Taming Command Bus

Taming

Command Bus

Krzysztof Menżyk @kmenzyk

About me

Technical Leader at Test infectedBelieves that software is a craftLoves domain modelling

Homebrewer & squash player

This talk is not

This talk is not

DDD*

This talk is not

CQRS*

Back to the

PAST

BEGANIt all

with ...

class ProductController extends Controller{ //...

public function updateAction($id) { if (false === $this->get('security.context')->isGranted('ROLE_ADMIN')) { throw new AccessDeniedException(); }

$em = $this->getDoctrine()->getManager(); $product = $em->getRepository('AcmeDemoBundle:Product')->find($id);

if (!$product) { throw $this->createNotFoundException('Unable to find Product entity.'); }

$request = $this->getRequest(); $editForm = $this->createForm(new ProductType(), $product); $editForm->bind($request);

if ($editForm->isValid()) { $product->setLastUpdated(new \DateTime); $em->flush();

$message = \Swift_Message::newInstance() ->setSubject('Product updated') ->setFrom($this->container->getParameter('acme.product_email.from')) ->setTo($this->container->getParameter('acme.product_email.to')) ->setBody($this->renderView( 'AcmeDemoBundle:Product:email.txt.twig', array('product' => $product)) ) ; $this->get('mailer')->send($message);

return $this->redirect( $this->generateUrl('product', array('id' => $id)) ); }

return new Response( $this->renderView( 'AcmeDemoBundle:Product:edit.html.twig', array( 'product' => $product, 'edit_form' => $editForm->createView(), ) ) ); }}

Controller Driven Design

„approach”



















LAYERS

Presentation

Presentation

Domain

Presentation

Service

Domain

Presentation

Service

Domain

Infrastructure

Presentation

Service

Domain

Infrastructure

Defines an application's boundary with a layer of services.

Service Layer

Establishes set of available operations.

Service Layer

Coordinates the application's response in each operation.

Service Layer

USE Cases

USER STORIES

Application Layer

class Library{ public function borrowBook($bookId, $readerId) { // ... }}

class LibraryController{ public function borrowAction(ServerRequestInterface $request) { // Forms, etc.

$this->library->borrowBook($bookId, $readerId); // Response }}

class Library{ public function borrowBook($bookId, $readerId) { if (null === $bookId || null === $readerId) { throw new \InvalidArgumentException(); }

$this->logging->debug('A reader is borrowing a book');

$this->connection->beginTransaction(); try { $book = $this->books->get($bookId); $book->borrowBy($readerId); $this->books->add($book); $this->connection->commit(); } catch (\Exception $e) { $this->connection->rollBack(); $this->logging->debug('Ooops! Bad luck.'); throw $e; }

$this->logging->debug('Success!'); }}

















borrowBook($bookId, $readerId)

new BorrowBook($bookId, $readerId)

COMMAND

not a class/objectMESSAGE

Messaging Flavors

by @mathiasverraes

Messaging Flavors

by @mathiasverraes

Imperative

Messaging Flavors

by @mathiasverraes

Imperative

Command

Messaging Flavors

by @mathiasverraes

Imperative Interrogatory

Command

Messaging Flavors

by @mathiasverraes

Imperative Interrogatory

Command QUERY

Messaging Flavors

by @mathiasverraes

Imperative Interrogatory Informational

Command QUERY

Messaging Flavors

by @mathiasverraes


Command QUERY EVENT

Messaging Flavors

by @mathiasverraes


Command QUERY EVENT

Captures

THE INTENTof the user

Supports

UbiquitousLANGUAGE

Borrow BookGive Book BackRegister User

Start SubscriptionHire Employee

Contains

THE INPUTto carry out the task

final class BorrowBook{ public $bookId; public $readerId;

public function __construct($bookId, $readerId) { $this->bookId = $bookId; $this->readerId = $readerId; }}

Should be

IMMUTABLE

final class BorrowBook{ private $bookId; private $readerId;

public function __construct($bookId, $readerId) { $this->bookId = $bookId; $this->readerId = $readerId; }

public function getBookId() { return $this->bookId; }

public function getReaderId() { return $this->readerId; }}

Must be

VALID

final class BorrowBook{ private $bookId; private $readerId;

public function __construct($bookId, $readerId) { Assertion::notNull($bookId); Assertion::notNull($readerId); $this->bookId = $bookId; $this->readerId = $readerId; }

public function getBookId() { return $this->bookId; }

public function getReaderId() { return $this->readerId; }}

INTERPRETHow to

a command?

COMMANDHandler

per commandONE HANDLER

Returns

NO VALUE

final class BorrowBookHandler{ public function handle(BorrowBook $command) { $this->logging->debug('A reader is borrowing a book');

$this->connection->beginTransaction();

try { $book = $this->books->get($command->getBookId()); $book->borrowBy($command->getReaderId());

$this->books->add($book);

$this->connection->commit(); } catch (\Exception $e) { $this->connection->rollBack();

$this->logging->debug('Ooops! Bad luck.');

throw $e; }








throw $e; }


One more thing ...

