Struct Populated 

pub struct Populated<'w, 's, D, F = ()>(/* private fields */)
where
    D: QueryData,
    F: QueryFilter;

System parameter that works very much like Query except it always contains at least one matching entity.

This SystemParam fails validation if no matching entities exist. This will cause the system to be skipped, according to the rules laid out in SystemParamValidationError.

Much like Query::is_empty the worst case runtime will be O(n) where n is the number of potential matches. This can be notably expensive for queries that rely on non-archetypal filters such as Added, Changed of Spawned which must individually check each query result for a match.

See Query for more details.

Implementations

impl<'w, 's, D, F> Populated<'w, 's, D, F>

where D: QueryData, F: QueryFilter,

pub fn into_inner(self) -> Query<'w, 's, D, F>

Returns the inner item with ownership.

Methods from Deref<Target = Query<'w, 's, D, F>>

pub fn related<R>(&'w self, entity: Entity) -> Option<Entity>

where R: Relationship, <D as QueryData>::ReadOnly: QueryData<Item<'w, 's> = &'w R>,

If the given entity contains the R Relationship component, returns the target entity of that relationship.

pub fn relationship_sources<S>( &'w self, entity: Entity, ) -> impl Iterator<Item = Entity> + 'w

where S: RelationshipTarget, <D as QueryData>::ReadOnly: QueryData<Item<'w, 's> = &'w S>,

If the given entity contains the S RelationshipTarget component, returns the source entities stored on that component.

pub fn root_ancestor<R>(&'w self, entity: Entity) -> Entity

where R: Relationship, <D as QueryData>::ReadOnly: QueryData<Item<'w, 's> = &'w R>,

Recursively walks up the tree defined by the given R Relationship until there are no more related entities, returning the “root entity” of the relationship hierarchy.

Warning

For relationship graphs that contain loops, this could loop infinitely. If your relationship is not a tree (like Bevy’s hierarchy), be sure to stop if you encounter a duplicate entity.

pub fn iter_leaves<S>( &'w self, entity: Entity, ) -> impl Iterator<Item = Entity> + use<'w, 's, S, D, F>

where S: RelationshipTarget, <D as QueryData>::ReadOnly: QueryData<Item<'w, 's> = &'w S>, <<S as RelationshipTarget>::Collection as RelationshipSourceCollection>::SourceIter<'w>: DoubleEndedIterator,

Iterates all “leaf entities” as defined by the RelationshipTarget hierarchy.

Warning

For relationship graphs that contain loops, this could loop infinitely. If your relationship is not a tree (like Bevy’s hierarchy), be sure to stop if you encounter a duplicate entity.

pub fn iter_siblings<R>( &'w self, entity: Entity, ) -> impl Iterator<Item = Entity> + 'w

where R: Relationship, <D as QueryData>::ReadOnly: QueryData<Item<'w, 's> = (Option<&'w R>, Option<&'w <R as Relationship>::RelationshipTarget>)>,

Iterates all sibling entities that also have the R Relationship with the same target entity.

pub fn iter_descendants<S>( &'w self, entity: Entity, ) -> DescendantIter<'w, 's, D, F, S>

where S: RelationshipTarget, <D as QueryData>::ReadOnly: QueryData<Item<'w, 's> = &'w S>,

Iterates all descendant entities as defined by the given entity’s RelationshipTarget and their recursive RelationshipTarget.

Warning

For relationship graphs that contain loops, this could loop infinitely. If your relationship is not a tree (like Bevy’s hierarchy), be sure to stop if you encounter a duplicate entity.

pub fn iter_descendants_depth_first<S>( &'w self, entity: Entity, ) -> DescendantDepthFirstIter<'w, 's, D, F, S>

where S: RelationshipTarget, <D as QueryData>::ReadOnly: QueryData<Item<'w, 's> = &'w S>, <<S as RelationshipTarget>::Collection as RelationshipSourceCollection>::SourceIter<'w>: DoubleEndedIterator,

Iterates all descendant entities as defined by the given entity’s RelationshipTarget and their recursive RelationshipTarget in depth-first order.

Warning

For relationship graphs that contain loops, this could loop infinitely. If your relationship is not a tree (like Bevy’s hierarchy), be sure to stop if you encounter a duplicate entity.

pub fn iter_ancestors<R>( &'w self, entity: Entity, ) -> AncestorIter<'w, 's, D, F, R>

where R: Relationship, <D as QueryData>::ReadOnly: QueryData<Item<'w, 's> = &'w R>,

Iterates all ancestors of the given entity as defined by the R Relationship.

Warning

For relationship graphs that contain loops, this could loop infinitely. If your relationship is not a tree (like Bevy’s hierarchy), be sure to stop if you encounter a duplicate entity.

pub fn as_readonly(&self) -> Query<'_, 's, <D as QueryData>::ReadOnly, F>

Returns another Query from this that fetches the read-only version of the query items.

For example, Query<(&mut D1, &D2, &mut D3), With<F>> will become Query<(&D1, &D2, &D3), With<F>>. This can be useful when working around the borrow checker, or reusing functionality between systems via functions that accept query types.

