pub struct Query<'world, 'state, D: QueryData, F: QueryFilter = ()> { /* private fields */ }
Expand description
System parameter that provides selective access to the Component
data stored in a World
.
Enables access to entity identifiers and components from a system, without the need to directly access the world. Its iterators and getter methods return query items. Each query item is a type containing data relative to an entity.
Query
is a generic data structure that accepts two type parameters:
D
(query data). The type of data contained in the query item. Only entities that match the requested data will generate an item. Must implement theQueryData
trait.F
(query filter). A set of conditions that determines whether query items should be kept or discarded. Must implement theQueryFilter
trait. This type parameter is optional.
§System parameter declaration
A query should always be declared as a system parameter.
This section shows the most common idioms involving the declaration of Query
.
§Component access
A query defined with a reference to a component as the query fetch type parameter can be used to generate items that refer to the data of said component.
// A component can be accessed by shared reference...
query: Query<&ComponentA>
// ... or by mutable reference.
query: Query<&mut ComponentA>
§Query filtering
Setting the query filter type parameter will ensure that each query item satisfies the given condition.
// Just `ComponentA` data will be accessed, but only for entities that also contain
// `ComponentB`.
query: Query<&ComponentA, With<ComponentB>>
§QueryData
or QueryFilter
tuples
Using tuples, each Query
type parameter can contain multiple elements.
In the following example, two components are accessed simultaneously, and the query items are filtered on two conditions.
query: Query<(&ComponentA, &ComponentB), (With<ComponentC>, Without<ComponentD>)>
§Entity identifier access
The identifier of an entity can be made available inside the query item by including Entity
in the query fetch type parameter.
query: Query<(Entity, &ComponentA)>
§Optional component access
A component can be made optional in a query by wrapping it into an Option
.
In this way, a query item can still be generated even if the queried entity does not contain the wrapped component.
In this case, its corresponding value will be None
.
// Generates items for entities that contain `ComponentA`, and optionally `ComponentB`.
query: Query<(&ComponentA, Option<&ComponentB>)>
See the documentation for AnyOf
to idiomatically declare many optional components.
See the performance section to learn more about the impact of optional components.
§Disjoint queries
A system cannot contain two queries that break Rust’s mutability rules.
In this case, the Without
filter can be used to disjoint them.
In the following example, two queries mutably access the same component.
Executing this system will panic, since an entity could potentially match the two queries at the same time by having both Player
and Enemy
components.
This would violate mutability rules.
fn randomize_health(
player_query: Query<&mut Health, With<Player>>,
enemy_query: Query<&mut Health, With<Enemy>>,
)
Adding a Without
filter will disjoint the queries.
In this way, any entity that has both Player
and Enemy
components is excluded from both queries.
fn randomize_health(
player_query: Query<&mut Health, (With<Player>, Without<Enemy>)>,
enemy_query: Query<&mut Health, (With<Enemy>, Without<Player>)>,
)
An alternative to this idiom is to wrap the conflicting queries into a ParamSet
.
§Whole Entity Access
EntityRef
s can be fetched from a query. This will give read-only access to any component on the entity,
and can be use to dynamically fetch any component without baking it into the query type. Due to this global
access to the entity, this will block any other system from parallelizing with it. As such these queries
should be sparingly used.
query: Query<(EntityRef, &ComponentA)>
As EntityRef
can read any component on an entity, a query using it will conflict with any mutable
access. It is strongly advised to couple EntityRef
queries with the use of either With
/Without
filters or ParamSets
. This also limits the scope of the query, which will improve iteration performance
and also allows it to parallelize with other non-conflicting systems.
// This will panic!
query: Query<(EntityRef, &mut ComponentA)>
// This will not panic.
query_a: Query<EntityRef, With<ComponentA>>,
query_b: Query<&mut ComponentB, Without<ComponentA>>,
§Accessing query items
The following table summarizes the behavior of the safe methods that can be used to get query items.
