Library for Command/Event support
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Key: QI-209
URL: http://issues.ops4j.org/browse/QI-209
Project: Qi4j
Issue Type: New Feature
Reporter: Niclas Hedhman
Assignee: Rickard Öberg
Fix For: 1.0
We should create a library to support a Commond/Event pattern, where commands
(methods in interfaces) triggers events which are recorded and can be played
back later in time.
The suggested solution is basically;
If a method is marked @Command, then the CommandQueueSideEffect is attached,
and will pass the invoked method to a CommandService, which will persist the
commands and allow the commands to be replayed later. This is all optional, as
Command playback has the disadvantage of not recreating the same UUIDs.
The typical mixin then goes on and implements the "Command" in a regular
fashion, and typically calls a number of methods on private mixins. And if
those are marked with @Event, the EventQueueConcern is attached, which will (if
in recording mode, done with ThreadLocal on EventQueueService) forward the
events to the EventService, which in turn will persist the events.
Upon startup, it is possible to tell the EventQueueService that 'playback' is
wanted. The EventQueueService will then locate each of the entities, and invoke
the methods on the @Event methods as previously.
The Events and Commands should be saved in a JSON format in a store optimized
for "adding" and "locate+enumerate" operations.
This will allow the domain model to rebuild the snapshot view from scratch at
any point in time.
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