What happened?

An introduction to CQRS and event sourcing in PHP

Transcript

2. What happened? An introduction to CQRS and event sourcing in PHP August 21st, 2014
3. Marijn Huizendveld
4. Tickets verkoop je met Pink Tie
5. Spaghetti monster
6. @marijn
7. @huizendveld
8. Interrupt me
9. Command Query Responsibility Segregation
10. Event Sourcing
11. Domain Driven Design
12. Fancy words
13. Big ideas
14. But difficult to explain
15. Tonight 1. Context: complex applications 2. CQRS: why and how? 3. Event Sourcing to the rescue
16. Tonight 1. Context: complex applications 2. CQRS: why and how? 3. Event Sourcing to the rescue
17. Complex applications
18. Valuable data
19. Changing environment
20. Applications that support the competitive advantage
21. Applications that empower the organization to fulfil its goals
22. Building them is a difficult job
23. Unknown territory
24. Ever changing environment
25. Tight budgets
26. High expectations
27. Pressure from the business
28. Questionable understanding
29. Who is currently building a complex application?
30. Are you responsible for front-end development?
31. Are you responsible for database administration?
32. Are you responsible for user experience?
33. Are you responsible for back-end development?
34. Are you responsible for business value?
35. Are you responsible for project management?
36. Are you responsible for system administration?
37. Current situation
39. RDBMS
40. NoSQL
41. CREATE
    READ
    UPDATE
    DELETE
42. CREATE
43. POST /products
44. INSERT INTO product (name, version) VALUES (“iPhone”, 6)
45. READ
46. GET /products/iphone
47. SELECT * FROM product WHERE name = “iPhone”
    AND version > 5
48. UPDATE
49. PATCH /products/iphone
50. UPDATE product SET available = 0
    WHERE version < 5
51. DELETE
52. DELETE /products/iphone
53. DELETE product WHERE version < 4
54. We OOP
55. <?php ! final class Product { private $id; private $name; ! public function __construct($aName) { $this->name = (string) $aName; } ! public function getId() { return $this->id; } ! public function getName() { return $this->id; } }
56. Enter ORM
57. <?php ! $iPhone = new Product('iPhone'); ! $entityManager->persist($iPhone); $entityManager->flush();
58. INSERT INTO product VALUES (“iPhone”)
59. But…
60. <?php ! class Customer { private $id; private $name; private $address; private $gender; ! public function getName() { return $this->name; } public function getAddress() { return $this->address; } public function getGender() { return $this->gender; } ! public function setName($name) { $this->name = $name; } public function setAddress($address) { $this->address = $address; } public function setGender($gender) { $this->gender = $gender; } }
62. DELETE /products/iphone
63. UPDATE product SET available = 0
    WHERE version < 5
64. <?php ! /** * Publications are the contextual point for all other objects * * @author Marijn Huizendveld <marijn@debaasmedia.nl> * @version $Revision: 163 $ changed by $Author: buroknapzak $ * * @copyright De Baas Media (2010) */ class kluPublicationPeer extends BasekluPublicationPeer { /** * Select the publications that have recently been updated. * * @param string $arg_connection * * @return array */ static public function retrieveRecentlyUpdatedForDomain ($arg_domainUnifiedResourceName = NULL, $arg_connection = NULL) { $sql = "SELECT * FROM (SELECT `publications`.`id` AS ID " . ", `publications`.`name` AS NAME " . ", `publications`.`unified_resource_name` AS UNIFIED_RESOURCE_NAME " . ", `publications`.`domain_unified_resource_name` AS DOMAIN_UNIFIED_RESOURCE_NAME " . ", `publications`.`introduction` AS INTRODUCTION " . ", `publications`.`created_at` AS CREATED_AT " . ", MAX(`revision_requests`.`applied_at`) AS UPDATED_AT " . ", `publications`.`deleted_at` AS DELETED_AT " . "FROM `revision_requests` " . "LEFT JOIN `updates` " . "ON (`updates`.`id` = `revision_requests`.`update_id`) " . "LEFT JOIN `update_collections` " . "ON `updates`.`collection_unified_resource_name` = `update_collections`.`unified_resource_name` " . "LEFT JOIN `publications` " . "ON (`publications`.`id` = `revision_requests`.`publication_id`) " . "WHERE `updates`.`revision_request_id` IS NULL " . "AND `publications`.`deleted_at` IS NULL " . "AND `publications`.`domain_unified_resource_name` = ? " . "AND `update_collections`.`publish_at` <= NOW() " . "AND `update_collections`.`publish_until` > NOW() " . "GROUP BY `revision_requests`.`publication_id` " . "ORDER BY `updated_at` DESC) " . "`publications` ORDER BY `updated_at` DESC"; $connection = NULL === $arg_connection ? Propel::getConnection(self::DATABASE_NAME) : $arg_connection; $statement = $connection->prepareStatement($sql); return self::populateObjects($statement->executeQuery(array(0 => $arg_domainUnifiedResourceName), ResultSet::FETCHMODE_NUM)); } }
