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#202 Introducing snapshotting event sourced aggregate - draft 2
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.../commonMain/kotlin/com/fraktalio/fmodel/application/EventSourcingSnapshottingAggregate.kt
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| /* | ||
| * Copyright (c) 2023 Fraktalio D.O.O. All rights reserved. | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
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| package com.fraktalio.fmodel.application | ||
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| import com.fraktalio.fmodel.domain.IDecider | ||
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| /** | ||
| * Event sourced, snapshotting aggregate is using/delegating a `decider` of type [IDecider]<[C], [S], [E]>/ [EventComputation]<[C], [S], [E]> to handle commands and produce events. | ||
| * In order to handle the command, aggregate needs to fetch the current state (represented as a list of events) via [EventSnapshottingRepository.fetchEvents] function, and then delegate the command to the `decider` which can produce new event(s) as a result. | ||
| * Produced events are then stored via [EventSnapshottingRepository.save] suspending function. | ||
| * | ||
| * Additionally, Event sourcing aggregate enables `snapshotting` mechanism by using [StateComputation] and [StateRepository] interfaces to store and fetch the current state of the aggregate from time to time, removing the need to always fetch the full list of events. | ||
| * | ||
| * [EventSourcingSnapshottingAggregate] extends [EventComputation], [StateComputation], [StateRepository] and [EventSnapshottingRepository] interfaces, | ||
| * clearly communicating that it is composed out of these behaviours. | ||
| * | ||
| * @param C Commands of type [C] that this aggregate can handle | ||
| * @param S Aggregate state of type [S] | ||
| * @param E Events of type [E] that this aggregate can publish | ||
| * | ||
| * @author Иван Дугалић / Ivan Dugalic / @idugalic | ||
| */ | ||
| interface EventSourcingSnapshottingAggregate<C, S, E> : | ||
| EventComputation<C, S, E>, | ||
| StateComputation<C, S, E>, | ||
| EventSnapshottingRepository<C, S, E>, | ||
| StateRepository<C, S> | ||
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| /** | ||
| * Event sourced, snapshotting, locking aggregate is using/delegating a `decider` of type [IDecider]<[C], [S], [E]>/ [EventComputation]<[C], [S], [E]> to handle commands and produce events. | ||
| * In order to handle the command, aggregate needs to fetch the current state (represented as a list of events) via [EventSnapshottingLockingRepository.fetchEvents] function, and then delegate the command to the `decider` which can produce new event(s) as a result. | ||
| * Produced events are then stored via [EventSnapshottingLockingRepository.save] suspending function. | ||
| * | ||
| * Additionally, Event sourcing aggregate enables `snapshotting` mechanism by using [StateComputation] and [StateRepository] interfaces to store and fetch the current state of the aggregate from time to time, removing the need to always fetch the full list of events. | ||
| * | ||
| * Locking Event sourcing aggregate enables `optimistic locking` mechanism more explicitly. | ||
| * If you fetch events from a storage, the application records the `version` number of that event stream. | ||
| * You can append new events, but only if the `version` number in the storage has not changed. | ||
| * If there is a `version` mismatch, it means that someone else has added the event(s) before you did. | ||
| * | ||
| * [EventSourcingSnapshottingLockingAggregate] extends [EventComputation], [StateComputation], [StateLockingRepository] and [EventSnapshottingLockingRepository] interfaces, | ||
| * clearly communicating that it is composed out of these behaviours. | ||
| * | ||
| * @param C Commands of type [C] that this aggregate can handle | ||
| * @param S Aggregate state of type [S] | ||
| * @param E Events of type [E] that this aggregate can publish | ||
| * @param V Version | ||
| * | ||
| * @author Иван Дугалић / Ivan Dugalic / @idugalic | ||
| */ | ||
| interface EventSourcingSnapshottingLockingAggregate<C, S, E, V> : | ||
| EventComputation<C, S, E>, | ||
| StateComputation<C, S, E>, | ||
| EventSnapshottingLockingRepository<C, S, E, V>, | ||
| StateLockingRepository<C, S, V> | ||
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| /** | ||
| * Event Sourced Snapshotting aggregate constructor-like function. | ||
| * | ||
| * The Delegation pattern has proven to be a good alternative to implementation inheritance, and Kotlin supports it natively requiring zero boilerplate code. | ||
| * | ||
| * @param C Commands of type [C] that this aggregate can handle | ||
| * @param S Aggregate state of type [S] | ||
| * @param E Events of type [E] that are used internally to build/fold new state | ||
| * @param decider A decider component of type [IDecider]<[C], [S], [E]> | ||
| * @param eventRepository An aggregate event repository of type [EventSnapshottingRepository]<[C], [S], [E]> | ||
| * @return An object/instance of type [EventSourcingSnapshottingAggregate]<[C], [S], [E]> | ||
| * | ||
| * @author Иван Дугалић / Ivan Dugalic / @idugalic | ||
| */ | ||
| fun <C, S, E> EventSourcingSnapshottingAggregate( | ||
| decider: IDecider<C, S, E>, | ||
| eventRepository: EventSnapshottingRepository<C, S, E>, | ||
| stateRepository: StateRepository<C, S> | ||
| ): EventSourcingAggregate<C, S, E> = | ||
| object : EventSourcingAggregate<C, S, E>, | ||
| EventSnapshottingRepository<C, S, E> by eventRepository, | ||
| StateRepository<C, S> by stateRepository, | ||
| IDecider<C, S, E> by decider {} | ||
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| /** | ||
| * Event Sourced Snapshotting and Locking aggregate constructor-like function. | ||
| * | ||
| * The Delegation pattern has proven to be a good alternative to implementation inheritance, and Kotlin supports it natively requiring zero boilerplate code. | ||
| * | ||
| * @param C Commands of type [C] that this aggregate can handle | ||
| * @param S Aggregate state of type [S] | ||
| * @param E Events of type [E] that are used internally to build/fold new state | ||
| * @param V Version | ||
| * @param decider A decider component of type [IDecider]<[C], [S], [E]> | ||
| * @param eventRepository An aggregate event repository of type [EventSnapshottingLockingRepository]<[C], [S], [E], [V]> | ||
| * @return An object/instance of type [EventSourcingSnapshottingLockingAggregate]<[C], [S], [E], [V]> | ||
| * | ||
| * @author Иван Дугалић / Ivan Dugalic / @idugalic | ||
| */ | ||
| fun <C, S, E, V> EventSourcingSnapshottingLockingAggregate( | ||
| decider: IDecider<C, S, E>, | ||
| eventRepository: EventSnapshottingLockingRepository<C, S, E, V>, | ||
| stateRepository: StateLockingRepository<C, S, V> | ||
| ): EventSourcingSnapshottingLockingAggregate<C, S, E, V> = | ||
| object : EventSourcingSnapshottingLockingAggregate<C, S, E, V>, | ||
| EventSnapshottingLockingRepository<C, S, E, V> by eventRepository, | ||
| StateLockingRepository<C, S, V> by stateRepository, | ||
| IDecider<C, S, E> by decider {} |