1

You should map those other two tables as lists that could contain 0..n rows for each student.

class Student {
   @OneToMany(mappedBy = "student");
   List<StudentUniqueInfo> studentUniqueInfoList;

   @OneToMany(mappedBy = "student");
   List<StudentOtherInfo> studentOtherInfoList;
   ...
}

And then StudentUniqueInfo.java and StudentOtherInfo.java would each have a field

 @JoinColumn(name = "STUDENT_ID")
 private Student student;