As presented at Dutch PHP Conference 2015, an introduction to command buses, how to implement your own in PHP and why they're both useful but unimportant.

1. Command Bus To
DPC 2015
Awesome Town
Ross Tuck

3. Command Bus To Awesome Town

4. This is a story...

5. ...about a refactoring.

6. $store->purchaseGame($gameId, $customerId);

7. Domain Model
Service
Controller
View

8. $store->purchaseGame($gameId, $customerId);

9. class BUYBUYBUYController
{
public function buyAction(Request $request)
{
$form = $this->getForm();
$form->bindTo($request);
if ($form->isTotallyValid()) {
$store->purchaseGame($gameId, $customerId);
return $this->redirect('thanks_for_money');
}
return ['so_many_errors' => $form->getAllTheErrors()];
}
}

10. class Store
{
public function purchaseGame($gameId, $customerId)
{
Assert::notNull($gameId);
Assert::notNull($customerId);
$this->security->allowsPurchase($customerId);
$this->logging->debug('purchasing game');
try {
$this->db->beginTransaction();
$purchase = new Purchase($gameId, $customerId);
$this->repository->add($purchase);
$this->db->commitTransaction();
} catch(Exception $e) {
$this->db->rollbackTransaction();
throw $e;
}
}
}

11. class Store
{
public function purchaseGame($gameId, $customerId)
{
$purchase = new Purchase($gameId, $customerId);
$this->repository->add($purchase);
}
}

12. $store->purchaseGame($gameId, $customerId);

13. ->purchaseGame($gameId, $customerId);
$store

14. purchaseGame($gameId, $customerId);
$store->

15. purchaseGame $gameId, $customerId ;
$store-> ( )

16. purchaseGame $gameId $customerId
$store-> ( , );

17. purchaseGame $gameId $customerId
Data

18. purchaseGame $gameId $customerId
Intent
Information

19. purchaseGame $gameId $customerId

20. PurchaseGame $gameId $customerId

21. PurchaseGame($gameId, $customerId);

22. new PurchaseGame($gameId, $customerId);

23. new PurchaseGame($gameId, $customerId);
->getGameId();
->getCustomerId();

24. new PurchaseGame($gameId, $customerId);

25. Object

26. Message

28. People Paperwork→
Machines Messages→

29. Different types of messages

30. Command

31. Reserve Seat

32. Reserve Seat
Schedule Appointment

33. new PurchaseGame($gameId, $customerId);
Reserve Seat
Schedule Appointment

34. Data Structure
Why object?

35. +------------+--------------+
| Field | Type |
+------------+--------------+
| id | varchar(60) |
| indication | varchar(255) |
| arrived | tinyint(1) |
| firstName | varchar(255) |
| lastName | varchar(255) |
| birthDate | datetime |
+------------+--------------+

37. struct purchase_game {
int game_id;
int customer_id;
}

38. Map[Int, Int]
Tuple[Int, Int]

39. [
'game_id' => 42,
'customer_id' => 11
]

40. class PurchaseGame
{
public $gameId;
public $customerId;
}

41. class PurchaseGame
{
private $gameId;
private $customerId;
public function __construct($gameId, $customerId)
{
$this->gameId = $gameId;
$this->customerId = $customerId;
}
public function getGameId()
{
return $this->gameId;
}
public function getCustomerId()
{
return $this->customerId;
}
}

42. class PurchaseController
{
public function purchaseGameAction(Request $request)
{
$form = $this->createForm('purchase_game');
$form->bind($request);
if ($form->isValid()) {
$command = $form->getData();
}
}
}

43. We have intent...

44. ...but no ability to carry out.

45. Command Handlers

46. Handlers handle commands

47. 1:1 Command to Handler

48. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
Assert::notNull($command->getGameId());
Assert::notNull($command->getCustomerId());
$this->security->allowsPurchase($command->getCustomerId());
$this->logging->debug('purchasing game');
try {
$this->db->beginTransaction();
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
$this->db->commitTransaction();
} catch(Exception $e) {
$this->db->rollbackTransaction();
throw $e;
}
}
}

49. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
$this->security->allowsPurchase($command->getCustomerId());
$this->logging->debug('purchasing game');
try {
$this->db->beginTransaction();
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
$this->db->commitTransaction();
} catch(Exception $e) {
$this->db->rollbackTransaction();
throw $e;
}
}
}

50. Command + Handler

51. $handler->handle(new PurchaseGame($gameId, $customerId));
$store->purchaseGame($gameId, $customerId);
“Extract To Message”

