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RealmSet - Java SDK

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  • Method Limitations
  • Usage
  • Notifications

New in version 10.6.0.

You can use the RealmSet data type to manage a collection of unique keys. RealmSet implements Java's Set interface, so it works just like the built-in HashSet class, except managed RealmSet instances persist their contents to a realm. RealmSet instances that contain Realm objects actually only store references to those objects, so deleting a Realm object from a realm also deletes that object from any RealmSet instances that contain the object.

Because RealmSet implements RealmCollection, it has some useful mathematical methods, such as sum, min, and max. For a complete list of available RealmSet methods, see: the RealmSet API reference.

Method Limitations

You cannot use the following Realm methods on objects that contain a field of type RealmSet:

  • Realm.insert()

  • Realm.insertOrUpdate()

  • Realm.createAllFromJson()

  • Realm.createObjectFromJson()

  • Realm.createOrUpdateAllFromJson()

  • Realm.createOrUpdateObjectFromJson()

Usage

To create a field of type RealmSet, define an object property of type RealmSet<E>, where E defines the keys you would like to store in your RealmSet.

import io.realm.RealmObject;
import io.realm.RealmSet;
public class Frog extends RealmObject {
    String name;
    RealmSet<Snack> favoriteSnacks;
    // realm-required empty constructor
    public Frog() {}
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public RealmSet<Snack> getFavoriteSnacks() { return favoriteSnacks; }
    public void setFavoriteSnacks(RealmSet<Snack> favoriteSnacks) { this.favoriteSnacks = favoriteSnacks; }
}
import io.realm.RealmObject;
public class Snack extends RealmObject {
    private String name;
    public Snack() {}
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
}
Frog frog = realm.createObject(Frog.class);
frog.setName("George Washington");
// get the RealmSet field from the object we just created
RealmSet<Snack> set = frog.getFavoriteSnacks();
// add value to the RealmSet
Snack flies = realm.createObject(Snack.class);
flies.setName("flies");
set.add(flies);
// add multiple values to the RealmSet
Snack water = realm.createObject(Snack.class);
water.setName("water");
Snack verySmallRocks = realm.createObject(Snack.class);
verySmallRocks.setName("verySmallRocks");
set.addAll(Arrays.asList(water, verySmallRocks));
// check for the presence of a key with contains
Assert.assertTrue(set.contains(flies));
// check for the presence of multiple keys with containsAll
Snack biscuits = realm.createObject(Snack.class);
biscuits.setName("biscuits");
Assert.assertTrue(set.containsAll(Arrays.asList(water, biscuits)) == false);
// remove string from a set
set.remove(verySmallRocks);
// set no longer contains that string
Assert.assertTrue(set.contains(verySmallRocks) == false);
// deleting a Realm object also removes it from any RealmSets
int sizeOfSetBeforeDelete = set.size();
flies.deleteFromRealm();
// deleting flies object reduced the size of the set by one
Assert.assertTrue(sizeOfSetBeforeDelete == set.size() + 1);
import io.realm.RealmObject
import io.realm.RealmSet
open class Frog
    : RealmObject() {
    var name: String = ""
    var favoriteSnacks: RealmSet<Snack> = RealmSet<Snack>();
}
import io.realm.RealmObject
open class Snack : RealmObject() {
    var name: String? = null
}
val frog = realm.createObject(Frog::class.java)
frog.name = "Jonathan Livingston Applesauce"
// get the RealmSet field from the object we just created
val set = frog.favoriteSnacks
// add value to the RealmSet
val flies = realm.createObject(Snack::class.java)
flies.name = "flies"
set.add(flies)
// add multiple values to the RealmSet
val water = realm.createObject(Snack::class.java)
water.name = "water"
val verySmallRocks = realm.createObject(Snack::class.java)
verySmallRocks.name = "verySmallRocks"
set.addAll(listOf(water, verySmallRocks))
// check for the presence of a key with contains
Assert.assertTrue(set.contains(flies))
// check for the presence of multiple keys with containsAll
val biscuits = realm.createObject(Snack::class.java)
biscuits.name = "biscuits"
Assert.assertTrue(set.containsAll(Arrays.asList(water, biscuits)) == false)
// remove string from a set
set.remove(verySmallRocks)
// set no longer contains that string
Assert.assertTrue(set.contains(verySmallRocks) == false)
// deleting a Realm object also removes it from any RealmSets
val sizeOfSetBeforeDelete = set.size
flies.deleteFromRealm()
// deleting flies object reduced the size of the set by one
Assert.assertTrue(sizeOfSetBeforeDelete == set.size + 1)

Notifications

To subscribe to changes to a RealmSet, pass a SetChangeListener implementation to the RealmSet.addChangeListener method. Your SetChangeListener implementation must define an onChange() method, which accepts a reference to the changed RealmSet and a set of changes as parameters. You can access the number of items added to the set as well as the number of items removed from the set through the SetChangeSet parameter.

AtomicReference<Frog> frog = new AtomicReference<Frog>();
realm.executeTransaction(r -> {
    frog.set(realm.createObject(Frog.class));
    frog.get().setName("Jonathan Livingston Applesauce");
});
SetChangeListener<Snack> setChangeListener = new SetChangeListener<Snack>() {
    @Override
    public void onChange(@NotNull RealmSet<Snack> set, SetChangeSet changes) {
        Log.v("EXAMPLE", "Set changed: " +
                changes.getNumberOfInsertions() + " new items, " +
                changes.getNumberOfDeletions() + " items removed.");
    }
};
frog.get().getFavoriteSnacks().addChangeListener(setChangeListener);
realm.executeTransaction(r -> {
    // get the RealmSet field from the object we just created
    RealmSet<Snack> set = frog.get().getFavoriteSnacks();
    // add value to the RealmSet
    Snack flies = realm.createObject(Snack.class);
    flies.setName("flies");
    set.add(flies);
    // add multiple values to the RealmSet
    Snack water = realm.createObject(Snack.class);
    water.setName("water");
    Snack verySmallRocks = realm.createObject(Snack.class);
    verySmallRocks.setName("verySmallRocks");
    set.addAll(Arrays.asList(water, verySmallRocks));
});
var frog :Frog? = null
realm.executeTransaction { r: Realm? ->
    frog = realm.createObject(Frog::class.java)
    frog?.name = "Jonathan Livingston Applesauce"
}
val setChangeListener: SetChangeListener<Snack>
        = SetChangeListener<Snack> { set, changes ->
    Log.v("EXAMPLE", "Set changed: " +
            changes.numberOfInsertions + " new items, " +
            changes.numberOfDeletions + " items removed.")
}
frog?.favoriteSnacks?.addChangeListener(setChangeListener)
realm.executeTransaction { r: Realm? ->
    // get the RealmSet field from the object we just created
    val set = frog!!.favoriteSnacks
    // add value to the RealmSet
    val flies = realm.createObject(Snack::class.java)
    flies.name = "flies"
    set.add(flies)
    // add multiple values to the RealmSet
    val water = realm.createObject(Snack::class.java)
    water.name = "water"
    val verySmallRocks = realm.createObject(Snack::class.java)
    verySmallRocks.name = "verySmallRocks"
    set.addAll(Arrays.asList(water, verySmallRocks))
}

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