examples/queries/
query_variables.rs

1use crate::z_ignore_test_common::*;
2
3use flecs_ecs::prelude::*;
4
5#[derive(Component)]
6pub struct Eats;
7
8#[derive(Component)]
9struct Healthy;
10
11fn main() {
12    let world = World::new();
13
14    let apples = world.entity_named("Apples").add(Healthy);
15    let salad = world.entity_named("Salad").add(Healthy);
16    let burgers = world.entity_named("Burgers");
17    let pizza = world.entity_named("Pizza");
18    let chocolate = world.entity_named("Chocolate");
19
20    world
21        .entity_named("Bob")
22        .add((Eats, apples))
23        .add((Eats, burgers))
24        .add((Eats, pizza));
25
26    world
27        .entity_named("Alice")
28        .add((Eats, salad))
29        .add((Eats, chocolate))
30        .add((Eats, apples));
31
32    // Here we're creating a rule that in the query DSL would look like this:
33    //   Eats($This, $Food), Healthy($Food)
34    //
35    // example shows how the basics of how to use queries & variables.
36
37    let rule = world
38        .query::<()>()
39        // Identifiers that start with _ are query variables. Query variables
40        // are like wildcards, but enforce that the entity substituted by the
41        // wildcard is the same across terms.
42        //
43        // For example, in this query it is not guaranteed that the entity
44        // substituted by the * for Eats is the same as for Healthy:
45        //   (Eats, *), Healthy(*)
46        //
47        // By replacing * with _Food, both terms are constrained to use the
48        // same entity.
49        .with((Eats, "$food"))
50        .with(&Healthy)
51        .set_src("$food")
52        .build();
53
54    // Lookup the index of the variable. This will let us quickly lookup its
55    // value while we're iterating.
56    let food_var = rule.find_var("food");
57
58    // Iterate the rule
59    rule.each_iter(|it, index, ()| {
60        println!(
61            "{} eats {}",
62            it.entity(index).name(),
63            it.get_var(food_var.unwrap()).name()
64        );
65    });
66
67    // Output:
68    // Bob eats Apples
69    // Alice eats Apples
70    // Alice eats Salad
71}
72
73#[cfg(feature = "flecs_nightly_tests")]
74#[test]
75fn test() {
76    let output_capture = OutputCapture::capture().unwrap();
77    main();
78    output_capture.test("query_variables".to_string());
79}
examples/queries/query_variables.rs

examples/queries/
query_variables.rs
