This document presents Aecor, a framework for purely functional event sourcing, detailing its toolkit, modular architecture, and relational behaviors. It includes a comprehensive overview of event handling through operations like debiting accounts, managing events, and processing in a distributed environment. Additionally, it highlights advantages such as scalability, composability, and applications in asynchronous processing and event-based service integration.

1. Aecor
Purely functional event sourcing
Denis Mikhaylov
@notxcain
Aecor ⇒ Purely functional event sourcing by @notxcain 1

2. Vanilla
id owner balance
1 John 50
do debitAccount(accountId: AccountId, amount: Amount) = for {
state <- loadState(accountId)
(nextState, result) <- state.debit(amount)
_ <- saveState(accountId, nextState)
} yield result
Aecor ⇒ Purely functional event sourcing by @notxcain 2

3. Event sourcing
id seqNr event
Account-1 1 Opened(John)
Account-1 2 Credited(100)
Account-1 3 Debited(50)
Aecor ⇒ Purely functional event sourcing by @notxcain 3

4. Event sourcing
do debitAccount(accountId: AccountId, amount: Amount) = for {
events <- loadEvents(accountId)
state = events.foldLeft(zeroState)(_ applyEvent _)
(newEvents, result) <- state.debit(amount)
_ <- appendEvents(accountId, newEvents)
} yield result
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5. Event
• What?
• When?
• Who?
• Where?
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6. Isn’t that great?
• Change log
• Complex temporal, retroactive queries
• Time-travel debugging
• Scalable, HA stores (Cassandra, Couchbase, etc.)
• Event based service integration (reactive bla bla)
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7. Toolkit?
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8. Toolkit?
• Purely functional behaviors
• Purely functional runtime
• Scalable
• Composable
• Testable
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9. Aecorhttps://aecor.io
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10. Aecor
• modular framework library
• composable primitives
• runtimes
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11. Akka Persistence Runtime
• akka-cluster-sharding
• akka-persistence
• akka-persistence-cassandra
• cats
• typesafe encoding/decoding
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12. Behavior
final case class EventsourcedBehavior[F[_], Op[_], State, Event](
handler: Op ~> Handler[F, State, Event, ?],
zero: State,
reducer: (State, Event) => Folded[State]
)
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13. State
zero: S
reducer: (S, E) => Folded[E]
sealed abstract class Folded[+A] extends Product with Serializable
final case object Impossible extends Folded[Nothing]
final case class Next[+A](a: A) extends Folded[A]
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14. Operations
trait RepliesWith[A]
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15. Operations
trait RepliesWith[A]
sealed abstract class AccountOp[A] extends Product with Serializable {
def accountId: AccountId
}
final case class OpenAccount(accountId: AccountId)
extends AccountOp[Either[OpenAccountRejection, Unit]]
final case class CreditAccount(accountId: AccountId, transactionId: AccountTransactionId, amount: Amount)
extends AccountOp[Either[CreditAccountRejection, Unit]]
final case class DebitAccount(accountId: AccountId, transactionId: AccountTransactionId, amount: Amount)
extends AccountOp[Either[DebitAccountRejection, Unit]]
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16. Operation handler
type Handler[F[_], S, E, A] =
S => F[(Seq[E], A)]
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17. Operation handler
type Handler[F[_], S, E, A] =
S => F[(Seq[E], A)]
type VanillaHandler[F[_], S, A] =
S => F[(S, A)]
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18. Operation handler
type Handler[F[_], S, E, A] =
S => F[(Seq[E], A)]
type OperationHandler[F[_], Op[_], S, E] =
Op ~> Handler[F, S, E, ?]
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19. Behavior
final case class EventsourcedBehavior[F[_], Op[_], State, Event](
handler: Op ~> Handler[F, State, Event, ?],
zero: State,
reducer: (State, Event) => Folded[State]
)
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20. Show Time
class AkkaPersistenceRuntime[F[_]: Async: CaptureFuture: Capture: Monad](system: ActorSystem) {
def start[Op[_], State, Event: PersistentEncoder: PersistentDecoder](
entityName: String,
correlation: Correlation[Op], // Op[_] => String
behavior: EventsourcedBehavior[F, Op, State, Event],
tagging: Tagging[Event], // Event => EventTag[Event]
snapshotPolicy: SnapshotPolicy[State],
settings: AkkaPersistenceRuntimeSettings
): F[Op ~> F] = ...
}
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21. Event tagging
AccountOpened(1, John) -> Account0
AccountOpened(2, Mike) -> Account1
AccountOpened(3, Bill) -> Account0
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22. Reading events
trait EventJournalQuery[Offset, E] {
def eventsByTag(
tag: EventTag[E],
offset: Option[Offset]
): Source[JournalEntry[Offset, E], NotUsed]
}
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23. Reading events
trait EventJournalQuery[Offset, E] {
def committableEventsByTag[F[_]: Async](
offsetStore: OffsetStore[F, Offset],
tag: EventTag[E],
consumerId: ConsumerId
): Source[Committable[F, JournalEntry[Offset, E]], NotUsed]
}
final case class Committable[F[_], +A](commit: F[Unit], value: A)
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24. Process
1. React to changes (events, time)
2. Perform actions
3. ???
4. PROFIT Eventual Consistency
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25. Co-things?
Entity : Actions -> Changes
Process : Changes -> Actions
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26. Process
Top 2
• Views
• Business-processes
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27. Distributed Processing
final case class Process[F[_]](run: F[RunningProcess[F]])
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28. Distributed Processing
final case class Process[F[_]](run: F[RunningProcess[F]])
final case class RunningProcess[F[_]](
watchTermination: F[Unit],
shutdown: () => Unit
)
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29. Distributed Processing
def start[F[_]: Async: Capture: CaptureFuture: Functor](
name: String,
processes: Seq[Process[F]],
settings: DistributedProcessingSettings
): F[ProcessKillSwitch[F]] = ...
final case class ProcessKillSwitch[F[_]](shutdown: F[Unit])
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30. Aecor - what else?
Experimental runtime for generic behaviors
final case class Behavior[F[_], Op[_]](run: Op ~> PairT[F, Behavior[F, Op], ?])
class GenericAkkaRuntime[F[_]: Async: CaptureFuture: Functor: Capture](system: ActorSystem) {
def start[Op[_]](entityName: String,
correlation: Correlation[Op],
behavior: Behavior[F, Op],
settings: GenericAkkaRuntimeSettings
): F[Op ~> F]
}
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31. Aecor - what else?
Liberator (free algebra for trait, and many more)
@algebra
trait Account[F[_]] {
def openAccount(accountId: AccountId, owner: AccountOwner): F[Either[OpenAccountRejection, Unit]]
}
class EventSourcedAccount[F[_]](clock: F[ZonedDateTime])
extends Account[Handler[F, AccountState, AccountEvent, ?]]
val account: EventSourcedAggregate[Task] = ...
val handler: AccountOp ~> Handler[F, AccountState, AccountEvent, ?] = account.asFunctionK
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32. Adopters
• Evotor (https://evotor.ru)
• Your name here
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33. Q&Ahttps://aecor.io
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