How can I safely query components (like Window) inside an on_insert hook in Bevy 0.17?

[mrknorman]

Context

I’m updating my project from Bevy 0.16 → 0.17, and ran into a problem with lifecycle hooks and the new DeferredWorld API.

In 0.16 I used to do this inside an on_insert:

fn on_insert(mut world: DeferredWorld, ctx: HookContext) {
    // Find the primary window
    let Some(window) = world.iter_entities()
        .find_map(|e| e.get::<Window>().cloned())
    else {
        warn!("No window found!");
        return;
    };

    info!("Window size: {}x{}", window.width(), window.height());
}

That worked fine, but iter_entities() is now deprecated in 0.17.
The migration guide says to use world.query::<EntityRef>().iter(&world), but that doesn’t compile with DeferredWorld because it requires a &mut World or an existing QueryState.

Is there a safe way to query components (e.g. Window with PrimaryWindow) from inside an on_insert hook now?

I’ve explored:

• world.query::<&Window, With<PrimaryWindow>>() → not available for DeferredWorld
• QueryState::<&Window>::new_from_world_cell() → works but requires unsafe
• Keeping the deprecated iter_entities() → works but noisy
• Moving all setup into a system with Added<Background> → safe but loses hook immediacy

I’d like to stay within the hook and keep things safe and modern—no unsafe or deprecated calls—if that’s possible.

---

Thoughts

Is this currently an oversight or intentional restriction of DeferredWorld?
If there’s a new recommended approach to “look up other components/resources” inside hooks in 0.17, I’d love to learn it.

---

Versions

• Bevy 0.17.2
• Rust 1.81.0
• Windows 10

[hymm]

you might be able to use try_query to construct a QueryState https://docs.rs/bevy/latest/bevy/ecs/world/struct.DeferredWorld.html#method.try_query

[mrknorman]

Thanks — this worked perfectly!

Using DeferredWorld::try_query let me safely replace my old iter_entities() call without any unsafe code or deprecation warnings.

Here’s what ended up working:

let Some(window) = world
    .try_query::<&Window>()                      // get a query for all Window components
    .and_then(|mut q| q.iter(&world).next())     // iterate and take the first one
    .cloned()                                    // clone so it can be used outside the borrow
else {
    warn!("No window found! Cannot spawn.");
    return;
};