TOTAL RECALL - The application that never forgets

Building an application upon CQRS and Event Sourcing offers three pretty nice benefits.

1. Well structured code and business logic, separated by read and write concerns.
2. The source of truth - A reliable and recoverable view into the past of your application state.
3. The opportunity to answer future questions that you don't know about today.

This talk explains the good fit of two combined application architecture approaches applied to a well known real world example. It shows how to tackle some pitfalls, gives practical advices on infrastructure and exemplifies the aforementioned benefits.

This talk was given at the PHP Central Europe 2018 Conference in Prague, Czech Republic.

Transcript

1. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
   1
   THE APPLICATION THAT NEVER FORGETS
   

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2. HOLGER WOLTERSDORF
   CIO • FATHER • PHP DEV WITH ♥ • MARKDOWN LOVER
   github.com/hollodotme
   @hollodotme
   

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3. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
   3
   CQRS + EVENT SOURCING
   

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4. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
   4
   CQRS
   (COMMAND QUERY RESPONSIBILITY SEGREGATION)
   

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5. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
   CQS => CQRS
   5
   ๏ CQRS EVOLVED FROM THE CQS IMPLEMENTATION PATTERN
   ๏ First stated by Bertrand Meyer in the 1990’s 

   when working on the Eiffel programming language

   ๏ Describes a semantic implementation pattern for object methods
   ๏ Queries: return results, but do not change the observable state (free of side effects)
   ๏ Commands: change the state of objects, but do not return values
   Bertrand Meyer
   

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6. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
   CQS => CQRS
   6
   class Number
   {
   /** @var int */
   private $number = 0;
   public function getIncrementedNumber() : int
   {
   $this->number++;
   return $this->number;
   }
   }
   BAD
   

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7. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
   CQS => CQRS
   7
   class Number
   {
   /** @var int */
   private $number = 0;
   public function increment() : void # Command
   {
   $this->number++;
   }
   public function getNumber() : int # Query
   {
   return $this->number;
   }
   }
   GOOD
   

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8. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
   CQS => CQRS
   8
   ๏ CQRS IS AN ARCHITECTURE PATTERN
   ๏ Described by Greg Young’s CQRS documents in 2010
   ๏ One part is responsible to change the state of the application
   ๏ One part is responsible to represent the current state of the application
   ๏ Command and Query have a broader semantic meaning than in CQS
   ๏ Key concept is to split your application into:
   ๏ A write side that is able to process commands (write-only)
   ๏ A read side that is able to answer queries (read-only)
   ๏ Give each side an appropriate storage
   GREG YOUNG
   

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9. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
   9
   APPLICATION?
   

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10. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    10
    WEB APPLICATION LAYERS
    REQUEST HANDLING LAYER
    BUSINESS LOGIC LAYER
    PERSISTENCE LAYER
    

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11. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    11
    WEB APPLICATION LAYERS
    REQUEST HANDLING LAYER
    BUSINESS LOGIC LAYER
    PERSISTENCE LAYER
    KNOWS
    HTTP
    

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12. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    12
    WEB APPLICATION LAYERS
    REQUEST HANDLING LAYER
    BUSINESS LOGIC LAYER
    PERSISTENCE LAYER
    KNOWS
    HTTP
    KNOWS
    BUSINESS
    RULES
    

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13. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    13
    WEB APPLICATION LAYERS
    REQUEST HANDLING LAYER
    BUSINESS LOGIC LAYER
    PERSISTENCE LAYER
    KNOWS
    HTTP
    KNOWS
    BUSINESS
    RULES
    KNOWS
    DATABASE
    

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14. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    14
    WEB APPLICATION LAYERS
    REQUEST HANDLING LAYER
    BUSINESS LOGIC LAYER
    PERSISTENCE LAYER
    CQRS CAN BE APPLIED TO ALL OF THEM
    KNOWS
    HTTP
    KNOWS
    BUSINESS
    RULES
    KNOWS
    DATABASE
    

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15. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    15
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    AFTER CQRS WAS APPLIED
    VIEW LOGIC
    

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16. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    16
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    HOW DO WE GET FROM HERE… … TO THERE?
    VIEW LOGIC
    

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17. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    17
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    PUBLISH SUBSCRIBE
    REDIRECT (+ SESSION)
    VIEW LOGIC
    

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18. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    REPRESENTATION
    18
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    VIEW LOGIC
    PUBLISH SUBSCRIBE
    REDIRECT (+ SESSION)
    REPRESENTATION
    MESSAGE
    BROKER
    ASYNC
    EVENTUAL
    CONSISTENCY
    !
    

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19. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    REPRESENTATION
    19
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    VIEW LOGIC
    PUBLISH SUBSCRIBE
    REDIRECT (+ SESSION)
    REPRESENTATION
    PHP FASTCGI
    CLIENT
    ASYNC
    EVENTUAL
    CONSISTENCY
    !
    