53. Command Message vs Command Pattern

54. $command = new PurchaseGame($gameId, $customerId);
$handler->handle($command);
Handler version

55. $command = new PurchaseGame($gameId, $customerId);

56. $command = new PurchaseGame($gameId, $customerId);
$command->execute();
Classical version

57. $command = new PurchaseGame($gameId, $customerId, $repository,
$db, $logger, $security);
$command->execute();
Classical version

58. ●
Game ID
●
Customer ID
Purchase THIS game Purchase ANY game
●
Repository
●
Security
●
Logger
●
DB

59. I generally advocate Handlers

60. Connecting the Dots

61. Command Handler

62. class PurchaseController
{
public function purchaseGameAction()
{
// form stuff lol
$command = $form->getData();
$this->handler->handle($command);
}
}
Controller
Must be
the RIGHT handler

63. Mailman

64. Enter the Bus

65. Command Bus

66. Handler
Command Bus
Command

67. Handler
Command Bus
Command

68. Handler
Command Bus
Command
♥♥
♥
♥
♥

69. So, what is this command bus?

70. new CommandBus(
[
PurchaseGame::class => $purchaseGameHandler,
RegisterUser::class => $registerUserHandler
]
);

71. $command = new PurchaseGame($gameId, $customerId);
$commandBus->handle($command);

72. ●
Over the Network
●
In a queue
●
Execute in process

73. class CommandBus
{
private $handlers = [];
public function __construct($handlers) {
$this->handlers = $handlers;
}
public function handle($command)
{
$name = get_class($command);
if (!isset($this->handlers[$name])) {
throw new Exception("No handler for $name");
}
$this->handlers[$name]->handle($command);
}
}

75. Easier to Wire

76. Handler Freedom

77. It's just conventions

78. class CommandBus
{
private $handlers = [];
public function __construct($handlers) {
$this->handlers = $handlers;
}
public function handle($command)
{
$name = get_class($command);
if (!isset($this->handlers[$name])) {
throw new Exception("No handler for $name");
}
$this->handlers[$name]->handle($command);
}
}

79. class CommandBus
{
private $handlers = [];
public function __construct($handlers) {
$this->handlers = $handlers;
}
public function handle($command)
{
$name = get_class($command);
if (!isset($this->handlers[$name])) {
throw new Exception("No handler for $name");
}
$this->handlers[$name]->execute($command);
}
}

80. class CommandBus
{
private $handlers = [];
public function __construct($handlers) {
$this->handlers = $handlers;
}
public function handle($command)
{
$name = get_class($command);
if (!isset($this->handlers[$name])) {
throw new Exception("No handler for $name");
}
$this->handlers[$name]->__invoke($command);
}
}

81. class CommandBus
{
private $handlers = [];
public function __construct($handlers) {
$this->handlers = $handlers;
}
public function handle($command)
{
$name = get_class($command);
if (!isset($this->handlers[$name])) {
throw new Exception("No handler for $name");
}
$methodName = 'handle'.$name;
$this->handlers[$name]->{$methodName}($command);
}
}

82. class CommandBus
{
private $handlers = [];
public function __construct($handlers) {
$this->handlers = $handlers;
}
public function handle($command)
{
$name = get_class($command);
if (!isset($this->handlers[$name])) {
throw new Exception("No handler for $name");
}
$this->handlers[$name]->handle($command);
}
}

83. class CommandBus
{
private $container = [];
public function __construct($container) {
$this->container = $container;
}
public function handle($command)
{
$name = get_class($command)."Handler";
if (!$this->container->has($name)) {
throw new Exception("No handler for $name");
}
$this->container->get($name)->handle($command);
}
}

84. It's just conventions

85. Plugins

86. Command Bus Uniform Interface→

87. ->handle($command);

89. Decorator Pattern

90. Command Bus 3
Command Bus 2
Command Bus

91. Command Bus 1
Command Bus 3
Command Bus 2

92. Command Bus 3
Command Bus 2
Command Bus

93. Command Bus 3
Logging Command Bus
Command Bus

94. Transaction Command Bus
Logging Command Bus
Command Bus

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

96. class CommandBus
{
private $handlers = [];
public function __construct($handlers) {
$this->handlers = $handlers;
}
public function handle($command)
{
$name = get_class($command);
if (!isset($this->handlers[$name])) {
throw new Exception("No handler for $name");
}
$this->handlers[$name]->handle($command);
}
}

