why children only one parent? how to share child

[huang12zheng]

If I want to share a child, for example, both A and B can set the value of a bin, how can I do that?

and children only have one parent is as follow:

https://github.com/bevyengine/bevy/blob/main/crates/bevy_hierarchy/src/child_builder.rs#L965-L995

/// Tests what happens when all children are removed from a parent using world functions
    #[test]
    fn children_removed_when_empty_world() {
        let mut world = World::default();
        let entities = world
            .spawn_batch(vec![C(1), C(2), C(3)])
            .collect::<Vec<Entity>>();

        let parent1 = entities[0];
        let parent2 = entities[1];
        let child = entities[2];

        // push child into parent1
        world.entity_mut(parent1).push_children(&[child]);
        assert_eq!(
            world.get::<Children>(parent1).unwrap().0.as_slice(),
            &[child]
        );

        // move only child from parent1 with `push_children`
        world.entity_mut(parent2).push_children(&[child]);
        assert!(world.get::<Children>(parent1).is_none());

        // move only child from parent2 with `insert_children`
        world.entity_mut(parent1).insert_children(0, &[child]);
        assert!(world.get::<Children>(parent2).is_none());   ///<<<<<<<<<<<<<

        // remove only child from parent1 with `remove_children`
        world.entity_mut(parent1).remove_children(&[child]);
        assert!(world.get::<Children>(parent1).is_none());
    }

[nicopap]

You can always make your own componet

#[derive(Component)]
struct BinParents(Vec<Entity>);

Bevy's Parent and Children component are only meant to be used with Visibility and Transform. Because of this, each entity is limited to only a single parent.

But nothing prevents you from making your own Component that acts like a Parent but is a different component.

[rlidwka]

If I want to share a child, for example, both A and B can set the value of a bin, how can I do that?

Because bevy does not support traditional american values (so traditional family with two parents for each child is a thing of the past). Just look what discord logo we had on 4th of July!

Jokes aside, bevy hierarchy is designed to be a tree (or rather a forest strictly speaking, because multiple root nodes), which requires only one parent node by design. It's much simpler and faster to traverse than a generic graph, and almost nobody needs latter.

If you want a generic dependency graph, you can use custom components (wrapping Vec<Entity> as described above), or store your relations elsewhere (for example, insert HashMap<Entity, Entity> as a separate resource).

[huang12zheng]

a impls(The quality of the code is not guaranteed)
https://github.com/huang12zheng/bevy_parents_childs