Query methods | Effect |
---|---|
iter [_mut ] | Returns an iterator over all query items. |
[iter().for_each() [iter_mut().for_each() ],par_iter [_mut ] | Runs a specified function for each query item. |
iter_many [_mut ] | Iterates or runs a specified function over query items generated by a list of entities. |
iter_combinations [_mut ] | Returns an iterator over all combinations of a specified number of query items. |
get [_mut ] | Returns the query item for the specified entity. |
many [_mut ],get_many [_mut ] | Returns the query items for the specified entities. |
single [_mut ],get_single [_mut ] | Returns the query item while verifying that there aren’t others. |
There are two methods for each type of query operation: immutable and mutable (ending with _mut
).
When using immutable methods, the query items returned are of type ROQueryItem
, a read-only version of the query item.
In this circumstance, every mutable reference in the query fetch type parameter is substituted by a shared reference.
§Performance
Creating a Query
is a low-cost constant operation.
Iterating it, on the other hand, fetches data from the world and generates items, which can have a significant computational cost.
Table
component storage type is much more optimized for query iteration than SparseSet
.
Two systems cannot be executed in parallel if both access the same component type where at least one of the accesses is mutable. This happens unless the executor can verify that no entity could be found in both queries.
Optional components increase the number of entities a query has to match against. This can hurt iteration performance, especially if the query solely consists of only optional components, since the query would iterate over each entity in the world.
The following table compares the computational complexity of the various methods and operations, where:
- n is the number of entities that match the query,
- r is the number of elements in a combination,
- k is the number of involved entities in the operation,
- a is the number of archetypes in the world,
- C is the binomial coefficient, used to count combinations. nCr is read as “n choose r” and is equivalent to the number of distinct unordered subsets of r elements that can be taken from a set of n elements.
Query operation | Computational complexity |
---|---|
iter [_mut ] | O(n) |
[iter().for_each() [iter_mut().for_each() ],par_iter [_mut ] | O(n) |
iter_many [_mut ] | O(k) |
iter_combinations [_mut ] | O(nCr) |
get [_mut ] | O(1) |
(get_ )many | O(k) |
(get_ )many_mut | O(k2) |
single [_mut ],get_single [_mut ] | O(a) |
Archetype based filtering (With , Without , Or ) | O(a) |
Change detection filtering (Added , Changed ) | O(a + n) |
§Iterator::for_each
for_each
methods are seen to be generally faster than directly iterating through iter
on worlds with high archetype
fragmentation, and may enable additional optimizations like autovectorization. It is strongly advised to only use
Iterator::for_each
if it tangibly improves performance. Always be sure profile or benchmark both before and
after the change!
// This might be result in better performance...
query.iter().for_each(|component| {
// do things with the component
});
// ...than this. Always be sure to benchmark to validate the difference!
for component in query.iter() {
// do things with the component
}
Implementations§
source§impl<'w, 's, D: QueryData, F: QueryFilter> Query<'w, 's, D, F>
impl<'w, 's, D: QueryData, F: QueryFilter> Query<'w, 's, D, F>
sourcepub fn to_readonly(&self) -> Query<'_, 's, D::ReadOnly, F>
pub fn to_readonly(&self) -> Query<'_, 's, D::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.
sourcepub fn iter(&self) -> QueryIter<'_, 's, D::ReadOnly, F> ⓘ
pub fn iter(&self) -> QueryIter<'_, 's, D::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.
sourcepub fn iter_mut(&mut self) -> QueryIter<'_, 's, D, F> ⓘ
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.
sourcepub fn iter_combinations<const K: usize>(
&self
) -> QueryCombinationIter<'_, 's, D::ReadOnly, F, K> ⓘ
pub fn iter_combinations<const K: usize>( &self ) -> QueryCombinationIter<'_, 's, D::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.
sourcepub fn iter_combinations_mut<const K: usize>(
&mut self
) -> QueryCombinationIter<'_, 's, D, F, K> ⓘ
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.
sourcepub fn iter_many<EntityList: IntoIterator>(
&self,
entities: EntityList
) -> QueryManyIter<'_, 's, D::ReadOnly, F, EntityList::IntoIter> ⓘ
pub fn iter_many<EntityList: IntoIterator>( &self, entities: EntityList ) -> QueryManyIter<'_, 's, D::ReadOnly, F, EntityList::IntoIter> ⓘ
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.
sourcepub fn iter_many_mut<EntityList: IntoIterator>(
&mut self,
entities: EntityList
) -> QueryManyIter<'_, 's, D, F, EntityList::IntoIter> ⓘ
pub fn iter_many_mut<EntityList: IntoIterator>( &mut self, entities: EntityList ) -> QueryManyIter<'_, 's, D, F, EntityList::IntoIter> ⓘ
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.
