CQRS and Event Sourcing for dummies – Objectives – CQS

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CQRS and Event Sourcing for dummies – Objectives – CQS

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cqrs-and-event-sourcing-for-dummies

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CQRS and Event Sourcing for dummies

Created by Felipe Fernández / @felipefzdz

About Me

Felipe Fernández

About the talk

  • 1. Objectives
  • 2. CQS
  • 3. CQRS
  • 4. Event Sourcing
  • 5. Related Concepts
  • 6. Conclusion

Objectives

  • Single Responsability Principle
  • Scalability
  • Model complex domains

CQS

  • Command-query separation. Created by Bertrand Meyer
  • Rethinking CRUD/REST
  • Rethinking Mock/Stub
  • Achieving better SRP at method level

CQRS

  • Levels of split
  • No split : PostsRepository
  • Split at class level : PostsReader and PostsPersister
  • Split at datastore level : Writes in RDBMS and Reads in NoSQL
  • Split at deployable level : Write, read and materializer services.

EVENT SOURCING

  • Append instead of update/delete in the write side
  • Command vs Event
  • CreatePost vs PostCreated

EVENT SOURCING BENEFITS

  • Easy to create new views from scratch
  • Audit
  • Debugabble
  • Disaster Recovery
  • Unified log, same original datastore for OLAP and OLTP

RELATED CONCEPTS

  • Aggregates
  • Microservices
  • Devops
  • Event Storming

Aggregates

  • Transactional Boundary
  • Materialised from event store or write side store
  • Command handler checks invariants of aggregates
  • Example: Total value of unpaid orders for a customer must not exceed that customer's credit limit
  • Customer credit and orders should be part of the same aggregate
  • Application or datastore locks. Race conditions

Microservices

  • Write, read and materialiser deployables
  • Different scalability needs
  • HTTP, Message queues... Different intercommunication protocols
  • Lose type safety accross services

Devops

  • Infra/ops gets more complicated
  • Spinning up a local environment is harder
  • Smoke tests are harder too
  • Devs and ops need to collaborate more in this context

Conclusion

  • Most sofisticated solution has a steep learning curve
  • It scales really well
  • Bring ubiquituous language to your system seamlessly
  • Super fun, but harder

Thank you

Any questions?

CQRS and Event Sourcing for dummies Created by Felipe Fernández / @felipefzdz