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20. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    REPRESENTATION
    20
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    VIEW LOGIC
    PUBLISH SUBSCRIBE
    REPRESENTATION
    MESSAGE
    BROKER
    

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21. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    REPRESENTATION
    21
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    VIEW LOGIC
    PUBLISH SUBSCRIBE
    REPRESENTATION
    MESSAGE
    BROKER
    

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22. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    REPRESENTATION
    22
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    VIEW LOGIC
    PUBLISH SUBSCRIBE
    REPRESENTATION
    MESSAGE
    BROKER
    

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23. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    23
    CQRS (REQUEST HANDLING LAYER)
    ๏ GET-REQUEST
    ๏ NO VIEW LOGIC
    ๏ COULD BE A STATIC

    HTML PAGE
    ๏ SUBMIT TRIGGERS

    POST REQUEST
    

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24. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    24
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    REDIRECT (+ SESSION)
    VIEW LOGIC
    POST GET
    x
    » ERRORS »
    

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25. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    25
    CQRS (REQUEST HANDLING LAYER)
    ๏ GET-REQUEST 

    AFTER REDIRECT
    ๏ CHECK FOR ERRORS 

    IN SESSION
    ๏ ERRORS RENDERED
    INTO VIEW
    ๏ ONLY SUBMIT 

    TRIGGERS POST
    REQUEST
    ๏ RELOAD DOESN’T
    

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26. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    26
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    VIEW LOGIC
    GET
    

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27. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    27
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    VIEW LOGIC
    GET GET GET GET
    

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28. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    READ-/WRITE-REQUESTS
    28
    5 %
    95 %
    Reads Writes
    FOR A FASHION
    ONLINE SHOP
    

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29. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (REQUEST HANDLING LAYER)
    29
    final class NewsletterSubscriptionValidator implements MiddlewareInterface
    {
    /** @var ValidatorInterface !*/
    private $validator;
    /** @var SessionInterface !*/
    private $session;
    public function !__construct( ValidatorInterface $validator, SessionInterface $session )
    {
    $this!->validator = $validator;
    $this!->session = $session;
    }
    public function process( ServerRequestInterface $request, RequestHandlerInterface $handler ) : ResponseInterface
    {
    $this!->validator!->checkUserInput( $request );
    if ( $this!->validator!->failed() )
    {
    $this!->session!->addErrors(
    'initSubscription',
    $this!->validator!->getErrors()
    );
    return Redirect!::to( '/subscription-form' );
    }
    return $handler!->handle( $request );
    }
    }
    

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30. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (REQUEST HANDLING LAYER)
    30
    final class NewsletterSubscriptionForm implements MiddlewareInterface
    {
    /** @var SessionInterface !*/
    private $session;
    public function !__construct( SessionInterface $session )
    {
    $this!->session = $session;
    }
    public function process( ServerRequestInterface $request, RequestHandlerInterface $handler ) : ResponseInterface
    {
    return Page!::fromTemplate( 'subscription-form' )
    !->withErrors( $this!->session!->getErrors( 'initSubscription' ) );
    }
    }
    

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31. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    31
    CQRS (REQUEST HANDLING LAYER)
    ๏ GET-REQUEST
    ๏ NO VIEW LOGIC
    ๏ COULD BE A STATIC

    HTML PAGE
    ๏ CAN BE DELETED 

    AFTER SUBSCRIPTION

    IS FINISHED
    

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32. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (REQUEST HANDLING LAYER)
    32
    final class SubscriptionInitializer implements MiddlewareInterface
    {
    /** @var InitSubscriptionCommandHandler !*/
    private $commandHandler;
    /** @var MessageBrokerInterface !*/
    private $messageBroker;
    public function !__construct( InitSubscriptionCommandHandler $commandHandler, MessageBrokerInterface $messageBroker )
    {
    $this!->commandHandler = $commandHandler;
    $this!->messageBroker = $messageBroker;
    }
    public function process( ServerRequestInterface $request, RequestHandlerInterface $handler ) : ResponseInterface
    {
    $command = InitSubscriptionCommand!::withFullNameAndEmail(
    Fullname!::fromString( $request!->getParsedBody()['fullName'] ),
    Email!::fromString( $request!->getParsedBody()['email'] )
    );
    $result = $this!->commandHandler!->handle( $command );
    $message = SubscriptionInitialized!::withSubscription( $result!->getSubscription() );
    $this!->messageBroker!->publish( $message );
    return Redirect!::to( '/thanks-' . $result!->getSubscription()!->getId() . '.html' );
    }
    }
    

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33. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (REQUEST HANDLING LAYER)
    33
    final class SubscriptionInitializer implements MiddlewareInterface
    {
    /** @var InitSubscriptionCommandHandler !*/
    private $commandHandler;
    /** @var MessageBrokerInterface !*/
    private $messageBroker;
    public function !__construct( InitSubscriptionCommandHandler $commandHandler, MessageBrokerInterface $messageBroker )
    {
    $this!->commandHandler = $commandHandler;
    $this!->messageBroker = $messageBroker;
    }
    public function process( ServerRequestInterface $request, RequestHandlerInterface $handler ) : ResponseInterface
    {
    $command = InitSubscriptionCommand!::withFullNameAndEmail(
    Fullname!::fromString( $request!->getParsedBody()['fullName'] ),
    Email!::fromString( $request!->getParsedBody()['email'] )
    );
    $result = $this!->commandHandler!->handle( $command );
    $message = SubscriptionInitialized!::withSubscription( $result!->getSubscription() );
    $this!->messageBroker!->publish( $message );
    return Redirect!::to( '/thanks-' . $result!->getSubscription()!->getId() . '.html' );
    }
    }
    ENTERING BUSINESS LOGIC LAYER
    & CHANGING STATE
    