See also

into_readonly for a version that consumes the Query to return one with the full 'world lifetime.

pub fn reborrow(&mut self) -> Query<'_, 's, D, F>

Returns a new Query reborrowing the access from this one. The current query will be unusable while the new one exists.

Example

For example this allows to call other methods or other systems that require an owned Query without completely giving up ownership of it.

fn helper_system(query: Query<&ComponentA>) { /* ... */}

fn system(mut query: Query<&ComponentA>) {
    helper_system(query.reborrow());
    // Can still use query here:
    for component in &query {
        // ...
    }
}

pub unsafe fn reborrow_unsafe(&self) -> Query<'_, 's, D, F>

Returns a new Query reborrowing the access from this one. The current query will still be usable while the new one exists, but must not be used in a way that violates aliasing.

Safety

This function makes it possible to violate Rust’s aliasing guarantees. You must make sure this call does not result in a mutable or shared reference to a component with a mutable reference.

See also

• reborrow for the safe versions.

pub fn iter(&self) -> QueryIter<'_, 's, <D as QueryData>::ReadOnly, F>

Returns an Iterator over the read-only query items.

This iterator is always guaranteed to return results from each matching entity once and only once. Iteration order is not guaranteed.

Example

Here, the report_names_system iterates over the Player component of every entity that contains it:

fn report_names_system(query: Query<&Player>) {
    for player in &query {
        println!("Say hello to {}!", player.name);
    }
}

See also

iter_mut for mutable query items.

pub fn iter_mut(&mut self) -> QueryIter<'_, 's, D, F>

Returns an Iterator over the query items.

This iterator is always guaranteed to return results from each matching entity once and only once. Iteration order is not guaranteed.

Example

Here, the gravity_system updates the Velocity component of every entity that contains it:

fn gravity_system(mut query: Query<&mut Velocity>) {
    const DELTA: f32 = 1.0 / 60.0;
    for mut velocity in &mut query {
        velocity.y -= 9.8 * DELTA;
    }
}

See also

iter for read-only query items.

pub fn iter_combinations<const K: usize>( &self, ) -> QueryCombinationIter<'_, 's, <D as QueryData>::ReadOnly, F, K>

Returns a QueryCombinationIter over all combinations of K read-only query items without repetition.

This iterator is always guaranteed to return results from each unique pair of matching entities. Iteration order is not guaranteed.

Example

fn some_system(query: Query<&ComponentA>) {
    for [a1, a2] in query.iter_combinations() {
        // ...
    }
}

See also

• iter_combinations_mut for mutable query item combinations.
• iter_combinations_inner for mutable query item combinations with the full 'world lifetime.

pub fn iter_combinations_mut<const K: usize>( &mut self, ) -> QueryCombinationIter<'_, 's, D, F, K>

Returns a QueryCombinationIter over all combinations of K query items without repetition.

This iterator is always guaranteed to return results from each unique pair of matching entities. Iteration order is not guaranteed.

Example

fn some_system(mut query: Query<&mut ComponentA>) {
    let mut combinations = query.iter_combinations_mut();
    while let Some([mut a1, mut a2]) = combinations.fetch_next() {
        // mutably access components data
    }
}

See also

• iter_combinations for read-only query item combinations.
• iter_combinations_inner for mutable query item combinations with the full 'world lifetime.

pub fn iter_many<EntityList>( &self, entities: EntityList, ) -> QueryManyIter<'_, 's, <D as QueryData>::ReadOnly, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: IntoIterator, <EntityList as IntoIterator>::Item: EntityEquivalent,

Returns an Iterator over the read-only query items generated from an Entity list.

Items are returned in the order of the list of entities, and may not be unique if the input doesn’t guarantee uniqueness. Entities that don’t match the query are skipped.

Example

// A component containing an entity list.
#[derive(Component)]
struct Friends {
    list: Vec<Entity>,
}

fn system(
    friends_query: Query<&Friends>,
    counter_query: Query<&Counter>,
) {
    for friends in &friends_query {
        for counter in counter_query.iter_many(&friends.list) {
            println!("Friend's counter: {}", counter.value);
        }
    }
}

See also

• iter_many_mut to get mutable query items.
• iter_many_inner to get mutable query items with the full 'world lifetime.

pub fn iter_many_mut<EntityList>( &mut self, entities: EntityList, ) -> QueryManyIter<'_, 's, D, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: IntoIterator, <EntityList as IntoIterator>::Item: EntityEquivalent,

Returns an iterator over the query items generated from an Entity list.

Items are returned in the order of the list of entities, and may not be unique if the input doesn’t guarantee uniqueness. Entities that don’t match the query are skipped.

