Aggregate isolation

[kfrajtak]

Hi,
I have some question about the aggregate isolation. I got the idea that in DDD the aggregate is immutable with read-only properties and the only way to change its internal state is via events and corresponding `Apply methods.

In Marten documentation example (https://martendb.io/scenarios/aggregates-events-repositories.html) it is discouraged in favor of decider pattern. The decider pattern removes the "platform specific" code from business logic - collecting the events, publishing messages, etc.

Does it mean that business logic is only implemented in the event handler and tested with the infrastructure in mind - i.e. verifying corresponding data was modified and some events published?

Thank you for help,
Karel