Map entities from a resource when written to the world.

crates/bevy_ecs/src/reflect/map_entities.rs

@@ -73,3 +73,28 @@ impl<C: Component + MapEntities> FromType<C> for ReflectMapEntities {
         }
     }
 }
+
+#[derive(Clone)]
+pub struct ReflectMapEntitiesResource {
+    map_entities: fn(&mut World, &mut SceneEntityMapper),
+}
+
+impl ReflectMapEntitiesResource {
+    pub fn map_entities(&self, world: &mut World, entity_map: &mut EntityHashMap<Entity>) {
+        SceneEntityMapper::world_scope(entity_map, world, |world, mapper| {
+            (self.map_entities)(world, mapper);
+        });
+    }
+}
+
+impl<R: crate::system::Resource + MapEntities> FromType<R> for ReflectMapEntitiesResource {
+    fn from_type() -> Self {
+        ReflectMapEntitiesResource {
+            map_entities: |world, entity_mapper| {
+                if let Some(mut resource) = world.get_resource_mut::<R>() {
+                    resource.map_entities(entity_mapper);
+                }
+            },
+        }
+    }
+}

crates/bevy_ecs/src/reflect/mod.rs

@@ -19,7 +19,7 @@ pub use bundle::{ReflectBundle, ReflectBundleFns};
 pub use component::{ReflectComponent, ReflectComponentFns};
 pub use entity_commands::ReflectCommandExt;
 pub use from_world::{ReflectFromWorld, ReflectFromWorldFns};
-pub use map_entities::ReflectMapEntities;
+pub use map_entities::{ReflectMapEntities, ReflectMapEntitiesResource};
 pub use resource::{ReflectResource, ReflectResourceFns};
 
 /// A [`Resource`] storing [`TypeRegistry`] for

crates/bevy_scene/src/dynamic_scene.rs

@@ -11,7 +11,7 @@ use bevy_utils::TypeIdMap;
 #[cfg(feature = "serialize")]
 use crate::serde::SceneSerializer;
 use bevy_asset::Asset;
-use bevy_ecs::reflect::ReflectResource;
+use bevy_ecs::reflect::{ReflectMapEntitiesResource, ReflectResource};
 #[cfg(feature = "serialize")]
 use serde::Serialize;
 
@@ -88,6 +88,10 @@ impl DynamicScene {
                 }
             })?;
 
+            if let Some(map_entities_reflect) = registration.data::<ReflectMapEntitiesResource>() {
+                map_entities_reflect.map_entities(world, entity_map);
+            }
+
             // If the world already contains an instance of the given resource
             // just apply the (possibly) new value, otherwise insert the resource
             reflect_resource.apply_or_insert(world, &**resource, &type_registry);