65. Awesome?
66. For general purpose software?
67. Yes!
68. For complex applications?
69. No!
70. Why not?
71. Anemic domain model
72. <?php ! class Customer { private $id; private $name; private $address; private $gender; ! public function getName() { return $this->name; } public function getAddress() { return $this->address; } public function getGender() { return $this->gender; } ! public function setName($name) { $this->name = $name; } public function setAddress($address) { $this->address = $address; } public function setGender($gender) { $this->gender = $gender; } }
73. Non-intuitive interfaces
75. Valuable data is continuously lost
76. DELETE /products/iphone
77. Lacks context and expressiveness
78. UPDATE product SET available = 0
    WHERE version < 5
79. Querying and reporting are difficult
80. <?php ! /** * Publications are the contextual point for all other objects * * @author Marijn Huizendveld <marijn@debaasmedia.nl> * @version $Revision: 163 $ changed by $Author: buroknapzak $ * * @copyright De Baas Media (2010) */ class kluPublicationPeer extends BasekluPublicationPeer { /** * Select the publications that have recently been updated. * * @param string $arg_connection * * @return array */ static public function retrieveRecentlyUpdatedForDomain ($arg_domainUnifiedResourceName = NULL, $arg_connection = NULL) { $sql = "SELECT * FROM (SELECT `publications`.`id` AS ID " . ", `publications`.`name` AS NAME " . ", `publications`.`unified_resource_name` AS UNIFIED_RESOURCE_NAME " . ", `publications`.`domain_unified_resource_name` AS DOMAIN_UNIFIED_RESOURCE_NAME " . ", `publications`.`introduction` AS INTRODUCTION " . ", `publications`.`created_at` AS CREATED_AT " . ", MAX(`revision_requests`.`applied_at`) AS UPDATED_AT " . ", `publications`.`deleted_at` AS DELETED_AT " . "FROM `revision_requests` " . "LEFT JOIN `updates` " . "ON (`updates`.`id` = `revision_requests`.`update_id`) " . "LEFT JOIN `update_collections` " . "ON `updates`.`collection_unified_resource_name` = `update_collections`.`unified_resource_name` " . "LEFT JOIN `publications` " . "ON (`publications`.`id` = `revision_requests`.`publication_id`) " . "WHERE `updates`.`revision_request_id` IS NULL " . "AND `publications`.`deleted_at` IS NULL " . "AND `publications`.`domain_unified_resource_name` = ? " . "AND `update_collections`.`publish_at` <= NOW() " . "AND `update_collections`.`publish_until` > NOW() " . "GROUP BY `revision_requests`.`publication_id` " . "ORDER BY `updated_at` DESC) " . "`publications` ORDER BY `updated_at` DESC"; $connection = NULL === $arg_connection ? Propel::getConnection(self::DATABASE_NAME) : $arg_connection; $statement = $connection->prepareStatement($sql); return self::populateObjects($statement->executeQuery(array(0 => $arg_domainUnifiedResourceName), ResultSet::FETCHMODE_NUM)); } }
