Module events 

Entity events report creation, explicitly supplied initial values, and later property changes:

• EntityCreatedEvent is emitted when an entity has been created.
• PropertyInitializedEvent is emitted for each non-default, non-derived property value explicitly supplied during creation.
• PropertyChangeEvent is emitted when a property is subsequently updated.

Client code can subscribe to these events with the Context::subscribe_to_event<IxaEvent>(handler) method:

// Suppose `InfectionStatus` is a property of the entity `Person`.
// A type alias for property change events makes code more concise and readable.
pub type InfectionStatusEvent = PropertyChangeEvent<Person, InfectionStatus>;
// Suppose we want to execute the following function whenever `InfectionStatus` changes.
fn handle_infection_status_change(context: &mut Context, event: InfectionStatusEvent){
    // ... handle the infection status change event ...
}
// We do so by subscribing to this event.
context.subscribe_to_event::<InfectionStatusEvent>(handle_infection_status_change);

// Observe a non-default value explicitly supplied when a person is created.
context.subscribe_to_event(
    |_context, event: PropertyInitializedEvent<Person, InfectionStatus>| {
        // ... use event.entity_id and event.value ...
    },
);

A non-derived property sits on the type-erased side of the boundary of its dependent’s PropertyValueStore, so it needs to somehow trigger the creation of and emit the change events for its dependents in a type-erased way.

Property change events are triggered and collected on the outside of the type-erased PropertyValueStore boundary, because a non-derived p

Structs

EntityCreatedEvent

Emitted when a new entity is created. These should not be emitted outside this module.

PropertyChangeEvent

Emitted when a property is updated. These should not be emitted outside this module.

PropertyInitializedEvent

Emitted for a non-default, non-derived property value supplied when an entity is created.