§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;
}
}
}
sourcepub unsafe fn iter_unsafe(&self) -> QueryIter<'_, 's, D, F> ⓘ
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
sourcepub unsafe fn iter_combinations_unsafe<const K: usize>(
&self
) -> QueryCombinationIter<'_, 's, D, F, K> ⓘ
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
anditer_combinations_mut
for the safe versions.
sourcepub unsafe fn iter_many_unsafe<EntityList: IntoIterator>(
&self,
entities: EntityList
) -> QueryManyIter<'_, 's, D, F, EntityList::IntoIter> ⓘ
pub unsafe fn iter_many_unsafe<EntityList: IntoIterator>( &self, entities: EntityList ) -> QueryManyIter<'_, 's, D, F, EntityList::IntoIter> ⓘ
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.
sourcepub fn par_iter(&self) -> QueryParIter<'_, '_, D::ReadOnly, F>
pub fn par_iter(&self) -> QueryParIter<'_, '_, D::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.
sourcepub fn par_iter_mut(&mut self) -> QueryParIter<'_, '_, D, F>
pub fn par_iter_mut(&mut self) -> QueryParIter<'_, '_, 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;
});
}
sourcepub fn get(
&self,
entity: Entity
) -> Result<ROQueryItem<'_, D>, QueryEntityError>
pub fn get( &self, entity: Entity ) -> Result<ROQueryItem<'_, D>, 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.
sourcepub fn get_many<const N: usize>(
&self,
entities: [Entity; N]
) -> Result<[ROQueryItem<'_, D>; N], QueryEntityError>
pub fn get_many<const N: usize>( &self, entities: [Entity; N] ) -> Result<[ROQueryItem<'_, D>; 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
.
§See also
get_many_mut
to get mutable query items.many
for the panicking version.
sourcepub fn many<const N: usize>(
&self,
entities: [Entity; N]
) -> [ROQueryItem<'_, D>; N]
pub fn many<const N: usize>( &self, entities: [Entity; N] ) -> [ROQueryItem<'_, D>; N]
Returns the read-only query items for the given array of Entity
.
§Panics
This method panics if there is a query mismatch or a non-existing entity.
§Examples
use bevy_ecs::prelude::*;
#[derive(Component)]
struct Targets([Entity; 3]);
#[derive(Component)]
struct Position{
x: i8,
y: i8
};
impl Position {
fn distance(&self, other: &Position) -> i8 {
// Manhattan distance is way easier to compute!
(self.x - other.x).abs() + (self.y - other.y).abs()
}
}
fn check_all_targets_in_range(targeting_query: Query<(Entity, &Targets, &Position)>, targets_query: Query<&Position>){
for (targeting_entity, targets, origin) in &targeting_query {
// We can use "destructuring" to unpack the results nicely
let [target_1, target_2, target_3] = targets_query.many(targets.0);
assert!(target_1.distance(origin) <= 5);
assert!(target_2.distance(origin) <= 5);
assert!(target_3.distance(origin) <= 5);
}
}
§See also
get_many
for the non-panicking version.
sourcepub fn get_mut(
&mut self,
entity: Entity
) -> Result<D::Item<'_>, QueryEntityError>
pub fn get_mut( &mut self, entity: Entity ) -> Result<D::Item<'_>, 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.
sourcepub fn get_many_mut<const N: usize>(
&mut self,
entities: [Entity; N]
) -> Result<[D::Item<'_>; N], QueryEntityError>
pub fn get_many_mut<const N: usize>( &mut self, entities: [Entity; N] ) -> Result<[D::Item<'_>; 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.