The BUS

COMMANDBUS

Hands over

THE COMMANDto

THE HANDLEr

Handler C

CommandBus

Handler BHandler A

Handler C

Command C

CommandBus

Handler BHandler A

Handler C

CommandBus

Handler BHandler A

Command C

Handler C

CommandBus

Handler BHandler A Command C

Handler C

CommandBus

Handler BHandler A

Single

ENTRY POINTto the application

interface CommandBus{ public function handle($command);}

class LibraryController{ public function borrowAction(ServerRequestInterface $request) { // Forms, etc.

$this->commandBus->handle(new BorrowBook($bookId, $readerId));

// Response }}

class SomeOtherController{ public function someOtherAction(ServerRequestInterface $request) { // Forms, etc.

$command = $form->getData(); $this->commandBus->handle($command);

// Response }}

class SomeOtherController{ public function someOtherAction(ServerRequestInterface $request) { // Forms, etc.

$command = $form->getData(); $this->commandBus->handle($command);

// Response }}

class BorrowBookCli{ protected function execute(InputInterface $input, OutputInterface $output) { // get $command from the input somehow $this->commandBus->handle($command);

// ... }}

IMPLEMENTLet's

the stupid thing

class SimpleCommandBus implements CommandBus{ private $handlers;

public function __construct(array $handlers) { $this->handlers = $handlers; }

public function handle($command) { $commandName = get_class($command);

if (!isset($this->handlers[$commandName])) { throw new \InvalidArgumentException('No handler'); } $this->handlers[$commandName]->handle($command); }}

new SimpleCommandBus([ BorrowBook::class => $borrowBookHandler, GiveBookBack::class => $giveBookBackHandler,]);

That's it?

Do not

TRY ITat home

class SimpleCommandBus implements CommandBus{ private $handlers;

public function __construct(array $handlers) { $this->handlers = $handlers; }

public function handle($command) { $commandName = get_class($command);

if (!isset($this->handlers[$commandName])) { throw new \InvalidArgumentException('No handler'); } $this->handlers[$commandName]->handle($command); }}

Cross cutting concerns

interface CommandBus{ public function handle($command);}

DECORATOR

class CommandBusWithAddedBehavior implements CommandBus{ public function __construct(CommandBus $originalCommandBus) { $this->originalCommandBus = $originalCommandBus; }

public function handle($command) { // do anything you want

$this->originalCommandBus->handle($command);

// do even more }}

new CommandBusWithAddedBehavior( new SimpleCommandBus([ BorrowBook::class => $borrowBookHandler, GiveBookBack::class => $giveBookBackHandler, ]));

Command Bus

Decorator

Decorator

Command







throw $e; }


class TransactionalCommandBus implements CommandBus{ public function __construct($innerCommandBus, $connection) { $this->innerCommandBus = $innerCommandBus; $this->connection = $connection; }

public function handle($command) { $this->connection->beginTransaction(); try { $this->innerCommandBus->handle($command); $this->connection->commit(); } catch (\Exception $exception) { $this->connection->rollBack();

throw $e; } }}







throw $e; }


class LoggingCommandBus implements CommandBus{ public function __construct($innerCommandBus, $logger) { $this->innerCommandBus = $innerCommandBus; $this->logger = $logger; }

public function handle($command) { $commandClass = get_class($command);

$this->logger->debug('Started handling ' . $commandClass);

try { $this->innerCommandBus->handle($command); } catch (\Exception $exception) { $this->logger->debug('Error while handling ' . $commandClass);

throw $e; }

$this->logger->debug('Finished handling ' . $commandClass); }}







throw $e; }


final class BorrowBookHandler{ public function handle(BorrowBook $command) { $book = $this->books->get($command->getBookId()); $book->borrowBy($command->getReaderId());

$this->books->add($book);'Success!'); }}

Easy to

TEST

But...

new LoggingCommandBus( new TransactionalCommandBus( new SimpleCommandBus([ BorrowBook::class => $borrowBookHandler, GiveBookBack::class => $giveBookBackHandler, ]), $connection ), $logger);

Can we do better?

Yes

We can!

CHAIN OF RESPONSIBILITY

interface CommandBusMiddleware{ public function handle($command, callable $next);}

Command Handler

Middleware

Command

Middleware

Middleware

class AddedBehaviorMiddleware implements CommandBusMiddleware{ public function handle($command, callable $next) { // do anything you want

$next($command);

// do even more }}

new CommandBusSupportingMiddleware([ new AddedBehaviorMiddleware(), new CommandHandlerMiddleware([ BorrowBook::class => $borrowBookHandler, GiveBookBack::class => $giveBookBackHandler, ])]);

new CommandBusSupportingMiddleware([ new LoggingMiddleware($logger), new TransactionalMiddleware($connection), new CommandHandlerMiddleware([ BorrowBook::class => $borrowBookHandler, GiveBookBack::class => $giveBookBackHandler, ])]);

TransactionsLoggingSecurity

Performance MetricsAudit log

You name it

Command Bus libraries

by @matthiasnobackSimple Bus

by @rosstuckTACTICIAN

by @qandidate-labsBROADWAY

Use them and contribute

Like we

DID

Krzysztof Menżyk @kmenzyk

Thanks!

Taming Command Bus

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Taming Command Bus

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