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34. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (REQUEST HANDLING LAYER)
    34
    final class SubscriptionInitializer implements MiddlewareInterface
    {
    /** @var InitSubscriptionCommandHandler !*/
    private $commandHandler;
    /** @var MessageBrokerInterface !*/
    private $messageBroker;
    public function !__construct( InitSubscriptionCommandHandler $commandHandler, MessageBrokerInterface $messageBroker )
    {
    $this!->commandHandler = $commandHandler;
    $this!->messageBroker = $messageBroker;
    }
    public function process( ServerRequestInterface $request, RequestHandlerInterface $handler ) : ResponseInterface
    {
    $command = InitSubscriptionCommand!::withFullNameAndEmail(
    Fullname!::fromString( $request!->getParsedBody()['fullName'] ),
    Email!::fromString( $request!->getParsedBody()['email'] )
    );
    $result = $this!->commandHandler!->handle( $command );
    $message = SubscriptionInitialized!::withSubscription( $result!->getSubscription() );
    $this!->messageBroker!->publish( $message );
    return Redirect!::to( '/thanks-' . $result!->getSubscription()!->getId() . '.html' );
    }
    }
    TRIGGER NEW READ REPRESENTATION
    

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35. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    REPRESENTATION
    35
    WEB APPLICATION LAYERS
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    VIEW LOGIC
    PUBLISH SUBSCRIBE
    REPRESENTATION
    MESSAGE
    BROKER
    

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36. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (BUSINESS LOGIC)
    36
    final class InitSubscriptionCommand
    {
    /** @var FullName !*/
    private $fullName;
    /** @var Email !*/
    private $email;
    private function !__construct( FullName $fullName, Email $email )
    {
    $this!->fullName = $fullName;
    $this!->email = $email;
    }
    public static function withFullNameAndEmail( FullName $fullName, Email $email ) : self
    {
    return new self( $fullName, $email );
    }
    public function getFullName() : FullName
    {
    return $this!->fullName;
    }
    public function getEmail() : Email
    {
    return $this!->email;
    }
    }
    

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37. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (BUSINESS LOGIC)
    37
    final class InitSubscriptionCommandHandler
    {
    /** @var SubscriptionRepository !*/
    private $repository;
    public function !__construct( SubscriptionRepository $repository )
    {
    $this!->repository = $repository;
    }
    public function handle( InitSubscriptionCommand $command ) : InitSubscriptionResult
    {
    try
    {
    $subscription = Subscription!::fromIdFullNameAndEmail(
    SubscriptionId!::generate(),
    $command!->getFullName(),
    $command!->getEmail()
    );
    $this!->repository!->add( $subscription );
    return InitSubscriptionResult!::withSubscription( $subscription );
    }
    catch ( Throwable $e )
    {
    return InitSubscriptionResult!::withErrorMessage( $e!->getMessage() );
    }
    }
    }
    

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38. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (BUSINESS LOGIC)
    38
    final class InitSubscriptionResult
    {
    /** @var bool !*/
    private $succeeded = false;
    /** @var string !*/
    private $errorMessage = '';
    /** @var Subscription !*/
    private $subscription;
    public static function withSubscription( Subscription $subscription ) : self
    {
    $result = new self();
    $result!->succeeded = true;
    $result!->subscription = $subscription;
    return $result;
    }
    public static function withErrorMessage( string $errorMessage ) : self
    {
    $result = new self();
    $result!->errorMessage = $errorMessage;
    return $result;
    }
    }
    

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39. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (PRESENTATION)
    39
    final class SubscriptionInitializedSubscriber
    {
    public function notify( SubscriptionInitialized $message ) : void
    {
    $subscription = $message!->getSubscription();
    Page!::fromTemplate( 'thanks' )
    !->withData( ['subscription' !=> $subscription] )
    !->saveAsHtml( '/thanks-' . $subscription!->getId() . '.html' );
    }
    }
    final class SendConfirmationMailSubscriber
    {
    public function notify( SubscriptionInitialized $message ) : void
    {
    $subscription = $message!->getSubscription();
    Email!::fromTemplate( 'confirm-subscription' )
    !->withData( ['subscription' !=> $subscription] )
    !->to( $subscription!->getEmail() )
    !->send();
    }
    }
    

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40. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    40
    CQRS (REQUEST HANDLING LAYER)
    ๏ E-MAIL
    ๏ CALL TO ACTION

    FOR A STATE CHANGE
    ๏ POST REQUESTS

    NOT AVAILABLE 

    FROM E-MAILS!
    

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41. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    41
    RESPECT HTTP VERBS!
    CQRS (REQUEST HANDLING LAYER)
    

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42. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    42
    […] the convention has been established
    that the GET and HEAD methods
    SHOULD NOT have the significance
    of taking an action other than retrieval.
    These methods ought
    to be considered "safe".
    https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html
    CQRS (REQUEST HANDLING LAYER)
    

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43. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    43
    CQRS (REQUEST HANDLING LAYER)
    ๏ DON’T CHANGE STATE 

    BY READ REQUESTS!
    ๏ GET-REQUEST
    ๏ NO VIEW LOGIC
    ๏ COULD BE A STATIC

    HTML PAGE, PREPARED
    BASED ON SUCCESSFUL 

    INIT RESULT
    ๏ SUBMIT TRIGGERS 

    POST REQUEST
    ๏ CAN BE DELETED 

    AFTER SUBSCRIPTION

    IS FINISHED
    

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44. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    44
    CQRS (REQUEST HANDLING LAYER)
    ๏ GET-REQUEST

