QueryPredicate

An object that defines the criteria for an entity query.

Declaration

struct QueryPredicate<Value>

Mentioned in

Implementing systems for entities in a scene

Overview

Query predicates specify the entities an EntityQuery returns from a scene. Predicates describe entities based on which components they contain, or on the entity’s relationship to other entities in the scene. For example, you can build a predicate to retrieve the model entities from a scene.

let modelPredicate = QueryPredicate.has(ModelComponent.self)

Create compound predicates

You can combine predicates using Swift’s logical operators to create compound predicates. QueryPredicate supports Swift’s logical AND (&&), logical OR (||), and logical NOT (!) operators. The following code shows how to build a compound predicate that returns all entities that are either model entities or anchor entities:

let orPredicate: QueryPredicate<Entity> =
    .has(ModelComponent.self) || .has(AnchorComponent.self)

Use parentheses to control the order of operations when combining predicates. For example, you can create a query that returns any entity that has both a model component and a physics body component, or any entity that has only an anchor component.

let multiPredicate: QueryPredicate<Entity> =
    .has(ModelComponent.self) && .has(PhysicsBodyComponent.self) ||
    .has(AnchorComponent.self)

Topics

Creating predicates

has(_:)