ComponentHook based Parent/Children Management

crates/bevy_hierarchy/src/family.rs

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+use crate::{OneToManyEvent, OneToManyMany, OneToManyOne};
+
+/// A familial relationship
+#[cfg_attr(feature = "reflect", derive(bevy_reflect::Reflect))]
+pub struct Family;
+
+/// Holds a reference to the parent entity of this entity.
+/// This component should only be present on entities that actually have a parent entity.
+///
+/// Parent entity must have this entity stored in its [`Children`] component.
+/// It is hard to set up parent/child relationships manually,
+/// consider using higher level utilities like [`BuildChildren::with_children`].
+///
+/// See [`HierarchyQueryExt`] for hierarchy related methods on [`Query`].
+///
+/// [`HierarchyQueryExt`]: crate::query_extension::HierarchyQueryExt
+/// [`Query`]: bevy_ecs::system::Query
+/// [`BuildChildren::with_children`]: crate::child_builder::BuildChildren::with_children
+pub type Parent = OneToManyOne<Family>;
+
+/// Contains references to the child entities of this entity.
+///
+/// Each child must contain a [`Parent`] component that points back to this entity.
+/// This component rarely needs to be created manually,
+/// consider using higher level utilities like [`BuildChildren::with_children`]
+/// which are safer and easier to use.
+///
+/// See [`HierarchyQueryExt`] for hierarchy related methods on [`Query`].
+///
+/// [`HierarchyQueryExt`]: crate::query_extension::HierarchyQueryExt
+/// [`Query`]: bevy_ecs::system::Query
+/// [`BuildChildren::with_children`]: crate::child_builder::BuildChildren::with_children
+pub type Children = OneToManyMany<Family>;
+
+/// An [`Event`] that is fired whenever there is a change in the world's hierarchy.
+///
+/// [`Event`]: bevy_ecs::event::Event
+pub type HierarchyEvent = OneToManyEvent<Family>;