97. class MyCommandBus
{
private $handlers = [];
public function __construct($handlers) {
$this->handlers = $handlers;
}
public function handle($command)
{
$name = get_class($command);
if (!isset($this->handlers[$name])) {
throw new Exception("No handler for $name");
}
$this->handlers[$name]->handle($command);
}
}

98. class MyCommandBus implements CommandBus
{
private $handlers = [];
public function __construct($handlers) {
$this->handlers = $handlers;
}
public function handle($command)
{
$name = get_class($command);
if (!isset($this->handlers[$name])) {
throw new Exception("No handler for $name");
}
$this->handlers[$name]->handle($command);
}
}

99. What to refactor out?

100. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
$this->security->allowsPurchase($command->getCustomerId());
$this->logging->debug('purchasing game');
try {
$this->db->beginTransaction();
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
$this->db->commitTransaction();
} catch(Exception $e) {
$this->db->rollbackTransaction();
throw $e;
}
}
}

101. class LoggingDecorator implements CommandBus
{
private $logger;
private $innerBus;
public function __construct(Logger $logger, CommandBus $innerBus)
{
$this->logger = $logger;
$this->innerBus = $innerBus;
}
public function handle($command)
{
$this->logger->debug('Handling command '.get_class($command));
$this->innerBus->handle($command);
}
}

102. class LoggingDecorator implements CommandBus
{
private $logger;
private $innerBus;
public function __construct(Logger $logger, CommandBus $innerBus)
{
$this->logger = $logger;
$this->innerBus = $innerBus;
}
public function handle($command)
{
$this->innerBus->handle($command);
$this->logger->debug('Executed command '.get_class($command));
}
}

103. class LoggingDecorator implements CommandBus
{
private $logger;
private $innerBus;
public function __construct(Logger $logger, CommandBus $innerBus)
{
$this->logger = $logger;
$this->innerBus = $innerBus;
}
public function handle($command)
{
$this->logger->debug('Handling command '.get_class($command));
$this->innerBus->handle($command);
$this->logger->debug('Executed command '.get_class($command));
}
}

104. $commandBus = new LoggingDecorator(
$logger,
new MyCommandBus(...)
);
$commandBus->handle($command);

106. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
$this->security->allowsPurchase($command->getCustomerId());
$this->logging->debug('purchasing game');
try {
$this->db->beginTransaction();
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
$this->db->commitTransaction();
} catch(Exception $e) {
$this->db->rollbackTransaction();
throw $e;
}
}
}

107. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
$this->security->allowsPurchase($command->getCustomerId());
try {
$this->db->beginTransaction();
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
$this->db->commitTransaction();
} catch(Exception $e) {
$this->db->rollbackTransaction();
throw $e;
}
}
}

108. Ridiculously Powerful

109. Redonkulously Powerful

110. Why not Events?

111. Cohesion

112. Execution

113. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
$this->security->allowsPurchase($command->getCustomerId());
try {
$this->db->beginTransaction();
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
$this->db->commitTransaction();
} catch(Exception $e) {
$this->db->rollbackTransaction();
throw $e;
}
}
}

114. Let's Decoratorize
TM

115. class TransactionDecorator implements CommandBus
{
private $db;
private $innerBus;
public function __construct($db, $innerBus)
{
$this->db = $db;
$this->innerBus = $innerBus;
}
public function handle($command)
{
try {
$this->db->beginTransaction();
$this->innerBus->handle($command);
$this->db->commitTransaction();
} catch (Exception $e) {
$this->db->rollbackTransaction();
throw $e;
}
}
}

116. The Handler?

117. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
$this->security->allowsPurchase($command->getCustomerId());
try {
$this->db->beginTransaction();
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
$this->db->commitTransaction();
} catch(Exception $e) {
$this->db->rollbackTransaction();
throw $e;
}
}
}

118. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
$this->security->allowsPurchase($command->getCustomerId());
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
}
}

120. ...Wait, all the Commands?

121. Limiting which decorators run

122. Marker Interface

123. $this->security->allowsPurchase($command->getCustomerId());

124. interface PurchaseCommand
{
public function getCustomerId();
}

125. class PurchaseGame
{
private $gameId;
private $customerId;
// constructors, getters, etc
}

126. class PurchaseGame implements PurchaseCommand
{
private $gameId;
private $customerId;
// constructors, getters, etc
}

127. class AllowedPurchaseDecorator implements CommandBus
{
private $security;
private $innerBus;
public function __construct($security, $innerBus)
{
$this->security = $security;
$this->innerBus = $innerBus;
}
public function handle($command)
{
if ($command instanceof PurchaseCommand) {
$this->security->allowPurchase($command->getCustomerId());
}
$this->innerBus->handle($command);
}
}

128. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
$this->security->allowsPurchase($command->getCustomerId());
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
}
}

129. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
}
}

130. class PurchaseGameHandler
{
public function handle(PurchaseGame $command)
{
$purchase = new Purchase(
$command->getGameId(),
$command->getCustomerId()
);
$this->repository->add($purchase);
}
}
Stop cutting!

