@fraktalio/fmodel-ts
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Functional domain modeling with TypeScript. Optimized for event sourcing and CQRS
141 lines • 11.8 kB
JavaScript
/*
* Copyright 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.
*/
/**
* An abstract algorithm to compute new events based on the old events and the command being handled.
*/
export class EventComputation {
constructor(decider) {
this.decider = decider;
this.initialState = decider.initialState;
}
decide(command, state) {
return this.decider.decide(command, state);
}
evolve(state, event) {
return this.decider.evolve(state, event);
}
computeNewEvents(events, command) {
const currentState = events.reduce(this.decider.evolve, this.decider.initialState);
return this.decider.decide(command, currentState);
}
}
/**
* An abstract algorithm to compute new events based on the old events and the command being handled.
* It returns all the events, including the events created by handling commands which are triggered by Saga - orchestration included.
*/
export class EventOrchestratingComputation {
constructor(decider, saga) {
this.decider = decider;
this.saga = saga;
this.initialState = decider.initialState;
}
decide(command, state) {
return this.decider.decide(command, state);
}
evolve(state, event) {
return this.decider.evolve(state, event);
}
react(event) {
return this.saga.react(event);
}
computeNewEventsInternally(events, command) {
const currentState = events.reduce(this.decider.evolve, this.decider.initialState);
return this.decider.decide(command, currentState);
}
async computeNewEvents(events, command, fetch) {
// eslint-disable-next-line functional/no-let
let resultingEvents = this.computeNewEventsInternally(events, command);
await asyncForEach(resultingEvents.flatMap((evt) => this.saga.react(evt)), async (cmd) => {
const newEvents = this.computeNewEvents((await fetch(cmd)).map((evt) => evt).concat(resultingEvents), cmd, fetch);
resultingEvents = resultingEvents.concat(await newEvents);
});
return resultingEvents;
}
}
/**
* Event sourcing aggregate is using/delegating a `EventSourcingAggregate.decider` of type `IDecider`<`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 `IEventRepository.fetchEvents` function, and then delegate the command to the `EventSourcingAggregate.decider` which can produce new event(s) as a result.
*
*
* Produced events are then stored via `IEventRepository.save` function.
*
* @typeParam C - Commands of type `C` that this aggregate can handle
* @typeParam S - Aggregate state of type `S`
* @typeParam E - Events of type `E` that this aggregate can publish
* @typeParam E - Version
* @typeParam CM - Command Metadata
* @typeParam EM - Event Metadata
*
* @author Иван Дугалић / Ivan Dugalic / @idugalic
*/
export class EventSourcingAggregate extends EventComputation {
constructor(decider, eventRepository) {
super(decider);
this.eventRepository = eventRepository;
}
async fetch(command) {
return this.eventRepository.fetch(command);
}
async versionProvider(event) {
return this.eventRepository.versionProvider(event);
}
async save(events, commandMetadata, versionProvider) {
return this.eventRepository.save(events, commandMetadata, versionProvider);
}
async handle(command) {
const currentEvents = await this.eventRepository.fetch(command);
return this.eventRepository.save(this.computeNewEvents(currentEvents, command), command, async () => currentEvents[currentEvents.length - 1]);
}
}
/**
* Event sourcing orchestrating aggregate is using/delegating a `EventSourcingOrchestratingAggregate.decider` of type `IDecider`<`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 `IEventRepository.fetchEvents` function, and then delegate the command to the `EventSourcingOrchestratingAggregate.decider` which can produce new event(s) as a result.
*
* If the `EventSourcingOrchestratingAggregate.decider` is combined out of many deciders via `combine` function, an optional `EventSourcingOrchestratingAggregate.saga` could be used to react on new events and send new commands to the `EventSourcingOrchestratingAggregate.decider` recursively, in one transaction.
*
* Produced events are then stored via `IEventRepository.save` function.
*
* @typeParam C - Commands of type `C` that this aggregate can handle
* @typeParam S - Aggregate state of type `S`
* @typeParam E - Events of type `E` that this aggregate can publish
* @typeParam V - Version
* @typeParam CM - Command Metadata
* @typeParam EM - Event Metadata
*
* @author Иван Дугалић / Ivan Dugalic / @idugalic
*/
export class EventSourcingOrchestratingAggregate extends EventOrchestratingComputation {
constructor(decider, eventRepository, saga) {
super(decider, saga);
this.eventRepository = eventRepository;
}
async fetch(command) {
return this.eventRepository.fetch(command);
}
async versionProvider(event) {
return this.eventRepository.versionProvider(event);
}
async save(events, commandMetadata, versionProvider) {
return this.eventRepository.save(events, commandMetadata, versionProvider);
}
async handle(command) {
const currentEvents = await this.eventRepository.fetch(command);
return this.eventRepository.save(await this.computeNewEvents(currentEvents, command, async (cmd) => await this.eventRepository.fetch(cmd)), command, this.versionProvider.bind(this));
}
}
async function asyncForEach(array, callback) {
for (let index = 0; index < array.length; index++) {
await callback(array[index], index, array);
}
}
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VyRCxLQUFLLElBQUksS0FBSyxHQUFHLENBQUMsRUFBRSxLQUFLLEdBQUcsS0FBSyxDQUFDLE1BQU0sRUFBRSxLQUFLLEVBQUUsRUFBRSxDQUFDO1FBQ2xELE1BQU0sUUFBUSxDQUFDLEtBQUssQ0FBQyxLQUFLLENBQUMsRUFBRSxLQUFLLEVBQUUsS0FBSyxDQUFDLENBQUM7SUFDN0MsQ0FBQztBQUNILENBQUMifQ==