Linked query for contains purpose

[Mohit Singh Kanwal]

Hi,

Just wanted to check if this approach is correct in terms of doing a linked query.

class Student {

    private int id;

}

class StudentCouncil {

    private RealmList<Student> members;

}

For  a student with id = 12, is this correct?

RealmQuery<StudentCouncil> query = realm.where(StudentCouncil.class)

                                   .equalTo("members.id", 12).findAll() // returns 2 rows

However, to my surprise I find that 

RealmQuery<StudentCouncil> query = realm.where(StudentCouncil.class)

                                        .notEqualTo("members.id", 12).findAll() // returns 3 rows

There are 3 councils and student is a member of only 2, and not a member of only 1 council. Is this correct? Or a I missing something.

Realm Version - 0.83.1

Regards

Mohit

[Kenneth Geisshirt]

Hi,

Link queries can be a bit tricky. Say you have:

1. four students: 0:id=11, 1:id=12, 2:id=13, 3:id=14
2. three councils: 0: {0, 1}, 1: {0, 2}, 2:{1, 3}

The query realm.where(StudentCouncil.class).notEqualTo("members.id", 12) should be read as "give me all StudentCouncils with at least one member with id != 12". As all three councils have at least a number with id != 12 (council 0: both, council 1: both, council: one), the three council objects are returned.

In your case, you are probably better off by doing:

for (StudentCouncil sc : realm.allObjects(StudentCouncil) {
if (sc.getMembers().where().equalTo("id", 12).count() == 0) {
// student 12 not member - hurrah!
}
}

Best,
Kenneth

--
Kenneth Geisshirt
Member of technical staff

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