Examples

#[derive(Component)]
struct Counter {
    value: i32
}

#[derive(Component)]
struct Friends {
    list: Vec<Entity>,
}

fn system(
    friends_query: Query<&Friends>,
    mut counter_query: Query<&mut Counter>,
) {
    for friends in &friends_query {
        let mut iter = counter_query.iter_many_mut(&friends.list);
        while let Some(mut counter) = iter.fetch_next() {
            println!("Friend's counter: {}", counter.value);
            counter.value += 1;
        }
    }
}

See also

• iter_many to get read-only query items.
• iter_many_inner to get mutable query items with the full 'world lifetime.

pub fn iter_many_unique<EntityList>( &self, entities: EntityList, ) -> QueryManyUniqueIter<'_, 's, <D as QueryData>::ReadOnly, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: EntitySet,

Returns an Iterator over the unique read-only query items generated from an EntitySet.

Items are returned in the order of the list of entities. Entities that don’t match the query are skipped.

Example

// `Friends` ensures that it only lists unique entities.
#[derive(Component)]
struct Friends {
    unique_list: Vec<Entity>,
}

impl<'a> IntoIterator for &'a Friends {

    type Item = &'a Entity;
    type IntoIter = UniqueEntityIter<slice::Iter<'a, Entity>>;

    fn into_iter(self) -> Self::IntoIter {
        // SAFETY: `Friends` ensures that it unique_list contains only unique entities.
       unsafe { UniqueEntityIter::from_iterator_unchecked(self.unique_list.iter()) }
    }
}

fn system(
    friends_query: Query<&Friends>,
    counter_query: Query<&Counter>,
) {
    for friends in &friends_query {
        for counter in counter_query.iter_many_unique(friends) {
            println!("Friend's counter: {:?}", counter.value);
        }
    }
}

See also

• iter_many_unique_mut to get mutable query items.
• iter_many_unique_inner to get with the actual “inner” world lifetime.

pub fn iter_many_unique_mut<EntityList>( &mut self, entities: EntityList, ) -> QueryManyUniqueIter<'_, 's, D, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: EntitySet,

Returns an iterator over the unique query items generated from an EntitySet.

Items are returned in the order of the list of entities. Entities that don’t match the query are skipped.

Examples

#[derive(Component)]
struct Counter {
    value: i32
}

// `Friends` ensures that it only lists unique entities.
#[derive(Component)]
struct Friends {
    unique_list: Vec<Entity>,
}

impl<'a> IntoIterator for &'a Friends {
    type Item = &'a Entity;
    type IntoIter = UniqueEntityIter<slice::Iter<'a, Entity>>;

    fn into_iter(self) -> Self::IntoIter {
        // SAFETY: `Friends` ensures that it unique_list contains only unique entities.
        unsafe { UniqueEntityIter::from_iterator_unchecked(self.unique_list.iter()) }
    }
}

fn system(
    friends_query: Query<&Friends>,
    mut counter_query: Query<&mut Counter>,
) {
    for friends in &friends_query {
        for mut counter in counter_query.iter_many_unique_mut(friends) {
            println!("Friend's counter: {:?}", counter.value);
            counter.value += 1;
        }
    }
}

See also

• iter_many_unique to get read-only query items.
• iter_many_unique_inner to get with the actual “inner” world lifetime.

pub unsafe fn iter_unsafe(&self) -> QueryIter<'_, 's, D, F>

Returns an Iterator over the query items.

This iterator is always guaranteed to return results from each matching entity once and only once. Iteration order is not guaranteed.

Safety

This function makes it possible to violate Rust’s aliasing guarantees. You must make sure this call does not result in multiple mutable references to the same component.

See also

• iter and iter_mut for the safe versions.

pub unsafe fn iter_combinations_unsafe<const K: usize>( &self, ) -> QueryCombinationIter<'_, 's, D, F, K>

Iterates over all possible combinations of K query items without repetition.

This iterator is always guaranteed to return results from each unique pair of matching entities. Iteration order is not guaranteed.

Safety

This allows aliased mutability. You must make sure this call does not result in multiple mutable references to the same component.

See also

• iter_combinations and iter_combinations_mut for the safe versions.

pub unsafe fn iter_many_unsafe<EntityList>( &self, entities: EntityList, ) -> QueryManyIter<'_, 's, D, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: IntoIterator, <EntityList as IntoIterator>::Item: EntityEquivalent,

Returns an Iterator over the query items generated from an Entity list.

Items are returned in the order of the list of entities, and may not be unique if the input doesnn’t guarantee uniqueness. Entities that don’t match the query are skipped.

Safety

This allows aliased mutability and does not check for entity uniqueness. You must make sure this call does not result in multiple mutable references to the same component. Particular care must be taken when collecting the data (rather than iterating over it one item at a time) such as via Iterator::collect.

See also

• iter_many_mut to safely access the query items.

pub unsafe fn iter_many_unique_unsafe<EntityList>( &self, entities: EntityList, ) -> QueryManyUniqueIter<'_, 's, D, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: EntitySet,

Returns an Iterator over the unique query items generated from an Entity list.

Items are returned in the order of the list of entities. Entities that don’t match the query are skipped.

Safety

This allows aliased mutability. You must make sure this call does not result in multiple mutable references to the same component.

See also

• iter_many_unique to get read-only query items.
• iter_many_unique_mut to get mutable query items.
• iter_many_unique_inner to get with the actual “inner” world lifetime.

pub fn par_iter(&self) -> QueryParIter<'_, 's, <D as QueryData>::ReadOnly, F>

Returns a parallel iterator over the query results for the given World.