81. How about changing these applications?
82. Is your complex application reaching its full potential?
83. Tonight 1. Context: complex applications 2. CQRS: why and how? 3. Event Sourcing to the rescue
84. Command Query Responsibility Segregation
85. Command Query Responsibility Segregation
86. CQRS? Did you mean cqrs
87. Read operations Write operations
88. Command Query Responsibility Segregation
89. You can apply it today!
90. Really Mike?
91. Step 1: separate your models
92. <?php ! class CustomerReadModel { private $id; private $name; private $address; private $gender; ! public function getName() { return $this->name; } public function getAddress() { return $this->address; } public function getGender() { return $this->gender; } }
93. <?php ! class Customer { private $id; private $name; private $address; private $gender; ! public function setName($name) { $this->name = $name; } public function setAddress($address) { $this->address = $address; } public function setGender($gender) { $this->gender = $gender; } }
94. So what?
95. You can now design them individually
96. You can now scale them independently
97. Step 2: model your commands
98. <?php ! class Customer { private $id; private $name; private $address; private $gender; ! private function __construct($customerId, $name, $gender, Address $address) { $this->id = $customerId; $this->name = $name; $this->gender = $gender; $this->address = $address; } static public function signUp($customerId, $name, $gender, Address $address) { return new Customer($customerId, $name, $gender, $address); } ! public function moveToNewLivingAddress(Address $newAddress) { $this->address = $newAddress; } }
99. <?php ! final class CustomerCommandHandler implements HandlesCommands { ! private $customers; ! public function __construct (CustomerRepository $aRepository) { $this->customers = $aRepository; } ! public function couldYou (Command $aCommand) { if ($aCommand instanceof PleaseSignCustomerUp) { $this->signUp($aCommand); } elseif ($aCommand instanceof PleaseMoveCustomerToNewLivingAddress) { $this->moveCustomerToNewLiving($aCommand); } else { // Intentionally empty: this will only happen during development. } } ! private function signUp (PleaseSignCustomerUp $aCommand) { $aCustomerId = $aCommand->customerId(); ! try { $aCustomer = $this->lockerServices->find($anEvent); // TODO: it exists, talk to the business how to deal with this } catch (SorryCustomerCouldNotBeFound $anException) { $aCustomer = Customer::signUp( $aCustomerId, $aCommand->name(), $aCommand->gender(), $aCommand->address() ); } ! $this->customers->add($aCustomer); } ! private function moveCustomerToNewLiving (PleaseMoveCustomerToNewLivingAddress $aCommand) { $aCustomerId = $aCommand->customerId(); $aCustomer = $this->customers->find($anEvent); ! $aCustomer->moveToNewLivingAddress($aCommand->address()); ! $this->lockerServices->add($aLockerService); } }
100. So what?
101. The interface is now revealing intention
102. You can make the user interface task-oriented
103. You are now aware of the intent of the user
104. Step 3: develop specific read-models
105. <?php ! /** * Publications are the contextual point for all other objects * * @author Marijn Huizendveld <marijn@debaasmedia.nl> * @version $Revision: 163 $ changed by $Author: buroknapzak $ * * @copyright De Baas Media (2010) */ class kluPublicationPeer extends BasekluPublicationPeer { /** * Select the publications that have recently been updated. * * @param string $arg_connection * * @return array */ static public function retrieveRecentlyUpdatedForDomain ($arg_domainUnifiedResourceName = NULL, $arg_connection = NULL) { $sql = "SELECT * FROM (SELECT `publications`.`id` AS ID " . ", `publications`.`name` AS NAME " . ", `publications`.`unified_resource_name` AS UNIFIED_RESOURCE_NAME " . ", `publications`.`domain_unified_resource_name` AS DOMAIN_UNIFIED_RESOURCE_NAME " . ", `publications`.`introduction` AS INTRODUCTION " . ", `publications`.`created_at` AS CREATED_AT " . ", MAX(`revision_requests`.`applied_at`) AS UPDATED_AT " . ", `publications`.`deleted_at` AS DELETED_AT " . "FROM `revision_requests` " . "LEFT JOIN `updates` " . "ON (`updates`.`id` = `revision_requests`.`update_id`) " . "LEFT JOIN `update_collections` " . "ON `updates`.`collection_unified_resource_name` = `update_collections`.`unified_resource_name` " . "LEFT JOIN `publications` " . "ON (`publications`.`id` = `revision_requests`.`publication_id`) " . "WHERE `updates`.`revision_request_id` IS NULL " . "AND `publications`.`deleted_at` IS NULL " . "AND `publications`.`domain_unified_resource_name` = ? " . "AND `update_collections`.`publish_at` <= NOW() " . "AND `update_collections`.`publish_until` > NOW() " . "GROUP BY `revision_requests`.`publication_id` " . "ORDER BY `updated_at` DESC) " . "`publications` ORDER BY `updated_at` DESC"; $connection = NULL === $arg_connection ? Propel::getConnection(self::DATABASE_NAME) : $arg_connection; $statement = $connection->prepareStatement($sql); return self::populateObjects($statement->executeQuery(array(0 => $arg_domainUnifiedResourceName), ResultSet::FETCHMODE_NUM)); } }
