# B0001 To keep [Rust rules on references](https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html#the-rules-of-references) (either one mutable reference or any number of immutable references) on a component, it is not possible to have two queries on the same component when one requests mutable access to it in the same system. Erroneous code example: ```rust,should_panic use bevy::prelude::*; #[derive(Component)] struct Player; #[derive(Component)] struct Enemy; fn move_enemies_to_player( mut enemies: Query<&mut Transform, With<Enemy>>, player: Query<&Transform, With<Player>>, ) { // ... } fn main() { App::new() .add_plugins(DefaultPlugins) .add_systems(Update, move_enemies_to_player) .run(); } ``` This will panic, as it's not possible to have both a mutable and an immutable query on `Transform` at the same time. You have two solutions: Solution #1: use disjoint queries using [`Without`](https://docs.rs/bevy/*/bevy/ecs/query/struct.Without.html) As a `Player` entity won't be an `Enemy` at the same time, those two queries will actually never target the same entity. This can be encoded in the query filter with [`Without`](https://docs.rs/bevy/*/bevy/ecs/query/struct.Without.html): ```rust,no_run use bevy::prelude::*; #[derive(Component)] struct Player; #[derive(Component)] struct Enemy; fn move_enemies_to_player( mut enemies: Query<&mut Transform, With<Enemy>>, player: Query<&Transform, (With<Player>, Without<Enemy>)>, ) { // ... } fn main() { App::new() .add_plugins(DefaultPlugins) .add_systems(Update, move_enemies_to_player) .run(); } ``` Solution #2: use a `ParamSet` A `ParamSet` will let you have conflicting queries as a parameter, but you will still be responsible for not using them at the same time in your system. ```rust,no_run use bevy::prelude::*; #[derive(Component)] struct Player; #[derive(Component)] struct Enemy; fn move_enemies_to_player( mut transforms: ParamSet<( Query<&mut Transform, With<Enemy>>, Query<&Transform, With<Player>>, )>, ) { // ... } fn main() { App::new() .add_plugins(DefaultPlugins) .add_systems(Update, move_enemies_to_player) .run(); } ```