§See also
sourcepub fn many_mut<const N: usize>(
&mut self,
entities: [Entity; N]
) -> [D::Item<'_>; N]
pub fn many_mut<const N: usize>( &mut self, entities: [Entity; N] ) -> [D::Item<'_>; N]
Returns the query items for the given array of Entity
.
§Panics
This method panics if there is a query mismatch, a non-existing entity, or the same Entity
is included more than once in the array.
§Examples
use bevy_ecs::prelude::*;
#[derive(Component)]
struct Spring{
connected_entities: [Entity; 2],
strength: f32,
}
#[derive(Component)]
struct Position {
x: f32,
y: f32,
}
#[derive(Component)]
struct Force {
x: f32,
y: f32,
}
fn spring_forces(spring_query: Query<&Spring>, mut mass_query: Query<(&Position, &mut Force)>){
for spring in &spring_query {
// We can use "destructuring" to unpack our query items nicely
let [(position_1, mut force_1), (position_2, mut force_2)] = mass_query.many_mut(spring.connected_entities);
force_1.x += spring.strength * (position_1.x - position_2.x);
force_1.y += spring.strength * (position_1.y - position_2.y);
// Silence borrow-checker: I have split your mutable borrow!
force_2.x += spring.strength * (position_2.x - position_1.x);
force_2.y += spring.strength * (position_2.y - position_1.y);
}
}
§See also
get_many_mut
for the non panicking version.many
to get read-only query items.
sourcepub unsafe fn get_unchecked(
&self,
entity: Entity
) -> Result<D::Item<'_>, QueryEntityError>
pub unsafe fn get_unchecked( &self, entity: Entity ) -> Result<D::Item<'_>, 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.
sourcepub fn single(&self) -> ROQueryItem<'_, D>
pub fn single(&self) -> ROQueryItem<'_, D>
Returns a single read-only query item when there is exactly one entity matching the query.
§Panics
This method panics if the number of query items is not exactly one.
§Example
fn player_system(query: Query<&Position, With<Player>>) {
let player_position = query.single();
// do something with player_position
}
§See also
get_single
for the non-panicking version.single_mut
to get the mutable query item.
sourcepub fn get_single(&self) -> Result<ROQueryItem<'_, D>, QuerySingleError>
pub fn get_single(&self) -> Result<ROQueryItem<'_, D>, 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.get_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
get_single_mut
to get the mutable query item.single
for the panicking version.
sourcepub fn single_mut(&mut self) -> D::Item<'_>
pub fn single_mut(&mut self) -> D::Item<'_>
Returns a single query item when there is exactly one entity matching the query.
§Panics
This method panics if the number of query item is not exactly one.
§Example
fn regenerate_player_health_system(mut query: Query<&mut Health, With<Player>>) {
let mut health = query.single_mut();
health.0 += 1;
}
§See also
get_single_mut
for the non-panicking version.single
to get the read-only query item.
sourcepub fn get_single_mut(&mut self) -> Result<D::Item<'_>, QuerySingleError>
pub fn get_single_mut(&mut self) -> Result<D::Item<'_>, 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.get_single_mut().expect("Error: Could not find a single player.");
health.0 += 1;
}
§See also
get_single
to get the read-only query item.single_mut
for the panicking version.
sourcepub fn is_empty(&self) -> bool
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
or Changed
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;
}
}
sourcepub fn transmute_lens<NewD: QueryData>(&mut self) -> QueryLens<'_, NewD>
pub fn transmute_lens<NewD: QueryData>(&mut self) -> QueryLens<'_, NewD>
Returns a QueryLens
that can be used to get a query with a more general fetch.
For example, this can transform a Query<(&A, &mut B)>
to a Query<&B>
.
This can be useful for passing the query to another function. Note that since
filter terms are dropped, non-archetypal filters like Added
and
Changed
will not be respected. To maintain or change filter
terms see Self::transmute_lens_filtered
§Panics
This will panic if NewD
is not a subset of the original fetch Q
§Example
fn reusable_function(lens: &mut QueryLens<&A>) {
assert_eq!(lens.query().single().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);
}
§Allowed Transmutes
Besides removing parameters from the query, you can also make limited changes to the types of parameters.