    AFTER REDIRECT
    ๏ NO VIEW LOGIC
    ๏ COULD BE A STATIC

    HTML PAGE, PREPARED
    BASED ON SUCCESSFUL 

    FINISH RESULT
    

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45. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    45
    PERSISTENCE LAYER & STATE
    SubscriberID Fullname Email Interval Subscribed Confirmed Unsubscribed
    ‹UUID-HW›
    Holger
    Woltersdorf
    hollodotme
    @PHPkonf.org
    ONLY WHEN
    PHPCE
    happens
    2018-05-19 2018-05-20 2018-05-21
    ‹UUID-JD› Jane Doe jane@doe.com Monthly 2018-03-01 NULL NULL
    SubscriberID Topic
    ‹UUID-HW› HIPSTER JEANS
    ‹UUID-HW› NERD CAPS
    ‹UUID-HW› MEME SHIRTS
    

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46. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    46
    PERSISTENCE LAYER & STATE
    WHAT HAPPENS, IF…
    I subscribe again
    for MEME SHIRTS only
    with WEEKLY interval
    

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47. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    47
    PERSISTENCE LAYER & STATE
    SubscriberID Fullname Email Interval Subscribed Confirmed Unsubscribed
    ‹UUID-HW›
    Holger
    Woltersdorf
    hollodotme
    @PHPkonf.org
    Weekly 2018-05-22 2018-05-23 NULL
    ‹UUID-JD› Jane Doe jane@doe.com Monthly 2018-03-01 NULL NULL
    SubscriberID Topic
    ‹UUID-HW› MEME SHIRTS
    

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48. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    48
    PERSISTENCE LAYER & STATE
    WORKS, RIGHT?
    

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49. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    49
    PERSISTENCE LAYER & STATE
    …
    SINCERLY,
    YOUR
    BUSINESS
    DATA
    ANALYST
    

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50. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (PERSISTENCE LAYER - STATE)
    50
    What have we lost?
    ACTUALLY ALL INFORMATION
    ABOUT THE FIRST SUBSCRIPTION
    except e-mail & full name
    

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51. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS (PERSISTENCE LAYER - STATE)
    51
    What else have we lost?
    ANALYSABLE DATA
    ABOUT THE USER’S DECISION
    TO REACTIVATE AND CHANGE SUBSCRIPTION
    

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52. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    52
    CQRS (PERSISTENCE LAYER - STATE)
    The application state is observable,
    BUT ONLY AT THE EXACT POINT OF TIME
    we look at it.
    

    View Slide

53. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    53
    + EVENT SOURCING
    

    View Slide

54. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING
    54
    ๏ EVENT SOURCING IS AN ANALYSIS PATTERN
    ๏ Article by Martin Fowler in 2005
    ๏ CQRS + Event Sourcing also part of Greg Young’s CQRS documents
    ๏ Pattern was already used in accounting software way earlier
    ๏ Key concept: 

    

    "Record all changes to application state as a sequence of events."

    — Martin Fowler
    GREG YOUNG
    MARTIN FOWLER
    

    View Slide

55. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    55
    INSTALLING EVENT SOURCING
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    PUBLISH SUBSCRIBE
    REDIRECT (+ SESSION)
    VIEW LOGIC
    

    View Slide

56. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    56
    INSTALLING EVENT SOURCING
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    STATE
    PUBLISH SUBSCRIBE
    REDIRECT (+ SESSION)
    VIEW LOGIC
    

    View Slide

57. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    57
    INSTALLING EVENT SOURCING
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    EVENT STORE
    PUBLISH SUBSCRIBE
    REDIRECT (+ SESSION)
    VIEW LOGIC
    READ HISTORY OF CHANGES
    RECORD NEW CHANGES
    

    View Slide

58. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING
    58
    BUSINESS ENTITY
    EVENTSTORE
    COMMAND
    TRIGGER CHANGES
    EMITS EVENTS
    (ALL NEW CHANGES)
    BUILT FROM
    EVENT STREAM
    (HISTORY OF CHANGES)
    PUBLISH NEWLY RECORDED EVENTS
    

    View Slide

59. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    59
    EVENT STORE
    Seq StreamType StreamID StreamSeq EventID Payload Occurred MetaX Meta…
    10
    Newsletter

    Subscription
    ‹UUID-HW› 1
    Subscription was
    initiated
    {"json"}
    2017-05-21
    T12:13:14
    SHOP TY …
    11 Newsletter

    Subscription
    ‹UUID-HW› 2 Interval was
    changed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    12 Newsletter

    Subscription
    ‹UUID-HW› 3 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    13 Newsletter
    Subscription
    ‹UUID-HW› 4 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    14 Newsletter

    Subscription
    ‹UUID-HW› 5 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    15 Newsletter

    Subscription
    ‹UUID-HW› 6 Subscription was
    confirmed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    33 Newsletter

    Subscription
    ‹UUID-HW› 7 Subscription was
    canceled
    {"json"} 2017-05-25
    T07:09:09
    SHOP DE …
    50 Newsletter

    Subscription
    ‹UUID-HW› 8 Subscription was
    reactivated
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    51 Newsletter

    Subscription
    ‹UUID-HW› 9 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    52 Newsletter
    Subscription
    ‹UUID-HW› 10 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    53 Newsletter

    Subscription
    ‹UUID-HW› 11 Interval was
    changed
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    54 Newsletter

    Subscription
    ‹UUID-HW› 12 Subscription was
    confirmed
    {"json"} 2017-06-02
    T16:17:18
    SHOP DE …
    

    View Slide

60. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    Seq StreamType StreamID StreamSeq EventID Payload Occurred MetaX Meta…
    10
    Newsletter

    Subscription
    ‹UUID-HW› 1
    Subscription was
    initiated
    {"json"}
    2017-05-21
    T12:13:14
    SHOP TY …
    11 Newsletter

