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Handling validation with a command bus

I've been struggling with coming up with a way to handle validation in my command bus architecture.

Throwing validation exceptions in middleware felt wrong. Those aren't really exceptional occurences. Validating data outside of the bus(in controllers/console commands) felt wrong. Validation could be easily side-stepped. Validating in handlers felt cluttered and seemed to violate the SRP.

I think I've finally come up with something I'm fairly happy with though.

What I tried first

Return new ArrayCollections from getters

Do you have some business logic tied up in your adder methods? Something like this maybe.

class Cart
{
	private $items;

	public function __construct()

Start throwing "not found" exceptions in your repositories

99% of the time you're going to want to bail if you're expecting to find an entity by a specific key. Having code like the two private methods in the old code below in every single one of your handlers is crazy and not DRY.

I think the idea of "only throw exceptions when something exceptional happens" is too generic and doesn't take context into consideration.

A repository's only job is to find entities. If you give it a key and it can't find it, i think that's exceptional(in the context of the repository).

If it actually is expected in your client code it's not a big deal, catch the EntityNotFoundException and carry on.

	ENV.contentSecurityPolicy = {
	'default-src': "'none'",
	'script-src': "'self' http://192.168.56.120",
	'font-src': "'self'",
	'connect-src': "'self' ws://192.168.56.120",
	'img-src': "'self'",
	'style-src': "'self'",
	'media-src': "'self'"
	};

	<?php

	class UserHydrator
	{
	private $user;

	private $resolver;

	public function __construct(User $user)
	{

	<?php

	use App\Models\Company;
	use Illuminate\Database\Eloquent\Builder;

	class CompanyController extends \BaseController
	{
	/**
	* Display a listing of the resource.
	*

	<?php

	use SimpleBus\Message\Message;

	interface CommandPipe
	{
	/**
	* @param Message $command
	* @param callable $next
	*/

	<?php

	namespace Acme\Project\Infrastructure\AppBundle\DependencyInjection;

	use Symfony\Component\DependencyInjection\ContainerBuilder;
	use Symfony\Component\Config\FileLocator;
	use Symfony\Component\HttpKernel\DependencyInjection\Extension;
	use Symfony\Component\DependencyInjection\Loader;

	/**

	<?php

	namespace Acme\Project\Infrastructure\AppBundle\Middleware;

	use SimpleBus\Message\Handler\MessageHandler;
	use SimpleBus\Message\Message;

	class CommandHandlerSupportingLazyMiddleware implements MessageHandler
	{
	/**

	<?php

	namespace Acme\AwesomeApp\Infrastructure\UserBundle\Features\Context;

	use Behat\Behat\Context\Context;
	use Behat\Behat\Context\Environment\InitializedContextEnvironment;
	use Behat\Behat\Context\SnippetAcceptingContext;
	use Behat\Behat\Hook\Scope\BeforeScenarioScope;
	use Acme\AwesomeApp\Domain\User\Entity\User;
	use Acme\AwesomeApp\Domain\User\Security\PasswordEncoder;