- Can always add/remove
Entity
- Can always add/remove
EntityLocation
- Can always add/remove
&Archetype
Ref<T>
<->&T
&mut T
->&T
&mut T
->Ref<T>
EntityMut
->EntityRef
sourcepub fn transmute_lens_filtered<NewD: QueryData, NewF: QueryFilter>(
&mut self
) -> QueryLens<'_, NewD, NewF>
pub fn transmute_lens_filtered<NewD: QueryData, NewF: QueryFilter>( &mut self ) -> QueryLens<'_, NewD, NewF>
Equivalent to Self::transmute_lens
but also includes a QueryFilter
type.
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
and
Changed
will only be respected if they are in the type signature.
sourcepub fn as_query_lens(&mut self) -> QueryLens<'_, D>
pub fn as_query_lens(&mut self) -> QueryLens<'_, D>
Gets a QueryLens
with the same accesses as the existing query
sourcepub fn join<OtherD: QueryData, NewD: QueryData>(
&mut self,
other: &mut Query<'_, '_, OtherD>
) -> QueryLens<'_, NewD>
pub fn join<OtherD: QueryData, NewD: QueryData>( &mut self, other: &mut Query<'_, '_, OtherD> ) -> QueryLens<'_, NewD>
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
and Changed
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.
sourcepub fn join_filtered<OtherD: QueryData, OtherF: QueryFilter, NewD: QueryData, NewF: QueryFilter>(
&mut self,
other: &mut Query<'_, '_, OtherD, OtherF>
) -> QueryLens<'_, NewD, NewF>
pub fn join_filtered<OtherD: QueryData, OtherF: QueryFilter, NewD: QueryData, NewF: QueryFilter>( &mut self, other: &mut Query<'_, '_, OtherD, OtherF> ) -> QueryLens<'_, NewD, NewF>
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
and Changed
will only be respected if they are in
the type signature.
source§impl<'w, 's, D: ReadOnlyQueryData, F: QueryFilter> Query<'w, 's, D, F>
impl<'w, 's, D: ReadOnlyQueryData, F: QueryFilter> Query<'w, 's, D, F>
sourcepub fn get_inner(
&self,
entity: Entity
) -> Result<ROQueryItem<'w, D>, QueryEntityError>
pub fn get_inner( &self, entity: Entity ) -> Result<ROQueryItem<'w, D>, QueryEntityError>
Returns the query item for the given Entity
, with the actual “inner” world lifetime.
In case of a nonexisting entity or mismatched component, a QueryEntityError
is
returned instead.
This can only return immutable data (mutable data will be cast to an immutable form).
See get_mut
for queries that contain at least one mutable component.
§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);
}
}
sourcepub fn iter_inner(&self) -> QueryIter<'w, 's, D::ReadOnly, F> ⓘ
pub fn iter_inner(&self) -> QueryIter<'w, 's, D::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§
source§impl<'w, 's, D: QueryData + 'static, F: QueryFilter + 'static> BuildableSystemParam for Query<'w, 's, D, F>
impl<'w, 's, D: QueryData + 'static, F: QueryFilter + 'static> BuildableSystemParam for Query<'w, 's, D, F>
§type Builder<'b> = QueryBuilder<'b, D, F>
type Builder<'b> = QueryBuilder<'b, D, F>
source§fn build(
world: &mut World,
system_meta: &mut SystemMeta,
build: impl FnOnce(&mut Self::Builder<'_>)
) -> Self::State
fn build( world: &mut World, system_meta: &mut SystemMeta, build: impl FnOnce(&mut Self::Builder<'_>) ) -> Self::State
SystemParam::State
for Self
using a given builder functionsource§impl<'w, 'q, Q: QueryData, F: QueryFilter> From<&'q mut Query<'w, '_, Q, F>> for QueryLens<'q, Q, F>
impl<'w, 'q, Q: QueryData, F: QueryFilter> From<&'q mut Query<'w, '_, Q, F>> for QueryLens<'q, Q, F>
source§impl<'w, 's, Q: QueryData, F: QueryFilter> From<&'s mut QueryLens<'w, Q, F>> for Query<'w, 's, Q, F>
impl<'w, 's, Q: QueryData, F: QueryFilter> From<&'s mut QueryLens<'w, Q, F>> for Query<'w, 's, Q, F>