    Subscription
    ‹UUID-HW› 2 Interval was
    changed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    12 Newsletter

    Subscription
    ‹UUID-HW› 3 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    13 Newsletter
    Subscription
    ‹UUID-HW› 4 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    14 Newsletter

    Subscription
    ‹UUID-HW› 5 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    15 Newsletter

    Subscription
    ‹UUID-HW› 6 Subscription was
    confirmed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    33 Newsletter

    Subscription
    ‹UUID-HW› 7 Subscription was
    canceled
    {"json"} 2017-05-25
    T07:09:09
    SHOP DE …
    50 Newsletter

    Subscription
    ‹UUID-HW› 8 Subscription was
    reactivated
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    51 Newsletter

    Subscription
    ‹UUID-HW› 9 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    52 Newsletter
    Subscription
    ‹UUID-HW› 10 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    53 Newsletter

    Subscription
    ‹UUID-HW› 11 Interval was
    changed
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    54 Newsletter

    Subscription
    ‹UUID-HW› 12 Subscription was
    confirmed
    {"json"} 2017-06-02
    T16:17:18
    SHOP DE …
    60
    EVENT STORE
    SEQUENCE SORTING ALL EVENTS IN THE EVENT STORE
    (AUTO-INCREMENT)
    

    View Slide

61. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    Seq StreamType StreamID StreamSeq EventID Payload Occurred MetaX Meta…
    10
    Newsletter

    Subscription
    ‹UUID-HW› 1
    Subscription was
    initiated
    {"json"}
    2017-05-21
    T12:13:14
    SHOP TY …
    11 Newsletter

    Subscription
    ‹UUID-HW› 2 Interval was
    changed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    12 Newsletter

    Subscription
    ‹UUID-HW› 3 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    13 Newsletter
    Subscription
    ‹UUID-HW› 4 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    14 Newsletter

    Subscription
    ‹UUID-HW› 5 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    15 Newsletter

    Subscription
    ‹UUID-HW› 6 Subscription was
    confirmed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    33 Newsletter

    Subscription
    ‹UUID-HW› 7 Subscription was
    canceled
    {"json"} 2017-05-25
    T07:09:09
    SHOP DE …
    50 Newsletter

    Subscription
    ‹UUID-HW› 8 Subscription was
    reactivated
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    51 Newsletter

    Subscription
    ‹UUID-HW› 9 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    52 Newsletter
    Subscription
    ‹UUID-HW› 10 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    53 Newsletter

    Subscription
    ‹UUID-HW› 11 Interval was
    changed
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    54 Newsletter

    Subscription
    ‹UUID-HW› 12 Subscription was
    confirmed
    {"json"} 2017-06-02
    T16:17:18
    SHOP DE …
    61
    EVENT STORE
    StreamType
    NAME OF THE BUSINESS ENTITY
    StreamID
    UNIQUE ID OF SPECIFIC BUSINESS ENTITY
    StreamSeq
    VERSION OF THE SPECIFIC BUSINESS ENTITY INSTANCE
    (USED TO SORT THE ENTITY’S EVENT STREAM)
    

    View Slide

62. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    Seq StreamType StreamID StreamSeq EventID Payload Occurred MetaX Meta…
    10
    Newsletter

    Subscription
    ‹UUID-HW› 1
    Subscription was
    initiated
    {"json"}
    2017-05-21
    T12:13:14
    SHOP TY …
    11 Newsletter

    Subscription
    ‹UUID-HW› 2 Interval was
    changed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    12 Newsletter

    Subscription
    ‹UUID-HW› 3 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    13 Newsletter
    Subscription
    ‹UUID-HW› 4 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    14 Newsletter

    Subscription
    ‹UUID-HW› 5 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    15 Newsletter

    Subscription
    ‹UUID-HW› 6 Subscription was
    confirmed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    33 Newsletter

    Subscription
    ‹UUID-HW› 7 Subscription was
    canceled
    {"json"} 2017-05-25
    T07:09:09
    SHOP DE …
    50 Newsletter

    Subscription
    ‹UUID-HW› 8 Subscription was
    reactivated
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    51 Newsletter

    Subscription
    ‹UUID-HW› 9 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    52 Newsletter
    Subscription
    ‹UUID-HW› 10 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    53 Newsletter

    Subscription
    ‹UUID-HW› 11 Interval was
    changed
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    54 Newsletter

    Subscription
    ‹UUID-HW› 12 Subscription was
    confirmed
    {"json"} 2017-06-02
    T16:17:18
    SHOP DE …
    62
    EVENT STORE
    EventID
    NAME OF THE CHANGE
    (USED TO IDENTIFY EVENT CLASS)
    Payload
    ALL RELEVANT DATA THAT IS NEEDED
    TO REPRODUCE THE CHANGE
    USE ONE TECHNOLOGY INDEPENDENT
    DATA FORMAT!
    Occurred
    TIMESTAMP WHEN THE CHANGE WAS
    RECORDED
    DO NOT USE THIS FOR SORTING
    EVENT STREAMS
    DO NOT RELY ON TIMESTAMPS!
    IT’S JUST META DATA
    

    View Slide

63. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    Seq StreamType StreamID StreamSeq EventID Payload Occurred MetaX Meta…
    10
    Newsletter

    Subscription
    ‹UUID-HW› 1
    Subscription was
    initiated
    {"json"}
    2017-05-21
    T12:13:14
    SHOP TY …
    11 Newsletter

