Slick eventsourcing
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Slides for Scaladays 2016 presentation, "Transactional Event Sourcing using Slick"
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Slick eventsourcing
- 1. TRANSACTIONAL EVENT SOURCING USING SLICK ADAM WARSKI
- 3. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI EVENT SOURCING? ▸ All changes in the system are captured as a sequence of events
- 4. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI WHY EVENT SOURCING? ▸ IT: Information Technology ▸ do not loose information! ▸ Audit log ▸ Re-create system state
- 5. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI ME + AUDIT = HIBERNATE ENVERS
- 6. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI ME ▸ coder @ ▸ Lightbend consulting partner ▸ mainly Scala ▸ open-source: MacWire, ElasticMQ, Bootzooka, … ▸ http://www.warski.org / @adamwarski
- 7. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI THE GOAL ▸ Get the benefits of Event Sourcing … ▸ … still being able to leverage RDBMS features ▸ transactions ▸ schema ▸ SQL
- 8. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI OTHER APPROACHES ▸ Event Store (https://geteventstore.com) ▸ Akka Persistence (http://doc.akka.io/docs/akka/current) ▸ Eventuate (http://eventuate.io) ▸ + more
- 9. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI EVENTS ▸ Immutable ▸ Primary source of truth ▸ Past tense
- 10. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI EVENTS ▸ Payload: arbitrary json (case class) ▸ Event type (name of class) ▸ Aggregate type & id ▸ Id, timestamp ▸ Transaction id ▸ User id
- 11. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI HOW? ▸ Events are stored in a dedicated table ▸ Basing on events, a read model is updated ▸ similar to what a “traditional” CRUD model could be ▸ Consistency: both done in a single transaction
- 12. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI SLICK ▸ We operate on DBIOAction[T] ▸ a description of actions to be done ▸ execution deferred later ▸ can be sequenced using flatMap ▸ yes, it’s a Monad
- 13. User data Transaction READ MODEL MODEL UPDATE EVENT LISTENER External systems EVENT PROCESSOR REGISTRYREGISTRYREGISTRY Events COMMAND
- 15. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI POTENTIAL PROBLEMS ▸ Ordering of concurrent events operating on the same aggregate root ▸ DBIOAction “leaks” ▸ Future wrapping
- 16. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI SUMMING UP: FUNCTIONS INVOLVED ▸ Commands: Data => CommandResult[S, F] that is, DBIOAction[(Either[S, F], List[Event])] ▸ Event listeners: Event => DBIOAction[List[Event]] ▸ Model updates: Event => DBIOAction[Unit]
- 17. ADAM WARSKI, SOFTWAREMILL @ADAMWARSKI LINKS ▸ https://github.com/softwaremill/slick-eventsourcing ▸ README+blog longer than code ▸ only a skeleton ▸ probably for customisation ▸ https://github.com/adamw/slick-eventsourcing-pres
- 18. THANK YOU!