131. Beyond Decorators

132. new AllowedPurchaseDecorator(
$security,
new TransactionDecorator(
$db,
new LoggingDecorator(
$logger,
new MyCommandBus(
[
PurchaseGame::class => $purchaseGameHandler
]
)
)
)
)

133. Constructor Parameter
Method

134. interface Middleware {
public function handle($command, callable $next);
}

135. class LoggingMiddleware implements Middleware
{
private $logger;
public function __construct($logger)
{
$this->logger = $logger;
}
public function handle($command, callable $next)
{
$this->logger->debug('handling '.get_class($command));
next($command);
}
}

136. new CommandBus(
[
new AllowedPurchaseMiddleware($security),
new TransactionMiddleware($db),
new LoggingMiddleware($logger),
new CommandHandlerMiddleware($handlerMapping),
]
);

137. 5 Things That I Have Seen

138. Thing #1
Handling Commands in Commands

139. Domain Model
Service
Controller
View
PurchaseGameSendConfirmation

140. If it needs to happen with the command…
JUST CALL IT

141. If it needs to happen after the command…
Wait for a domain event

142. Thing #2
Reading From Commands
Or the lack thereof

143. “Command Bus should never return anything.”

144. Command Bus != CQRS

145. $commandBus->handle(new PurchaseGame($gameId, $customerId));
$store->purchaseGame($gameId, $customerId);

146. $commandBus->handle(new PurchaseGame($gameId, $customerId));
$id = $this
->domainEvents
->waitFor(GamePurchased::class)
->getId();

147. Thing #3
Reading with a Command Bus

148. $handler->handle(new PurchaseGame($gameId, $customerId));
$this->repository->findPurchaseById($id);
$this->readService->findPurchaseVerification($id);
$this->queryBus->find(new PurchaseById($id));

149. Thing #4
Command Buses Work Great in JS

150. commandBus.handle({
"command": "purchase_game",
"game_id": gameId,
"customer_id": customerId
});

151. Thing #5
Single Endpoint “REST”

152. /commands

153. /purchase-game

154. The Meta of Command Buses

155. Why are there 50 of them?

159. μ

160. function createBus($handlers) {
return function ($command) use ($handlers) {
$handlers[get_class($command)]($command);
};
}

161. $bus = createBus(
[
FooCommand::class => $someClosure,
BarCommand::class => $someOtherClosure
]
);
$cmd = new FooCommand();
$bus($cmd);

162. But you should use my library.

165. Command Bus Libraries are useless

166. ...but the plugins aren't.

168. Me
tactician-doctrine
tactician-logger
named commands
locking

169. @sagikazarmark
tactician-bernard
tactician-command-events

170. @boekkooi tactician-amqp

171. @rdohms
@xtrasmal
@Richard_Tuin
tactician-bundle

172. @GeeH
@mike_kowalsky
tactician-module

173. Prasetyo Wicaksono
Eugene Terentev
Jildert Miedema
Nigel Greenway
Frank de Jonge
Ivan Habunek
tactician-service-provider
yii2-tactician
laravel-tactician
tactician-container
tactician-awesome-advice
tactician-pimple

174. Shared Interfaces

175. The Future of Tactician

176. ● Simplify Interfaces
● Metadata
● Tracking
● RAD

177. Domain Model
Service
Controller
View

178. SimpleBus
Broadway

179. Command
Handler
Bus
Decorators
executes
connects extends

180. Command Handler

181. The End

182. Images
● http://bj-o23.deviantart.com/art/NOT-Rocket-Science-324795055
● sambabulli.blogsport.de
● https://www.youtube.com/watch?v=XHa6LIUJTPw
● http://khongthe.com/wallpapers/animals/puppy-bow-227081.jpg
● https://www.flickr.com/photos/emptyhighway/7173454/sizes/l
● https://www.flickr.com/photos/jronaldlee/5566380424

183. domcode.org
Ross Tuck
@rosstuck
joind.in/14219
PHPArchitectureTour.com