    Subscription
    ‹UUID-HW› 2 Interval was
    changed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    12 Newsletter

    Subscription
    ‹UUID-HW› 3 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    13 Newsletter
    Subscription
    ‹UUID-HW› 4 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    14 Newsletter

    Subscription
    ‹UUID-HW› 5 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    15 Newsletter

    Subscription
    ‹UUID-HW› 6 Subscription was
    confirmed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    33 Newsletter

    Subscription
    ‹UUID-HW› 7 Subscription was
    canceled
    {"json"} 2017-05-25
    T07:09:09
    SHOP DE …
    50 Newsletter

    Subscription
    ‹UUID-HW› 8 Subscription was
    reactivated
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    51 Newsletter

    Subscription
    ‹UUID-HW› 9 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    52 Newsletter
    Subscription
    ‹UUID-HW› 10 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    53 Newsletter

    Subscription
    ‹UUID-HW› 11 Interval was
    changed
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    54 Newsletter

    Subscription
    ‹UUID-HW› 12 Subscription was
    confirmed
    {"json"} 2017-06-02
    T16:17:18
    SHOP DE …
    63
    EVENT STORE
    ADDITIONAL META DATA
    BUSINESS IRRELEVANT
    DEPENDS ON YOUR DOMAIN
    AND INFRASTRUCTURE
    FOR EXAMPLE
    SHOP INSTANCE
    SERVER INSTANCE
    AUTH-USER (IF NOT BUSINESS RELEVANT)
    APPLICATION VERSION
    ETC.
    ADD WHATEVER YOU NEED
    

    View Slide

64. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    Seq StreamType StreamID StreamSeq EventID Payload Occurred MetaX Meta…
    10
    Newsletter

    Subscription
    ‹UUID-HW› 1
    Subscription was
    initiated
    {"json"}
    2017-05-21
    T12:13:14
    SHOP TY …
    11 Newsletter

    Subscription
    ‹UUID-HW› 2 Interval was
    changed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    12 Newsletter

    Subscription
    ‹UUID-HW› 3 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    13 Newsletter
    Subscription
    ‹UUID-HW› 4 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    14 Newsletter

    Subscription
    ‹UUID-HW› 5 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    15 Newsletter

    Subscription
    ‹UUID-HW› 6 Subscription was
    confirmed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    33 Newsletter

    Subscription
    ‹UUID-HW› 7 Subscription was
    canceled
    {"json"} 2017-05-25
    T07:09:09
    SHOP DE …
    50 Newsletter

    Subscription
    ‹UUID-HW› 8 Subscription was
    reactivated
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    51 Newsletter

    Subscription
    ‹UUID-HW› 9 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    52 Newsletter
    Subscription
    ‹UUID-HW› 10 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    53 Newsletter

    Subscription
    ‹UUID-HW› 11 Interval was
    changed
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    54 Newsletter

    Subscription
    ‹UUID-HW› 12 Subscription was
    confirmed
    {"json"} 2017-06-02
    T16:17:18
    SHOP DE …
    64
    EVENT STORE
    FIRST SUBSCRIPTION
    PLEASE NOTE:
    GIVING BIRTH TO A NEW BUSINESS ENTITY
    IS A CHANGE TO APPLICATION STATE
    

    View Slide

65. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    Seq StreamType StreamID StreamSeq EventID Payload Occurred MetaX Meta…
    10
    Newsletter

    Subscription
    ‹UUID-HW› 1
    Subscription was
    initiated
    {"json"}
    2017-05-21
    T12:13:14
    SHOP TY …
    11 Newsletter

    Subscription
    ‹UUID-HW› 2 Interval was
    changed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    12 Newsletter

    Subscription
    ‹UUID-HW› 3 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    13 Newsletter
    Subscription
    ‹UUID-HW› 4 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    14 Newsletter

    Subscription
    ‹UUID-HW› 5 Topic was assigned {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    15 Newsletter

    Subscription
    ‹UUID-HW› 6 Subscription was
    confirmed
    {"json"} 2017-05-22
    T10:09:08
    SHOP TY …
    33 Newsletter

    Subscription
    ‹UUID-HW› 7 Subscription was
    canceled
    {"json"} 2017-05-25
    T07:09:09
    SHOP DE …
    50 Newsletter

    Subscription
    ‹UUID-HW› 8 Subscription was
    reactivated
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    51 Newsletter

    Subscription
    ‹UUID-HW› 9 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    52 Newsletter
    Subscription
    ‹UUID-HW› 10 Topic was removed {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    53 Newsletter

    Subscription
    ‹UUID-HW› 11 Interval was
    changed
    {"json"} 2017-06-01
    T14:15:16
    SHOP DE …
    54 Newsletter

    Subscription
    ‹UUID-HW› 12 Subscription was
    confirmed
    {"json"} 2017-06-02
    T16:17:18
    SHOP DE …
    65
    EVENT STORE
    SECOND SUBSCRIPTION
    PLEASE NOTE:
    EXPRESS EXACTLY WHAT YOU ARE DOING
    INITIATED !== REACTIVATED
    AVOID AGGREGATION OF CHANGES
    YOU’LL LOSE VALUABLE INFORMATION
    Topics were changed !== Topic was added + Topic was removed
    

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66. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT STORE PAYLOAD
    66
    {
    "SubscriptionID": "‹UUID-HW›",
    "Fullname": "Holger Woltersdorf",
    "Email": "hollodotme@PHPkonf.org"
    }
    "Subscription was initialised"
    {
    "SubscriptionID": "‹UUID-HW›"
    }
    vs.
    "Subscription was reactivated"
    

