Self-Referential Relationships

Relationships can now optionally point to their own entity by setting the allow_self_referential attribute on the #[relationship] macro.

By default pointing a relationship to its own entity will log a warning and remove the component. However, self-referential relationships are semantically valid in many cases: Likes(self), EmployedBy(self), TalkingTo(self), Healing(self), and many more.

Usage

To allow a relationship to point to its own entity, add the allow_self_referential attribute:

#[derive(Component)]
#[relationship(relationship_target = PeopleILike, allow_self_referential)]
pub struct LikedBy(pub Entity);

#[derive(Component)]
#[relationship_target(relationship = LikedBy)]
pub struct PeopleILike(Vec<Entity>);

Now entities can have relationships that point to themselves:

let entity = world.spawn_empty().id();
world.entity_mut(entity).insert(LikedBy(entity));

// The relationship is preserved
assert!(world.entity(entity).contains::<LikedBy>());
assert!(world.entity(entity).contains::<PeopleILike>());