This parallel iterator is always guaranteed to return results from each matching entity once and only once. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryIter.

This can only be called for read-only queries, see par_iter_mut for write-queries.

Note that you must use the for_each method to iterate over the results, see par_iter_mut for an example.

pub fn par_iter_mut(&mut self) -> QueryParIter<'_, 's, D, F>

Returns a parallel iterator over the query results for the given World.

This parallel iterator is always guaranteed to return results from each matching entity once and only once. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryIter.

This can only be called for mutable queries, see par_iter for read-only-queries.

Example

Here, the gravity_system updates the Velocity component of every entity that contains it:

fn gravity_system(mut query: Query<&mut Velocity>) {
    const DELTA: f32 = 1.0 / 60.0;
    query.par_iter_mut().for_each(|mut velocity| {
        velocity.y -= 9.8 * DELTA;
    });
}

pub fn par_iter_many<EntityList>( &self, entities: EntityList, ) -> QueryParManyIter<'_, 's, <D as QueryData>::ReadOnly, F, <EntityList as IntoIterator>::Item>

where EntityList: IntoIterator, <EntityList as IntoIterator>::Item: EntityEquivalent,

Returns a parallel iterator over the read-only query items generated from an Entity list.

Entities that don’t match the query are skipped. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryManyIter.

This can only be called for read-only queries. To avoid potential aliasing, there is no par_iter_many_mut equivalent. See par_iter_many_unique_mut for an alternative using EntitySet.

Note that you must use the for_each method to iterate over the results, see par_iter_mut for an example.

pub fn par_iter_many_unique<EntityList>( &self, entities: EntityList, ) -> QueryParManyUniqueIter<'_, 's, <D as QueryData>::ReadOnly, F, <EntityList as IntoIterator>::Item>

where EntityList: EntitySet, <EntityList as IntoIterator>::Item: Sync,

Returns a parallel iterator over the unique read-only query items generated from an EntitySet.

Entities that don’t match the query are skipped. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryManyUniqueIter.

This can only be called for read-only queries, see par_iter_many_unique_mut for write-queries.

Note that you must use the for_each method to iterate over the results, see par_iter_mut for an example.

pub fn par_iter_many_unique_mut<EntityList>( &mut self, entities: EntityList, ) -> QueryParManyUniqueIter<'_, 's, D, F, <EntityList as IntoIterator>::Item>

where EntityList: EntitySet, <EntityList as IntoIterator>::Item: Sync,

Returns a parallel iterator over the unique query items generated from an EntitySet.

Entities that don’t match the query are skipped. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryManyUniqueIter.

This can only be called for mutable queries, see par_iter_many_unique for read-only-queries.

Note that you must use the for_each method to iterate over the results, see par_iter_mut for an example.

pub fn get( &self, entity: Entity, ) -> Result<<<D as QueryData>::ReadOnly as QueryData>::Item<'_, 's>, QueryEntityError>

Returns the read-only query item for the given Entity.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This is always guaranteed to run in O(1) time.

Example

Here, get is used to retrieve the exact query item of the entity specified by the SelectedCharacter resource.

fn print_selected_character_name_system(
       query: Query<&Character>,
       selection: Res<SelectedCharacter>
)
{
    if let Ok(selected_character) = query.get(selection.entity) {
        println!("{}", selected_character.name);
    }
}

See also

• get_mut to get a mutable query item.

pub fn get_many<const N: usize>( &self, entities: [Entity; N], ) -> Result<[<<D as QueryData>::ReadOnly as QueryData>::Item<'_, 's>; N], QueryEntityError>

Returns the read-only query items for the given array of Entity.

The returned query items are in the same order as the input. In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead. The elements of the array do not need to be unique, unlike get_many_mut.

Examples

use bevy_ecs::prelude::*;
use bevy_ecs::query::QueryEntityError;

#[derive(Component, PartialEq, Debug)]
struct A(usize);

let mut world = World::new();
let entity_vec: Vec<Entity> = (0..3).map(|i| world.spawn(A(i)).id()).collect();
let entities: [Entity; 3] = entity_vec.try_into().unwrap();

world.spawn(A(73));

let mut query_state = world.query::<&A>();
let query = query_state.query(&world);

let component_values = query.get_many(entities).unwrap();

assert_eq!(component_values, [&A(0), &A(1), &A(2)]);

let wrong_entity = Entity::from_raw_u32(365).unwrap();

assert_eq!(
    match query.get_many([wrong_entity]).unwrap_err() {
        QueryEntityError::EntityDoesNotExist(error) => error.entity,
        _ => panic!(),
    },
    wrong_entity
);

See also

• get_many_mut to get mutable query items.
• get_many_unique to only handle unique inputs.

pub fn get_many_unique<const N: usize>( &self, entities: UniqueEntityEquivalentArray<Entity, N>, ) -> Result<[<<D as QueryData>::ReadOnly as QueryData>::Item<'_, 's>; N], QueryEntityError>

Returns the read-only query items for the given UniqueEntityArray.