    View Slide

67. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT STORE PAYLOAD
    67
    DO NOT ADD PREVIOUS VALUES TO PAYLOAD
    IT SHOULD HAVE BEEN RECORDED BEFORE
    STOP THINKING RELATIONAL
    START THINKING TEMPORAL
    

    View Slide

68. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING
    68
    interface EventInterface
    {
    public function getStreamID() : StreamIDInterface
    public function getEventID() : EventID
    public function getPayload() : Payload
    public static function fromPayload( Payload $payload ) : EventInterface
    }
    interface EventEnvelopeInterface
    {
    public function getHeader() : EventHeaderInterface
    public function getEvent() : EventInterface
    }
    

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69. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING
    69
    interface EventHeaderInterface
    {
    public function getStreamType() : StreamType
    public function getStreamID() : StreamIDInterface
    public function getStreamSeq() : StreamSequence
    public function getOccurred() : Timestamp
    public function getMetaX() : ShopName
    public function getMeta…() : …
    }
    

    View Slide

70. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING
    70
    ๏ EVENT STORE IS IMMUTABLE AND APPEND-ONLY
    ๏ EVENT STORE IS THE ONLY SOURCE OF TRUTH
    ๏ USE TECHNOLOGY INDEPENDENT PAYLOAD FORMAT (XML/JSON/ETC.)

    DO NOT USE OBJECT SERIALISATION!
    ๏ EVENTS ARE IMMUTABLE
    ๏ SEPARATE PAYLOAD FROM META DATA (EVENT ENVELOPE)
    ๏ VALUE OBJECTS ARE IMMUTABLE
    ๏ EVENT STREAM IS A SORTED LIST OF EVENTS
    ๏ BUSINESS ENTITIES CAN NOT BE INSTANTIATED WITHOUT EVENT STREAM
    

    View Slide

71. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING (BUSINESS ENTITY)
    71
    class NewsletterSubscription
    {
    private $streamType;
    private $streamSeq;
    private $changes;
    # ...
    private function __construct()
    {
    $this->streamType = new StreamType( 'Newsletter Subscription' );
    $this->streamSeq = new StreamSeq( 0 );
    $this->changes = new EventStream();
    }
    # ...
    }
    

    View Slide

72. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING (BUSINESS ENTITY)
    72
    class NewsletterSubscription
    {
    public static function initiate(
    Email $email,
    Fullname $fullname
    ) : NewsletterSubscription
    {
    $subscription = new self();
    $subscription->recordThat(
    new SubscriptionWasInitiated(
    SubscriptionID::generate(),
    $email,
    $fullname
    )
    );
    return $subscription;
    }
    # ...
    }
    ๏ DO NOT CREATE ENTITIES
    WITHOUT RECORDING AN
    EVENT
    

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73. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING (BUSINESS ENTITY)
    73
    class NewsletterSubscription
    {
    #...
    private function recordThat( EventInterface $event ) : void
    {
    $envelope = EnvelopeBuilder::build(
    $this->getStreamType(),
    $this->streamSeq->increment(),
    $event
    );
    $this->changes->append( $envelope );
    $this->apply( EventEnvelopeInterface $envelope );
    }
    #...
    }
    

    View Slide

74. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING (BUSINESS ENTITY)
    74
    class NewsletterSubscription
    {
    #...
    private function apply( EventEnvelopeInterface $envelope ) : void
    {
    $header = $envelope->getHeader();
    $event = $envelope->getEvent();
    $this->streamSeq = $header->getStreamSeq();
    $methodName = 'when' . $event->getEventID()->toUpperCamelCase();
    $this->$methodName( $event );
    # $this->whenSubscriptionWasInitiated( $event );
    }
    #...
    }
    

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75. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING (BUSINESS ENTITY)
    75
    class NewsletterSubscription
    {
    #...
    protected function whenSubscriptionWasInitiated(
    SubscriptionWasInitiated $event
    ) : void
    {
    $this->email = $event->getEmail();
    $this->fullname = $event->getFullname();
    # This is your "real" constructor
    # Init properties here
    }
    #...
    }
    

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76. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING (BUSINESS ENTITY)
    76
    class NewsletterSubscription
    {
    #...
    public static function reconstitute( EventStream $eventStream ) : self
    {
    $subscription = new self();
    foreach ( $eventStream as $envelope )
    {
    $subscription->apply( $envelope );
    }
    return $subscription;
    }
    #...
    }
    

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77. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING (BUSINESS ENTITY)
    77
    abstract class AbstractBusinessEntity
    {
    final protected function __construct()
    final protected function recordThat( EventInterface $event ): void
    private function apply( EventEnvelopeInterface $envelope ) : void
    final public static function reconstitute( EventStream $eventStream )
    }
    

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78. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING (BUSINESS ENTITY)
    78
    class NewsletterSubscription extends AbstractBusinessEntity
    {
    private $topics;
    public function assignTopic( Topic $topic ) : void
    protected function whenTopicWasAssigned( TopicWasAssigned $event ) : void
    }
    class NewsletterSubscription extends AbstractBusinessEntity
    {
    use NewsletterSubscriptionChanging;
    public function assignTopic( Topic $topic ) : void
    }
    USE A TRAIT TO EXPOSE PUBLIC API ONLY
    trait NewsletterSubscriptionChanging
    {
    private $topics;
    protected function whenTopicWasAssigned( TopicWasAssigned $event ) : void
    }
    

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79. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING
    79
    ๏ QUESTIONS WE CAN ASK NOW:
    ๏ WHAT WAS THE (UN-)SUBSCRIBE RATIO IN 2016?
    ๏ HOW MANY USERS REACTIVATED THEIR SUBSCRIPTION IN 2017?
    ๏ HOW MANY USERS REACTIVATED MORE THAN ONCE?
    ๏ WHICH TOPIC WAS REMOVED THE MOST?
    ๏ HOW MANY USERS CHANGED INTERVAL BEFORE SUBSCRIPTION WAS CANCELED?
    

