CQRS and Event Sourcing

CQRS and Event Sourcing are becoming buzzwords nowadays. This presentation tries to clarify both concepts and present a simple example application, written with those powerful architectures

Transcript

1. CQRS
   EVENT SOURCING
   

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5. Christian Soronellas
   Web Enthusiast
   @theUniC
   theUniC
   

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8. Exploration of concepts (CQRS and ES)
   Practical use case
   Conclusions
   

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9. #phpbcn
   https://github.com/theUniC/blog-cqrs
   

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10. ¿What is CQRS?
    

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11. It’s an architectural pattern
    

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12. Asking a question
    should not change the answer
    

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13. Methods that return state information should
    not trigger side effects
    

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14. !
    namespace An\Awesome\Namespace;
    !
    class AnAmazingService
    {
    /** @var An\Awesome\Dependency */
    private $aDependency;
    !
    public function getDependency()
    {
    if (null === $this->aDependency) {
    $this->aDependency = new \An\Awesome\Dependency();
    }
    !
    return $this->aDependency;
    }
    !
    public function anIncredibleAction()
    {
    $aDependency = $this->getDependency();
    $aDependency->performSomethingNeeded();
    // ...
    }
    }
    

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15. !
    namespace An\Awesome\Namespace;
    !
    class AnAmazingService
    {
    /** @var An\Awesome\Dependency */
    private $aDependency;
    !
    public function getDependency()
    {
    if (null === $this->aDependency) {
    $this->aDependency = new \An\Awesome\Dependency();
    }
    !
    return $this->aDependency;
    }
    !
    public function anIncredibleAction()
    {
    $aDependency = $this->aDependency;
    $aDependency->performSomethingNeeded();
    // ...
    }
    }
    

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16. CQRS challenges the assumption that
    reading and writing are supposed
    to share the same abstractions
    

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17. !
    namespace AcmeShop\Billing\DomainModel\Order;
    !
    interface OrderRepository
    {
    /** return Order */
    public function get(OrderId $anId);
    }
    

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18. !
    namespace AcmeShop\Billing\DomainModel\Order;
    !
    interface OrderRepository
    {
    /** @return Order */
    public function get(OrderId $anId);
    !
    /** @return Order[] */
    public function getByUser(UserId $aUserId);
    }
    

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19. !
    namespace AcmeShop\Billing\DomainModel\Order;
    !
    interface OrderRepository
    {
    /** @return Order */
    public function get(OrderId $anId);
    !
    /** @return Order[] */
    public function byUser(UserId $aUserId);
    !
    /** @return OrderWithAge[] */
    public function allGroupedByAge();
    }
    

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20. !
    namespace AcmeShop\Billing\DomainModel\Order;
    !
    interface OrderRepository
    {
    /** @return Order */
    public function get(OrderId $anId);
    !
    /** @return Order[] */
    public function byUser(UserId $aUserId);
    !
    /** @return OrderWithAge[] */
    public function allGroupedByAge();
    !
    /** @return OrderWithCarrier[] */
    public function allGroupedByCarrier();
    }
    

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21. Command
    sends
    Command Handler
    is handled by
    Write
    Model
    uses
    Event Subscriber
    triggers
    writes
    reads from
    Read
    Model
    queries
    User Interface
    synchronizes with
    returns
    

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22. Command
    sends
    Command Handler
    is handled by
    Write
    Model
    uses
    Event Subscriber
    triggers
    writes
    reads from
    Read
    Model
    queries
    Eventual Consistency™
    User Interface
    synchronizes with
    returns
    

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23. Write
    Model
    Event
    Event
    Event
    Event
    

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24. Events are fundamental part in DDD
    

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25. We can express the system state as a sequence !
    of events that have occurred
    

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27. POST
    COMMENT
    has many
    belongs to
    AUTHOR
    is written by an
    writes many
    

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28. [
    {
    "type":"PostWasCreated",
    "created_at": "2014-06-11 18:00:00",
    "data":"{'post_id': 1, 'title': '...', 'content': '...'}"
    }
    ]
    

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29. [
    {
    "type":"PostWasCreated",
    "created_at": "2014-06-11 18:00:15",
    "data": "{'post_id': 1, 'title': '...', 'content': '...'}"
    },
    {
    "type": "PostWasPublished",
    "created_at": "2014-06-11 18:05:35",
    "data": "{'post_id': 1}"
    }
    ]
    

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30. [
    {
    "type":"PostWasCreated",
    "created_at": "2014-06-11 18:00:15",
    "data": "{'post_id': 1, 'title': '...', 'content': '...'}"
    },
    {
    "type": "PostWasPublished",
    "created_at": "2014-06-11 18:05:35",
    "data": "{'post_id': 1}"
    },
    {
    "type": "CommentWasCreated",
    "created_at": "2014-06-11 18:15:20",
    "data": "{'post_id': 1, 'comment_id': 1, 'comment': '...'}"
    }
    ]
    

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31. Event
    Event
    Event
    Event Store™
    

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32. PostWasCreated
    CommentWasAdded
    PostWasPublished
    Event Store™
    

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33. Event Sourcing
    

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34. Practical use case
    

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35. Conclusions
    

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36. CQRS and ES combined provide a simple solution
    for complex problems
    

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37. CQRS allow reads and writes to scale independently
    

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38. Event Sourcing allow to perform a more efficient and more
    exhaustive debugging
    

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39. Event Sourcing grants not to be tightly coupled with any
    structure nor any implementation
    

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40. They’re not the silver bullet
    Use it wisely
    

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41. ¡Thanks!
    

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