The possibility to use event machine (temporary) without event store aspect

[ebezdomnikov]

The possibility to use event machine (temporary) without event store aspect

[ebezdomnikov]

Hi @codeliner!

Thank you for the quick response. Actually, the "onlyWithPreProcessor" feature is what I need to start the migration and to get all event machine functionality on board for the future!

Looking forward to that feature:)

Thanks a lot.

[codeliner]

@ebezdomnikov New release available: https://github.com/proophsoftware/event-machine/releases/tag/v0.21.0

the linked PR contains a new test case and a small addition to Event Machine.

A preprocessor can add a command metadata flag return $command->withAddedMetadata(EventMachine::CMD_METADATA_STOP_DISPATCH, true);

to tell Event Machine that command dispatch should be stopped.

I've also prepared a gist for you. With a custom Flavour you can hook into preprocessor calls and f.e. check if a preprocessor implements a command handler interface (or whatever you want to use). This way you can migrate step by step. Let me know if something is unclear.

[codeliner]

Hey @ebezdomnikov thank you for your request.

Just to make sure: Within your command handlers you want to use ORM baked entities, like Doctrine entities?

The problem is, Event Machine is based on the idea of a functional core

You cannot/should not use I/O related services like an entity repository in the core of the system. To enforce this rule Event Machine does not provide a way to inject services into the domain model. You can only work with so called context providers, which are called beforehand.

That said, the only option I can think of is to provide some kind of alternative command handling.
Event Machine can invoke command preprocessors. The idea is that a preprocessor can enrich a command with additional information (f.e. specific metadata not sent by the client) before it is passed to the domain model.
We could tell Event Machine to only invoke a command preprocessor but stop right after that. The API would look like this (needs to be added to Event Machine but is an "easy-pick"):

$eventMachine->process(Command::ADD_BUILDING)
    ->onlyWithPreProcessor(Acme\PreProcessor::class);

What you do within the preprocessor is out of scope of Event Machine. You could even use your own Flavour so that your command handlers don't need to implement a specific interface and don't need to return anything (a preprocessor normally should return a modified command that is than passed on to an aggregate function).

What do you think? Would that be useful for your case?

[ebezdomnikov]

@codeliner Hi!

Thank you very much!!!