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80. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    80
    EVENT SOURCING
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    EVENT STORE
    PUBLISH SUBSCRIBE
    REDIRECT (+ SESSION)
    VIEW LOGIC
    READ HISTORY OF CHANGES
    RECORD NEW CHANGES
    

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81. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    RECORD NEW CHANGES
    READ HISTORY OF CHANGES
    81
    EVENT SOURCING
    READ REQUESTS
    BUSINESS LOGIC
    REPRESENTATION
    WRITE REQUESTS
    EVENT STORE
    PUBLISH SUBSCRIBE
    REDIRECT (+ SESSION)
    VIEW LOGIC
    

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82. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    RECORD NEW CHANGES
    READ HISTORY OF CHANGES
    82
    EVENT SOURCING (PROJECTION)
    READ REQUESTS
    BUSINESS LOGIC
    PROJECTION
    WRITE REQUESTS
    EVENT STORE
    PUBLISH SUBSCRIBE
    REDIRECT (+ SESSION)
    VIEW LOGIC
    

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83. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    RECORD NEW CHANGES
    READ HISTORY OF CHANGES
    83
    EVENT SOURCING (PROJECTION)
    READ REQUESTS
    BUSINESS LOGIC
    WRITE REQUESTS
    REDIRECT (+ SESSION)
    VIEW LOGIC
    REPRESENTATION
    REPRESENTATION
    EVENT STORE
    PUBLISH SUBSCRIBE
    PROJECTION
    MESSAGE
    BROKER
    ASYNC
    EVENTUAL
    CONSISTENCY
    !
    

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84. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING (PROJECTING)
    84
    ๏ PUSH VIEWS
    ๏ Gets notified about a new change (event)
    ๏ Can directly project this information
    ๏ PULL VIEWS
    ๏ Gets a query and pulls up appropriate event streams to gather information
    ๏ Can respond or project the result
    ๏ MIXED VIEWS
    ๏ Gets notified and gathers missing information from event store
    ๏ Projects this information
    

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85. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING (PROJECTING)
    85
    PLEASE NOTE:
    PROJECTIONS SHOULD CONVERT STATE INFORMATION
    TO THE BEST DATA FORMAT FOR YOUR READ-USE-CASE
    THIS COULD ALSO BE ANOTHER EVENT STORE
    WITH A SUBSET OF STREAMS / EVENTS
    

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86. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    CQRS ADVANTAGES
    86
    ๏ WHAT CAN WE GAIN FROM APPLYING CQRS?
    ๏ Separate input / output handling
    ๏ Opportunity to optimise each side for its operational purpose
    ๏ Depends on your application domain
    ๏ e.g. eCommerce Shops usually have a read / write ratio of 95% / 5%

    so optimisation for reading is a good idea
    ๏ Clean code, reusable queries and commands, decoupling, simpler tests
    ๏ No unintended side effects
    ๏ Technology independence for each side
    ๏ Good prerequisite for individual horizontal scalability
    

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87. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    EVENT SOURCING ADVANTAGES
    87
    ๏ WHAT CAN WE GAIN FROM USING EVENT SOURCING?
    ๏ High scalability
    ๏ Simplification of storing application state ("one size fits all")
    ๏ Traceability of all changes ever made to application state
    ๏ Retroactive data analysis at any time
    ๏ Adapting new business requirements with ease
    ๏ Restoring state representation at any given point in time
    ๏ Replay after bug fixes to re-establish view consistency
    ๏ Easy backup & restore
    

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88. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    88
    QUESTIONS?
    

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89. THANK YOU!
    github.com/hollodotme
    @hollodotme / @F9T3ch
    fortuneglobe.com
    phpug-dresden.org
    @phpugdd
    HOLGER WOLTERSDORF
    speakerdeck.com/hollodotme
    Slides available at:
    

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90. TOTAL RECALL - THE APPLICATION THAT NEVER FORGETS • OCT 28, 2018 • PHPCE. • PRAGUE HOLGER WOLTERSDORF
    LINKS / REFERENCES
    90
    ๏ CQS:
    ๏ https://martinfowler.com/bliki/CommandQuerySeparation.html
    ๏ https://en.wikipedia.org/wiki/Command%E2%80%93query_separation
    ๏ Bertrand Meyer:
    ๏ https://de.wikipedia.org/wiki/Bertrand_Meyer
    ๏ https://bertrandmeyer.com
    ๏ Book "Object-Oriented Software Construction 2Ed" by Bertrand Meyer: http://amzn.to/2qdnc2i
    ๏ Greg Young’s CQRS documents: https://cqrs.files.wordpress.com/2010/11/cqrs_documents.pdf
    ๏ GET/HEAD methods: https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html
    ๏ Article about Event Sourcing by Martin Fowler: https://martinfowler.com/eaaDev/EventSourcing.html
    ๏ PHP FastCGI Client: https://github.com/hollodotme/fast-cgi-client
    

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