106. <?php ! /** * Publications are the contextual point for all other objects * * @author Marijn Huizendveld <marijn@debaasmedia.nl> * @version $Revision: 163 $ changed by $Author: buroknapzak $ * * @copyright De Baas Media (2010) */ class kluPublicationPeer extends BasekluPublicationPeer { /** * Select the publications that have recently been updated. * * @param string $arg_connection * * @return array */ static public function retrieveRecentlyUpdatedForDomain ($arg_domainUnifiedResourceName = NULL, $arg_connection = NULL) { $sql = "SELECT * FROM recently_updated WHERE domain = ? ORDER BY `updated_at` DESC"; $connection = NULL === $arg_connection ? Propel::getConnection(self::DATABASE_NAME) : $arg_connection; $statement = $connection->prepareStatement($sql); return self::populateObjects($statement->executeQuery(array(0 => $arg_domainUnifiedResourceName), ResultSet::FETCHMODE_NUM)); } }
107. So what?
108. You’ve reduced the cognitive load for this piece of code
109. You can improve performance by pre-calculating results
110. Tonight 1. Context: complex applications 2. CQRS: why and how? 3. Event Sourcing to the rescue
111. By now you’re modeling it right
112. Expressive domain model
113. Intuitive interfaces
114. Model is contextual and expressive
115. But data is still continuously lost…
116. and reporting is not yet easy.
117. If only we could track the intent of changes…
118. and respond to those changes accordingly.
119. Well we can
120. – Greg Young “(…) storing current state as a series of events and rebuilding state within the system by replaying that series of events.”
121. Step 1: Extract business events
122. Something that happened in the past of interest to the business
123. They are immutable: something that happened cannot be undone.
124. <?php ! final class BasketWasPickedUp implements DomainEvent { private $basketId; ! public function __construct($basketId) { $this->basketId = (string) $basketId; } ! public function getAggregateId() { return $this->basketId; } }
125. So what?
126. You’ve created a shared understanding with the business
127. Step 2: Record and dispatch them
128. <?php ! final class Basket implements RecordsEvents { public static function pickUp(BasketId $basketId) { $basket = new BasketV2(); ! $basket->recordThat( new BasketWasPickedUp($basketId) ); ! return $basket; } protected function ackwnoledgesBasketWasPickedUp(BasketWasPickedUp $anEvent) { $this->basketId = $anEvent->basketId(); } ! private $basketId; private $latestRecordedEvents = []; private function __construct(BasketId $basketId) { // private constructor } ! private function recordThat(DomainEvent $domainEvent) { $this->latestRecordedEvents[] = $domainEvent; $this->ackwnoledge($domainEvent); } ! private function ackwnoledge(DomainEvent $event) { $method = 'ackwnoledge' . $event->name(); ! $this->$method($event); } ! public function getRecordedEvents() { return new DomainEvents($this->latestRecordedEvents); } ! public function clearRecordedEvents() { $this->latestRecordedEvents = []; } }
129. So what?
130. You’re now keeping track of the history of the business
131. Step 3: React to them
132. <?php ! final class DebriefingOutboxEntryProjector { ! private $entries; ! public function __construct (DebriefingOutboxEntryRepository $aRepository) { $this->entries = $aRepository; } ! /** * @param \Hank\Event $anEvent * * @throws \Entropt\LockerControl\DebriefingOutboxEntry\SorryDebriefingOutboxEntryCouldNotBePersisted */ public function project (DomainEvent $anEvent) { if ($anEvent instanceof DebriefCouldNotBeSent) { $this->debriefCouldNotBeSent($anEvent); } elseif ($anEvent instanceof DebriefWasSent) { $this->debriefWasSent($anEvent); } else { // intentionally empty: we don't want to break any long running processes } } ! private function debriefCouldNotBeSent (DebriefCouldNotBeSent $anEvent) { $this->entries->add(new DebriefingOutboxEntry(new Event($anEvent->event(), $anEvent->day()))); } ! private function debriefWasSent (DebriefWasSent $anEvent) { $aReference = new Event($anEvent->event(), $anEvent->day()); ! try { $anOnGoingEvent = $this->entries->find($aReference); ! $this->entries->remove($anOnGoingEvent); } catch (SorryDebriefingOutboxEntryCouldNotBeFound $anException) { // intentionally empty: we wanted to remove it, if it's not there than we just move on. } } }