The returned query items are in the same order as the input. In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

Examples

use bevy_ecs::{prelude::*, query::QueryEntityError, entity::{EntitySetIterator, UniqueEntityArray, UniqueEntityVec}};

#[derive(Component, PartialEq, Debug)]
struct A(usize);

let mut world = World::new();
let entity_set: UniqueEntityVec = world.spawn_batch((0..3).map(A)).collect_set();
let entity_set: UniqueEntityArray<3> = entity_set.try_into().unwrap();

world.spawn(A(73));

let mut query_state = world.query::<&A>();
let query = query_state.query(&world);

let component_values = query.get_many_unique(entity_set).unwrap();

assert_eq!(component_values, [&A(0), &A(1), &A(2)]);

let wrong_entity = Entity::from_raw_u32(365).unwrap();

assert_eq!(
    match query.get_many_unique(UniqueEntityArray::from([wrong_entity])).unwrap_err() {
        QueryEntityError::EntityDoesNotExist(error) => error.entity,
        _ => panic!(),
    },
    wrong_entity
);

See also

• get_many_unique_mut to get mutable query items.
• get_many to handle inputs with duplicates.

pub fn get_mut( &mut self, entity: Entity, ) -> Result<<D as QueryData>::Item<'_, 's>, QueryEntityError>

Returns the query item for the given Entity.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This is always guaranteed to run in O(1) time.

Example

Here, get_mut is used to retrieve the exact query item of the entity specified by the PoisonedCharacter resource.

fn poison_system(mut query: Query<&mut Health>, poisoned: Res<PoisonedCharacter>) {
    if let Ok(mut health) = query.get_mut(poisoned.character_id) {
        health.0 -= 1;
    }
}

See also

• get to get a read-only query item.

pub fn get_many_mut<const N: usize>( &mut self, entities: [Entity; N], ) -> Result<[<D as QueryData>::Item<'_, 's>; N], QueryEntityError>

Returns the query items for the given array of Entity.

The returned query items are in the same order as the input. In case of a nonexisting entity, duplicate entities or mismatched component, a QueryEntityError is returned instead.

Examples

use bevy_ecs::prelude::*;
use bevy_ecs::query::QueryEntityError;

#[derive(Component, PartialEq, Debug)]
struct A(usize);

let mut world = World::new();

let entities: Vec<Entity> = (0..3).map(|i| world.spawn(A(i)).id()).collect();
let entities: [Entity; 3] = entities.try_into().unwrap();

world.spawn(A(73));
let wrong_entity = Entity::from_raw_u32(57).unwrap();
let invalid_entity = world.spawn_empty().id();


let mut query_state = world.query::<&mut A>();
let mut query = query_state.query_mut(&mut world);

let mut mutable_component_values = query.get_many_mut(entities).unwrap();

for mut a in &mut mutable_component_values {
    a.0 += 5;
}

let component_values = query.get_many(entities).unwrap();

assert_eq!(component_values, [&A(5), &A(6), &A(7)]);

assert_eq!(
    match query
        .get_many_mut([wrong_entity])
        .unwrap_err()
    {
        QueryEntityError::EntityDoesNotExist(error) => error.entity,
        _ => panic!(),
    },
    wrong_entity
);
assert_eq!(
    match query
        .get_many_mut([invalid_entity])
        .unwrap_err()
    {
        QueryEntityError::QueryDoesNotMatch(entity, _) => entity,
        _ => panic!(),
    },
    invalid_entity
);
assert_eq!(
    query
        .get_many_mut([entities[0], entities[0]])
        .unwrap_err(),
    QueryEntityError::AliasedMutability(entities[0])
);

See also

• get_many to get read-only query items without checking for duplicate entities.

pub fn get_many_unique_mut<const N: usize>( &mut self, entities: UniqueEntityEquivalentArray<Entity, N>, ) -> Result<[<D as QueryData>::Item<'_, 's>; N], QueryEntityError>

Returns the query items for the given UniqueEntityArray.

The returned query items are in the same order as the input. In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

Examples

use bevy_ecs::{prelude::*, query::QueryEntityError, entity::{EntitySetIterator, UniqueEntityArray, UniqueEntityVec}};

#[derive(Component, PartialEq, Debug)]
struct A(usize);

let mut world = World::new();

let entity_set: UniqueEntityVec = world.spawn_batch((0..3).map(A)).collect_set();
let entity_set: UniqueEntityArray<3> = entity_set.try_into().unwrap();

world.spawn(A(73));
let wrong_entity = Entity::from_raw_u32(57).unwrap();
let invalid_entity = world.spawn_empty().id();


let mut query_state = world.query::<&mut A>();
let mut query = query_state.query_mut(&mut world);

let mut mutable_component_values = query.get_many_unique_mut(entity_set).unwrap();

for mut a in &mut mutable_component_values {
    a.0 += 5;
}

let component_values = query.get_many_unique(entity_set).unwrap();

assert_eq!(component_values, [&A(5), &A(6), &A(7)]);

assert_eq!(
    match query
        .get_many_unique_mut(UniqueEntityArray::from([wrong_entity]))
        .unwrap_err()
    {
        QueryEntityError::EntityDoesNotExist(error) => error.entity,
        _ => panic!(),
    },
    wrong_entity
);
assert_eq!(
    match query
        .get_many_unique_mut(UniqueEntityArray::from([invalid_entity]))
        .unwrap_err()
    {
        QueryEntityError::QueryDoesNotMatch(entity, _) => entity,
        _ => panic!(),
    },
    invalid_entity
);

