Question

I am working on some academic task and I’m stuck. The situation is as follows:
I have three simple database tables and Java @Entity classes generated from them.

Table Mark:
STUDENT_ID (PK)
SUBJECT_ID (PK)
MARK

public class Mark implements Serializable {
    private BigDecimal mark;
    @Id
    @Column(name = "STUDENT_ID", nullable = false, insertable = false, updatable = false)
    private BigDecimal studentId;
    @Id
    @Column(name = "SUBJECT_ID", nullable = false, insertable = false, updatable = false)
    private BigDecimal subjectId;
    @ManyToOne
    @JoinColumn(name = "SUBJECT_ID")
    private Subject subject;
    @ManyToOne
    @JoinColumn(name = "STUDENT_ID")
    private Student student;
(...)
}

Table Student:
INDEX_NO (PK)
FNAME
LNAME
FACULTY_ID

public class Student implements Serializable {
    @Column(name = "FACULTY_ID", nullable = false)
    private BigDecimal facultyId;
    @Column(nullable = false, length = 20)
    private String fname;
    @Id
    @Column(name = "INDEX_NO", nullable = false)
    private BigDecimal indexNo;
    @Column(nullable = false, length = 20)
    private String lname;
    @OneToMany(mappedBy = "student")
    private List<Mark> marksList1;
(...)
}

Table Student:
ID (PK)
NAME

public class Subject implements Serializable {
    @Id
    @Column(nullable = false)
    private BigDecimal id;
    @Column(nullable = false, length = 60)
    private String name;
    @OneToMany(mappedBy = "subject")
    private List<Mark> marksList;
(...)
}

The task is to obtain two lists:
1. The list of students which does not have marks from all of the subjects yet.
2. The list of subjects from which particular student does not have a mark.

I am not too good at SQL, so I have problem with query construction. It can be solved by any JPA-like way, i.e. JPQL, Criteria API.

So I am asking you for a help.
Thank you for your interest.

Answer 1

I’m not sure if this is correct but maybe this can help you solve your issue. The size() function in JPQL can count a collection.

These are 2 JPQL query’s

1)

select m.student
from Mark m
where size(m.subject) <> 
    size(select s from Subject s)

2)

select s
from Subject s
where s not in 
    (select m.s from Mark m where m.student.indexNo = :indexNo) 

:indexNo is then the student’s id that should be set using a parameter.