= @Collection
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Domain semantics for domain object collection.

== API

[source,java]
.Collection.java
----
@interface Collection {
  Class<? extends CollectionDomainEvent<?, ?>> domainEvent() default CollectionDomainEvent.Default.class;     // <.>
  Class<?> typeOf() default // represents unspecified
void.class;     // <.>
}
----

<.> xref:#domainEvent[domainEvent]
+
--
Indicates that changes to the collection that should be posted to the _org.apache.causeway.applib.services.eventbus.EventBusService event bus_ using a custom (subclass of) xref:refguide:applib:index/events/domain/CollectionDomainEvent.adoc[CollectionDomainEvent] .
--
<.> xref:#typeOf[typeOf]
+
--
The type-of the elements held within the collection.
--

== Members

[#domainEvent]
=== domainEvent

Indicates that changes to the collection that should be posted to the _org.apache.causeway.applib.services.eventbus.EventBusService event bus_ using a custom (subclass of) xref:refguide:applib:index/events/domain/CollectionDomainEvent.adoc[CollectionDomainEvent] .

Subscribers of this event can interact with the business rule checking (hide, disable, validate) and its modification (before and after).

For example:

----
public class Order {
  public static class OrderLineItems extends CollectionDomainEvent { ... }

  @CollectionInteraction(OrderLineItems.class)
  public SortedSet<OrderLine> getLineItems() { ...}
}
----

This subclass must provide a no-arg constructor; the fields are set reflectively.

[#typeOf]
=== typeOf

The type-of the elements held within the collection.

This is only provided as a fallback; usually the framework can infer the element type of the collection from the collection method's generic type.

include::hooks/Collection_010-examples-and-usage.adoc[]

include::hooks/Collection_021_domainEvent.adoc[]

include::hooks/Collection_022_hidden.adoc[]

include::hooks/Collection_023_typeOf.adoc[]