133. So what?
134. You can now easily hook into the business processes
135. You can project the information in the events in any way desired
136. You replay history whenever you gain new insights
137. Step 4: Simplify your tests
138. // Nothing happens ! $scenario->given($aPreCondition) // events ->andGiven($anotherPreCondition) ->when($aCommand) // commands ->thenNothingShouldHaveHappened();
139. // Something happens ! $scenario->given($aPreCondition) // events ->andGiven($anotherPreCondition) ->when($aCommand) // commands ->then($anOutcome) // events ->andThen($anotherOutcome) ->butNothingElseShouldHaveHappened();
140. // Exception occurs ! $scenario->given($aPreCondition) // events ->andGiven($anotherPreCondition) ->when($aCommand) // commands ->thenWeAreSorry($anError); // exception
141. // Process triggered ! $scenario->given($aPreCondition) // events ->andGiven($anotherPreCondition) ->when($aTrigger) // event ->then($aProcess) // command ->butNothingElse();
142. // Input ignored ! $scenario->given($aPreCondition) // events ->andGiven($anotherPreCondition) ->when($aTrigger) // event ->thenNothingShouldHaveHappened();
143. // Projection triggered ! $scenario->given($aPreCondition) // events ->andGiven($anotherPreCondition) ->when($aTrigger) // event ->then($aProjection) // read-model ->butNothingElse();
144. // Input ignored ! $scenario->given($aPreCondition) // events ->andGiven($anotherPreCondition) ->when($aTrigger) // event ->thenNothingShouldHaveHappened();
145. <?php ! final class PleaseMakeLockersAvailableForRentTest extends CommandHandlerTestCase { ! /** * @test * @dataProvider ProvideNameOfEventDayOfEventNameOfLockerHostAndListOfAvailableLockers::that_are_not_nil */ public function makes_lockers_available_for_rent ( NameOfEvent $aName, DayOfEvent $aDay, NameOfLockerHost $aHost, UniqueLockerNumbers $aListOfAvailableLockers ) { $this->testScenarioThat ->when(PleaseMakeLockersAvailableForRent::v1($aName, $aDay, TimeOfCommand::rightNow(), $aHost, $aListOfAvailableLockers)) ! ->then(LockersWereMadeAvailableForRent::v1($aName, $aDay, TimeOfEvent::rightNow(), $aHost, $aListOfAvailableLockers)) ->butNothingElseShouldHaveHappened(); } ! /** * @test * @dataProvider ProvideNameOfEventDayOfEventNameOfLockerHostAndListOfAvailableLockers::that_are_not_nil */ public function ignores_command_when_an_event_with_identical_name_already_exists ( NameOfEvent $aName, DayOfEvent $aDay, NameOfLockerHost $aHost, UniqueLockerNumbers $aListOfAvailableLockers ) { $this->testScenarioThat ->given(LockersWereMadeAvailableForRent::v1($aName, $aDay, TimeOfEvent::fromString('Thursday March 6th 2014, 12:44:20 UTC'))) ! ->when(PleaseMakeLockersAvailableForRent::v1($aName, $aDay, TimeOfCommand::rightNow(), $aHost, $aListOfAvailableLockers)) ! ->thenNothingShouldHaveHappened(); } }
146. So what?
147. You’re domain expert now understands your tests
148. You can visualize the system to improve communication
149. When should you apply this?
150. Is your application complex enough for CQRS?
151. Is your application simple enough for CRUD?
152. Questions?
153. People @mathiasverraes @beberlei @rosstuck @iam_asm89
154. Resources • http://cqrs.files.wordpress.com/2010/11/cqrs_documents.pdf • http://codebetter.com/gregyoung/2010/02/16/cqrs-task-based-uis-event-sourcing-agh/ • http://martinfowler.com/bliki/CQRS.html • http://www.viddler.com/v/dc528842