Many-to-many and composite keys examples?

[José Román Bilbao Castro]

Hi all,

Can anybody point me towards examples using both things (not necessarily together, I am looking for independent examples).

Thanks in advance,

Jose

[Christian Melchior]

Hi José

Realm currently doesn't support composite keys, so right now the workaround would be to create a calculated key you manually keep up to date whenever you change any of the composite key values:

public MyObj extends RealmObject {

@PrimaryKey
private String compositeKey;

private int int1;
private int int2;

// Getters and setters

public static String getCompositeKey(MyObj obj) {
return Integer.toString(obj.getInt1()) + Integer.toString(obj.getInt2());
}
}

realm.beginTransaction();
myObj.setInt1(42);
myObj.setInt2(43);
myObj.setCompositeKey(MyObj.getCompositeKey(myObj));
realm.commitTransaction();

This is not ideal and is something we want to fix. You can follow progress on that here: https://github.com/realm/realm-java/issues/1129


Regarding many-to-many relations, then you have to keep in mind that Realm is not a relational database, so the standard way of having to create a many-to-many table doesn't apply here. Instead you can just do the following:


public class Foo extends RealmObject {
private RealmList<Bar> bars;

public void setBars(ReamList<Bar> bars) {
this.bars = bars;
}

public RealmList<Bar> getBars() {
return bars;
}
}

public class Bar extends RealmObject {
private RealmList<Foo> foos;

public void setFoos(ReamList<Foo> foos) {
this.foos = foos;
}

public RealmList<Foo> getFoos() {
return foos;
}
}

I hope that can get you started.

--
Christian Melchior
Senior Android Developer

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