See also

• get_many_unique to get read-only query items.

pub unsafe fn get_unchecked( &self, entity: Entity, ) -> Result<<D as QueryData>::Item<'_, 's>, QueryEntityError>

Returns the query item for the given Entity.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This is always guaranteed to run in O(1) time.

Safety

This function makes it possible to violate Rust’s aliasing guarantees. You must make sure this call does not result in multiple mutable references to the same component.

See also

• get_mut for the safe version.

pub fn single( &self, ) -> Result<<<D as QueryData>::ReadOnly as QueryData>::Item<'_, 's>, QuerySingleError>

Returns a single read-only query item when there is exactly one entity matching the query.

If the number of query items is not exactly one, a QuerySingleError is returned instead.

Example

fn player_scoring_system(query: Query<&PlayerScore>) {
    match query.single() {
        Ok(PlayerScore(score)) => {
            println!("Score: {}", score);
        }
        Err(QuerySingleError::NoEntities(_)) => {
            println!("Error: There is no player!");
        }
        Err(QuerySingleError::MultipleEntities(_)) => {
            println!("Error: There is more than one player!");
        }
    }
}

See also

• single_mut to get the mutable query item.

pub fn single_mut( &mut self, ) -> Result<<D as QueryData>::Item<'_, 's>, QuerySingleError>

Returns a single query item when there is exactly one entity matching the query.

If the number of query items is not exactly one, a QuerySingleError is returned instead.

Example

fn regenerate_player_health_system(mut query: Query<&mut Health, With<Player>>) {
    let mut health = query.single_mut().expect("Error: Could not find a single player.");
    health.0 += 1;
}

See also

• single to get the read-only query item.

pub fn is_empty(&self) -> bool

Returns true if there are no query items.

This is equivalent to self.iter().next().is_none(), and thus the worst case runtime will be O(n) where n is the number of potential matches. This can be notably expensive for queries that rely on non-archetypal filters such as Added, Changed or Spawned which must individually check each query result for a match.

Example

Here, the score is increased only if an entity with a Player component is present in the world:

fn update_score_system(query: Query<(), With<Player>>, mut score: ResMut<Score>) {
    if !query.is_empty() {
        score.0 += 1;
    }
}

pub fn contains(&self, entity: Entity) -> bool

Returns true if the given Entity matches the query.

This is always guaranteed to run in O(1) time.

Example

fn targeting_system(in_range_query: Query<&InRange>, target: Res<Target>) {
    if in_range_query.contains(target.entity) {
        println!("Bam!")
    }
}

pub fn count(&self) -> usize

Counts the number of entities that match the query.

This is equivalent to self.iter().count() but may be more efficient in some cases.

If F::IS_ARCHETYPAL is true, this will do work proportional to the number of matched archetypes or tables, but will not iterate each entity. If it is false, it will have to do work for each entity.

Example

fn targeting_system(in_range_query: Query<&InRange>) {
    let count = in_range_query.count();
    println!("{count} targets in range!");
}

pub fn transmute_lens<NewD>(&mut self) -> QueryLens<'_, NewD>

where NewD: QueryData,

Returns a QueryLens that can be used to construct a new Query giving more restrictive access to the entities matched by the current query.

A transmute is valid only if NewD has a subset of the read, write, and required access of the current query. A precise description of the access required by each parameter type is given in the table below, but typical uses are to:

• Remove components, e.g. Query<(&A, &B)> to Query<&A>.
• Retrieve an existing component with reduced or equal access, e.g. Query<&mut A> to Query<&A> or Query<&T> to Query<Ref<T>>.
• Add parameters with no new access, for example adding an Entity parameter.

Note that since filter terms are dropped, non-archetypal filters like Added, Changed and Spawned will not be respected. To maintain or change filter terms see Self::transmute_lens_filtered.

QueryData parameter type	Access required
Entity, EntityLocation, SpawnDetails, &Archetype, Has<T>, PhantomData<T>	No access
EntityMut	Read and write access to all components, but no required access
EntityRef	Read access to all components, but no required access
&T, Ref<T>	Read and required access to T
&mut T, Mut<T>	Read, write and required access to T
Option<T>, AnyOf<(D, ...)>	Read and write access to T, but no required access
Tuples of query data and #[derive(QueryData)] structs	The union of the access of their subqueries
FilteredEntityRef, FilteredEntityMut	Determined by the QueryBuilder used to construct them. Any query can be transmuted to them, and they will receive the access of the source query. When combined with other QueryData, they will receive any access of the source query that does not conflict with the other data

transmute_lens drops filter terms, but Self::transmute_lens_filtered supports returning a QueryLens with a new filter type - the access required by filter parameters are as follows.

