Executing a system once during runtime from another system

[AndreasHGK]

I am currently working on a simple prototype to experiment with Bevy
So far I am really enjoying how simple everything is, even tho this is my first rust project ever Bevy makes it pretty intuitive

However I am unsure how to do the following:
I want to make it so when I presses O on their keyboard it will spawn a dummy player (for testing).
I have this system to listen to keypressed:

pub fn debug_spawn(input: Res<Input<KeyCode>>) {
    if input.just_pressed(KeyCode::O) {
        // somehow execute spawn_dummy
    }
}

And the following system to spawn a dummy player:

pub fn spawn_dummy(mut commands: Commands, materials: Res<Materials>, mut c_mat: ResMut<Assets<ColorMaterial>>) {
    let mut mat = materials.player_material.clone();
    c_mat.get_mut(&mat).unwrap().color = AlignmentColors::Enemy.into();

    let sprite = SpriteBundle {
        material: mat,
        ..Default::default()
    };

    commands.spawn_bundle(sprite).insert_bundle(PlayerBundle {
        ..Default::default()
    });
}

How can I make the spawn_dummy system run from the debug_spawn system? Do I just add mut commands: Commands, materials: Res<Materials>, mut c_mat: ResMut<Assets<ColorMaterial>> as parameters to debug_spawn and call spawn_dummy manually, or is there a better way to do this?

[hymm]

you're probably looking for events https://bevy-cheatbook.github.io/programming/events.html

[AndreasHGK]

Thanks, I'll take a look!

[djeedai]

Note that if you're sure you want that to happen only once it's probably better to call spawn_dummy() directly, to avoid leaving registered a system (see #3131). But here if you do it each time a key is pressed, this is not "once" but "once in a while", and events are indeed better suited for that kind of thing, to decouple a bit the two systems.

[tatref]

As of 0.12, you probably want One-Shot Systems