Command pattern in php applications: how to handle controller actions?

Question

I think this is more of a general question (so not php restricted) with regards to ddd and the command pattern.

Let's say I execute a CreatePostCommand from within the create action of my controller, the command will be handled and eventually executed successfully. What's the appropriate way to notify the controller which response to return in case the command did fail or succeed? Given the command handler will fire a domain specific event, I could hook up the controller to the event, but that seems a quite awkward, also not appropriate for every situation (e.g. a post could be created somewhere else and the controller really doesn't know about this :) ).

public function createAction($title, $content)
{
    $this->commandBus->execute(new CreatePostCommand($title, $content);

    $this->render('…'); // what if the command execution failed?
}

Any thoughts on this?

Answer 1

I think if you are really trying to follow the DDD command pattern then you need to treat the command bus as a fire and forget asynchronous process that may take a long time to complete.

Consider immediately redirecting to a command verifier controller. It's up to the command verifier to actively check the status of the command and see if it worked.

In most cases, the command will have finished successfully and your verifier can then redirect once again to continue normal flow.

If the command fails then the verifier puts up an appropriate error message.

If the command is in progress then you can entire a redirect loop while informing the user that the command is in progress.

Something like:

// Execute the command
$command = new CreatePostCommand($title, $content);
$this->commandBus->execute($command);

return redirect '/command-verifier/' . $command->getId();

// The verification action
public function verifyCommandAction($commandId)

$commandStatus = $this->commandBus->getStatus($commandId);

if ($commandStatus == SUCCESS) redirect to all is well;

if ($commandStatus == FAILED) then oops;

if ($commandStatus == IN_PROGRESS) then maybe pause a bit and redirect again while keeping the user informed.

Clearly there is quite a bit of hand waving going on but I think this is the most general approach especially with php where every request starts from ground zero.