QueryFilter parameter type	Access required
Added<T>, Changed<T>	Read and required access to T
With<T>, Without<T>	No access
Or<(T, ...)>	Read access of the subqueries, but no required access
Tuples of query filters and #[derive(QueryFilter)] structs	The union of the access of their subqueries

Panics

This will panic if the access required by NewD is not a subset of that required by the original fetch D.

Example

fn reusable_function(lens: &mut QueryLens<&A>) {
    assert_eq!(lens.query().single().unwrap().0, 10);
}

// We can use the function in a system that takes the exact query.
fn system_1(mut query: Query<&A>) {
    reusable_function(&mut query.as_query_lens());
}

// We can also use it with a query that does not match exactly
// by transmuting it.
fn system_2(mut query: Query<(&mut A, &B)>) {
    let mut lens = query.transmute_lens::<&A>();
    reusable_function(&mut lens);
}

Examples of valid transmutes

// `&mut T` and `Mut<T>` access the same data and can be transmuted to each other,
// `&T` and `Ref<T>` access the same data and can be transmuted to each other,
// and mutable versions can be transmuted to read-only versions
assert_valid_transmute::<&mut T, &T>();
assert_valid_transmute::<&mut T, Mut<T>>();
assert_valid_transmute::<Mut<T>, &mut T>();
assert_valid_transmute::<&T, Ref<T>>();
assert_valid_transmute::<Ref<T>, &T>();

// The structure can be rearranged, or subqueries dropped
assert_valid_transmute::<(&T, &U), &T>();
assert_valid_transmute::<((&T, &U), &V), (&T, (&U, &V))>();
assert_valid_transmute::<Option<(&T, &U)>, (Option<&T>, Option<&U>)>();

// Queries with no access can be freely added
assert_valid_transmute::<
    &T,
    (&T, Entity, EntityLocation, &Archetype, Has<U>, PhantomData<T>),
>();

// Required access can be transmuted to optional,
// and optional access can be transmuted to other optional access
assert_valid_transmute::<&T, Option<&T>>();
assert_valid_transmute::<AnyOf<(&mut T, &mut U)>, Option<&T>>();
// Note that removing subqueries from `AnyOf` will result
// in an `AnyOf` where all subqueries can yield `None`!
assert_valid_transmute::<AnyOf<(&T, &U, &V)>, AnyOf<(&T, &U)>>();
assert_valid_transmute::<EntityMut, Option<&mut T>>();

// Anything can be transmuted to `FilteredEntityRef` or `FilteredEntityMut`
// This will create a `FilteredEntityMut` that only has read access to `T`
assert_valid_transmute::<&T, FilteredEntityMut>();
// This will create a `FilteredEntityMut` that has no access to `T`,
// read access to `U`, and write access to `V`.
assert_valid_transmute::<(&mut T, &mut U, &mut V), (&mut T, &U, FilteredEntityMut)>();

// `Added<T>` and `Changed<T>` filters have the same access as `&T` data
// Remember that they are only evaluated on the transmuted query, not the original query!
assert_valid_transmute_filtered::<Entity, Changed<T>, &T, ()>();
assert_valid_transmute_filtered::<&mut T, (), &T, Added<T>>();
// Nested inside of an `Or` filter, they have the same access as `Option<&T>`.
assert_valid_transmute_filtered::<Option<&T>, (), Entity, Or<(Changed<T>, With<U>)>>();

pub fn transmute_lens_filtered<NewD, NewF>( &mut self, ) -> QueryLens<'_, NewD, NewF>

where NewD: QueryData, NewF: QueryFilter,

Equivalent to Self::transmute_lens but also includes a QueryFilter type.

See Self::transmute_lens for a description of allowed transmutes.

Note that the lens will iterate the same tables and archetypes as the original query. This means that additional archetypal query terms like With and Without will not necessarily be respected and non-archetypal terms like Added, Changed and Spawned will only be respected if they are in the type signature.

pub fn as_query_lens(&mut self) -> QueryLens<'_, D>

Gets a QueryLens with the same accesses as the existing query

pub fn join<'a, OtherD, NewD>( &'a mut self, other: &'a mut Query<'_, '_, OtherD>, ) -> QueryLens<'a, NewD>

where OtherD: QueryData, NewD: QueryData,

Returns a QueryLens that can be used to get a query with the combined fetch.

For example, this can take a Query<&A> and a Query<&B> and return a Query<(&A, &B)>. The returned query will only return items with both A and B. Note that since filters are dropped, non-archetypal filters like Added, Changed and Spawned will not be respected. To maintain or change filter terms see Self::join_filtered.

