migration_0_5_0.md

Migrating guide to v0.5.0

v0.4.x ==> v0.5.0

Significant changes to the Aggregate::handle interface and operation

Several changes were made to the aggregate handler interface. These are:

• The method now requires that the aggregate be mutable.
• Events are now longer returned from the method.
• An EventSink struct is now used to write events (previously returned from the method).

async fn handle(&self, command: Self::Command, service: &Self::Services) -> Result<Vec<Self::Event>, Self::Error>

async fn handle(&mut self, command: Self::Command, service: &Self::Services, sink: &EventSink<Self>) -> Result<(), Self::Error>

Update command handler logic

Previously, writing an event was handled by returning it, within a vector, as the handle result. This logic should be modified to write the event to the provided EventSink. Additionally, a successful command should return an empty Ok(()).

Within the command handler logic, what was previously

let result: Vec<CustomerEvent> = Default::default();
result.append(CustomerEvent::CustomerAdded);

...

Ok(result)

or

return Ok(vec![CustomerEvent::CustomerAdded]);

Should be converted to:

sink.write(CustomerEvent::CustomerAdded, self)

...

Ok(())