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CQRS & Event Sourcing in OLX
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Łukasz Szymański
May 16, 2016
Programming
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1.9k
CQRS & Event Sourcing in OLX
Łukasz Szymański
May 16, 2016
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Transcript
CQRS Event Sourcing in OLX
CQRS
you can use a different model to update information than
the model you use to read information http://martinfowler.com/bliki/CQRS.html „
Command Query Responsibility Segregation
Command Query Responsibility Segregation
new AddCredits($userId, $amount); Command
Command new AddCredits($userId, $amount); Query new GetCredits($userId);
Event Sourcing
http://www.martinfowler.com/eaaDev/EventSourcing.html „ ensures that all changes to application state are
stored as a sequence of events
Not just can we query these events, we can also
use the event log to reconstruct past states http://www.martinfowler.com/eaaDev/EventSourcing.html „
Commad Event Model Event Storage Event Bus Command Handler Listeners
Read Storage Read Model Query
Commad Event Model Event Storage Event Bus Command Handler Listeners
Read Storage Read Model Query Critical section - use transaction
Commad Event Model Event Storage Event Bus Command Handler Listeners
Read Storage Read Model Query Critical section - use transaction Treat like temporary cache
That’s all
E-Wallet Credits; Invoices; Refunds
Wallet Credits Bonus Credits Refund Credits EXPIRE: X DAYS EXPIRE:
X DAYS EXPIRE: X DAYS INVOICE: YES/NO INVOICE: YES/NO INVOICE: YES/NO
Wallet Credits Bonus Credits Refund Credits EXPIRE: NEVER EXPIRE: 90
DAYS EXPIRE: 90 DAYS INVOICE: YES INVOICE: NO INVOICE: YES
Opis walleta w Polsce specyfikacja komenty enventy Commands
Add Wallet Credits Add Bonus Credits Add Refund Credits
Sub Wallet Credits Sub Bonus Credits Sub Refund Credits SubCredits
Opis walleta w Polsce specyfikacja komenty enventy Events
Wallet CreditsWasAdded Bonus CreditsWasAdded Refund CreditsWasAdded
Wallet CreditsWasSubtracted Bonus CreditsWasSubtracted Refund CreditsWasSubtracted
specyfikacja komenty enventy 7 commands 6 events
specyfikacja komenty enventy What about other stuff?
Commad Event Model Event Storage Event Bus Command Handler Listeners
Read Storage Read Model Query ?
Broadway komponenty Broadway https://github.com/qandidate-labs/broadway
Auditing log whether commands were successful or not
CommandHandling Provides the interface and a CommandHandler base class for
handling events
Domain domain abstractions of the Broadway framework including the aggregate
root, domain messages and domain events.
EventDispatcher The component provides an event dispatcher interface and a
simple implementation
EventHandling provides interfaces for an event bus and event listeners,
but also an implementation of a simple event bus and an event bus that will record published events
EventSourcing Provides base classes for event sourced aggregate roots and
entities, an event sourced repository implementation and testing helpers.
EventStore implementation based on doctrine/dbal to store events in a
relational database and an in-memory implementation that is useful for using in tests
ReadModel provides storage for your read models, a projector implementation
to create read models from event streams and testing helpers.
Repository Component providing an abstraction of the storage of aggregates.
Serializers provides a simple serializer interface and a serializer implementation
based on "handwritten" serializers
Commad Event Model Event Storage Event Bus Command Handler Listeners
Read Storage Read Model Query Broadway
Adding Wallet Credits
None
None
Credits Query
None
None
Lessons Learned
Small Steps Don’t try to CQRS/EventSource everything
Keep It Simple Avoid names like BonusCreditsWasSubtractedBecauseAdminHitSubtractBonusCr editsInAdminPanelEvent
Event Storming is not that easy as it sounds
It’s not RDBM Remember about analysts
Code changes Events handle changes to data, what about changes
to code?
Synchronize Remember about synchronizing read layer - especially after fail
Commad Event Model Event Storage Event Bus Command Handler Listeners
Read Storage Read Model Query Critical section - use transaction
Performance is not an issue - for this case
Timezone Agnostic Implement your own EventStore if you want timezone
aware records
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Łukasz Szymański Development Team Lead at @szymanskilukasz http://szymanskilukasz.github.io/ https://www.linkedin.com/in/szymanskilukasz https://twitter.com/szymanskilukasz