source§impl<'w, 's, D: QueryData, F: QueryFilter> IntoIterator for &'w Query<'_, 's, D, F>
impl<'w, 's, D: QueryData, F: QueryFilter> IntoIterator for &'w Query<'_, 's, D, F>
source§impl<'w, 's, D: QueryData, F: QueryFilter> IntoIterator for &'w mut Query<'_, 's, D, F>
impl<'w, 's, D: QueryData, F: QueryFilter> IntoIterator for &'w mut Query<'_, 's, D, F>
source§impl<D: QueryData + 'static, F: QueryFilter + 'static> SystemParam for Query<'_, '_, D, F>
impl<D: QueryData + 'static, F: QueryFilter + 'static> SystemParam for Query<'_, '_, D, F>
§type State = QueryState<D, F>
type State = QueryState<D, F>
§type Item<'w, 's> = Query<'w, 's, D, F>
type Item<'w, 's> = Query<'w, 's, D, F>
Self
, instantiated with new lifetimes. Read moresource§fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State
World
access used by this SystemParam
and creates a new instance of this param’s State
.source§unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta
)
unsafe fn new_archetype( state: &mut Self::State, archetype: &Archetype, system_meta: &mut SystemMeta )
Archetype
, registers the components accessed by this SystemParam
(if applicable).a Read moresource§unsafe fn get_param<'w, 's>(
state: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick
) -> Self::Item<'w, 's>
unsafe fn get_param<'w, 's>( state: &'s mut Self::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'w>, change_tick: Tick ) -> Self::Item<'w, 's>
SystemParamFunction
. Read moresource§fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World)
fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World)
SystemParam
’s state.
This is used to apply Commands
during apply_deferred
.source§fn queue(
state: &mut Self::State,
system_meta: &SystemMeta,
world: DeferredWorld<'_>
)
fn queue( state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld<'_> )
apply_deferred
.impl<'w, 's, D: ReadOnlyQueryData + 'static, F: QueryFilter + 'static> ReadOnlySystemParam for Query<'w, 's, D, F>
Auto Trait Implementations§
impl<'world, 'state, D, F> Freeze for Query<'world, 'state, D, F>
impl<'world, 'state, D, F = ()> !RefUnwindSafe for Query<'world, 'state, D, F>
impl<'world, 'state, D, F> Send for Query<'world, 'state, D, F>
impl<'world, 'state, D, F> Sync for Query<'world, 'state, D, F>
impl<'world, 'state, D, F> Unpin for Query<'world, 'state, D, F>
impl<'world, 'state, D, F = ()> !UnwindSafe for Query<'world, 'state, D, F>
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<T> Downcast for Twhere
T: Any,
impl<T> Downcast for Twhere
T: Any,
source§fn into_any(self: Box<T>) -> Box<dyn Any>
fn into_any(self: Box<T>) -> Box<dyn Any>
Box<dyn Trait>
(where Trait: Downcast
) to Box<dyn Any>
. Box<dyn Any>
can
then be further downcast
into Box<ConcreteType>
where ConcreteType
implements Trait
.source§fn into_any_rc(self: Rc<T>) -> Rc<dyn Any>
fn into_any_rc(self: Rc<T>) -> Rc<dyn Any>
Rc<Trait>
(where Trait: Downcast
) to Rc<Any>
. Rc<Any>
can then be
further downcast
into Rc<ConcreteType>
where ConcreteType
implements Trait
.source§fn as_any(&self) -> &(dyn Any + 'static)
fn as_any(&self) -> &(dyn Any + 'static)
&Trait
(where Trait: Downcast
) to &Any
. This is needed since Rust cannot
generate &Any
’s vtable from &Trait
’s.source§fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)
fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)
&mut Trait
(where Trait: Downcast
) to &Any
. This is needed since Rust cannot
generate &mut Any
’s vtable from &mut Trait
’s.