[SOLVED] I'm using realm DB and it has no Foreign keys .. is there any alternative solution?

I'm using realm DB and it has no Foreign keys .. is there any alternative solution?

guys i'm working on a android project for my DB course and i'm using realm DB but the problem is that i just found that realm has no foreign keys(realm is NOT a relational DB) so i was wondering if there is any other solution to use as a foreign key?

i was thinking about using class composition but would it work ?

Solution

Realm has the concept of "relationships" (otherwise called as "links").

To-one relationship:

public class A extends RealmObject {
    B b;
}

To many relationship:

public class A extends RealmObject {
    RealmList<B> bs;
}

And for either of those relationships, there exists an inverse relationship (Realm Java 3.5.0+)

public class A extends RealmObject {
    B b;

    RealmList<B> bs;
}

public class B extends RealmObject {
    @LinkingObjects("b")
    private final RealmResults<B> fromB = null;

    @LinkingObjects("bs")
    private final RealmResults<B> fromBs = null;
}

If an object is unmanaged, then insertOrUpdate()/copyToRealmOrUpdate() will insert both A and its instance B into the Realm.

If an object is managed, then the object you set as value must be managed as well.

A a = realm.createObject(A.class);
a.setB(realm.createObject(B.class)); // or copyToRealmOrUpdate(b) or .findFirst() etc