Hi,
I have now made an initial commit of an EventSourcing library in
qi4j-libraries. Basically, when making changes to a domain model it is
possible to mark entity methods as @DomainEvent, which will then cause a
domain event to be created. When the UoW commits all the events in it
will be stored as a unit in an EventStore. They can then be consumed
either by a listener interface (push) or a direct access interface
(poll). There are helpers available that makes it easy to consume events
without having to bother with whether to do poll (if you're behind) or
push (if you're up to date).
Here's an example from the test code:
Principal administratorPrincipal = ...
UnitOfWork uow = unitOfWorkFactory.newUnitOfWork(
UsecaseBuilder.newUsecase( "Change description" ));
uow.metaInfo().set( administratorPrincipal );
TestEntity entity = uow.newEntity( TestEntity.class );
entity.changedDescription( "New description" );
uow.complete();
EventSource source = (EventSource) serviceLocator.findService(
EventSource.class ).get();
source.events( 0, Long.MAX_VALUE ).transferTo( Transforms.map( new
Function<UnitOfWorkDomainEventsValue, String>()
{
public String map( UnitOfWorkDomainEventsValue
unitOfWorkDomainEventsValue )
{
return unitOfWorkDomainEventsValue.toJSON();
}
}, Outputs.systemOut()));
---
which will output:
{"events":[{"entityId":"8de8d219-352e-4a37-a5c8-4f9db8db96b4-0","entityType":"org.qi4j.library.eventsourcing.domain.DomainEventTest$TestEntity","name":"changedDescription","parameters":"{\"param0\":\"New
description\"}"}],"timestamp":1295427369412,"usecase":"Change
description","user":"administrator","version":"1.0"}
To define the EventSourced method is as simple as:
@Mixins( TestEntity.Mixin.class )
public interface TestEntity
extends EntityComposite
{
@UseDefaults
Property<String> description();
@DomainEvent
void changedDescription( String newName );
abstract class Mixin
implements TestEntity
{
public void changedDescription( String newName )
{
description().set( newName );
}
}
}
---
i.e. annotation is enough.
So that's a start. More to be done on helpers, performance, and an Atom
feed for distribution.
Any thoughts/comments?
/Rickard
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