How to run a query on a DeferredWorld ?

[gwafotapa]

I would like to run a query on a DeferredWorld in an on-add hook but I'm getting the error that the world cannot be borrowed as mutable. I understand the problem but I don't see how to get around it because:

1. The query() method of DeferredWorld needs a QueryState parameter
2. The two ways to build a QueryState (new() or from a QueryBuilder) both require a mutable world.
   So I'm stuck. Is this normal (meaning that query() isn't supposed to be called in a hook) or is there a way to run the query ?

[alice-i-cecile]

It seems quite odd and unhelpful to me that DeferredWorld::query has that API. The Deref<Target=World> doesn't help us either, because of the need for &mut World to initialize queries. https://dev-docs.bevyengine.org/bevy/ecs/world/struct.World.html#method.try_query will help though!

See #16923 though!

[hymm]

You need to construct the QueryState ahead of time and store it in the world as a resource or a component.

[gwafotapa]

@alice-i-cecile That would solve my problem except I can't find that try_query method. The page you linked says 0.16-dev while I'm using the 0.15.1 version of Bevy which is the latest. I'm confused.

@hymm That should work. That feels pretty inelegant though.

[gwafotapa]

@alice-i-cecile Sorry I should have read #16923 that you pointed out first. It cleared things up.