Example

fn system(
    mut transforms: Query<&Transform>,
    mut players: Query<&Player>,
    mut enemies: Query<&Enemy>
) {
    let mut players_transforms: QueryLens<(&Transform, &Player)> = transforms.join(&mut players);
    for (transform, player) in &players_transforms.query() {
        // do something with a and b
    }

    let mut enemies_transforms: QueryLens<(&Transform, &Enemy)> = transforms.join(&mut enemies);
    for (transform, enemy) in &enemies_transforms.query() {
        // do something with a and b
    }
}

Panics

This will panic if NewD is not a subset of the union of the original fetch Q and OtherD.

Allowed Transmutes

Like transmute_lens the query terms can be changed with some restrictions. See Self::transmute_lens for more details.

pub fn join_filtered<'a, OtherD, OtherF, NewD, NewF>( &'a mut self, other: &'a mut Query<'_, '_, OtherD, OtherF>, ) -> QueryLens<'a, NewD, NewF>

where OtherD: QueryData, OtherF: QueryFilter, NewD: QueryData, NewF: QueryFilter,

Equivalent to Self::join but also includes a QueryFilter type.

Note that the lens with iterate a subset of the original queries’ tables and archetypes. This means that additional archetypal query terms like With and Without will not necessarily be respected and non-archetypal terms like Added, Changed and Spawned will only be respected if they are in the type signature.

pub fn iter_inner(&self) -> QueryIter<'w, 's, <D as QueryData>::ReadOnly, F>

Returns an Iterator over the query items, with the actual “inner” world lifetime.

This can only return immutable data (mutable data will be cast to an immutable form). See Self::iter_mut for queries that contain at least one mutable component.

Example

Here, the report_names_system iterates over the Player component of every entity that contains it:

fn report_names_system(query: Query<&Player>) {
    for player in &query {
        println!("Say hello to {}!", player.name);
    }
}

Trait Implementations

impl<'w, 's, D, F> Deref for Populated<'w, 's, D, F>

where D: QueryData, F: QueryFilter,

type Target = Query<'w, 's, D, F>

The resulting type after dereferencing.

fn deref(&self) -> &<Populated<'w, 's, D, F> as Deref>::Target

Dereferences the value.

impl<D, F> DerefMut for Populated<'_, '_, D, F>

where D: QueryData, F: QueryFilter,

fn deref_mut(&mut self) -> &mut <Populated<'_, '_, D, F> as Deref>::Target

Mutably dereferences the value.

impl<'a, 'w, 's, D, F> IntoIterator for &'a Populated<'w, 's, D, F>

where D: QueryData, F: QueryFilter,

type Item = <&'a Query<'w, 's, D, F> as IntoIterator>::Item

The type of the elements being iterated over.

type IntoIter = <&'a Query<'w, 's, D, F> as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?

fn into_iter(self) -> <&'a Populated<'w, 's, D, F> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<'a, 'w, 's, D, F> IntoIterator for &'a mut Populated<'w, 's, D, F>

where D: QueryData, F: QueryFilter,

type Item = <&'a mut Query<'w, 's, D, F> as IntoIterator>::Item

The type of the elements being iterated over.

type IntoIter = <&'a mut Query<'w, 's, D, F> as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?

fn into_iter( self, ) -> <&'a mut Populated<'w, 's, D, F> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<'w, 's, D, F> IntoIterator for Populated<'w, 's, D, F>

where D: QueryData, F: QueryFilter,

type Item = <Query<'w, 's, D, F> as IntoIterator>::Item

The type of the elements being iterated over.

type IntoIter = <Query<'w, 's, D, F> as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?

fn into_iter(self) -> <Populated<'w, 's, D, F> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<D, F> SystemParam for Populated<'_, '_, D, F>

where D: QueryData + 'static, F: QueryFilter + 'static,

type State = QueryState<D, F>

Used to store data which persists across invocations of a system.

type Item<'w, 's> = Populated<'w, 's, D, F>

The item type returned when constructing this system param. The value of this associated type should be Self, instantiated with new lifetimes.

fn init_state( world: &mut World, ) -> <Populated<'_, '_, D, F> as SystemParam>::State

Creates a new instance of this param’s State.

fn init_access( state: &<Populated<'_, '_, D, F> as SystemParam>::State, system_meta: &mut SystemMeta, component_access_set: &mut FilteredAccessSet, world: &mut World, )

Registers any World access used by this SystemParam

unsafe fn get_param<'w, 's>( state: &'s mut <Populated<'_, '_, D, F> as SystemParam>::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'w>, change_tick: Tick, ) -> <Populated<'_, '_, D, F> as SystemParam>::Item<'w, 's>

Creates a parameter to be passed into a SystemParamFunction.

unsafe fn validate_param( state: &mut <Populated<'_, '_, D, F> as SystemParam>::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'_>, ) -> Result<(), SystemParamValidationError>

Validates that the param can be acquired by the get_param.

fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World)

Applies any deferred mutations stored in this SystemParam’s state. This is used to apply Commands during ApplyDeferred.

fn queue( state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld<'_>, )

Queues any deferred mutations to be applied at the next ApplyDeferred.

impl<'w, 's, D, F> ReadOnlySystemParam for Populated<'w, 's, D, F>

where D: ReadOnlyQueryData + 'static, F: QueryFilter + 'static,