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Trying EventStoreDb connector

Note on nodeJS version

You'll find a compatible version you refer to in this .nvmrc. You might want to use nvm direcly, and in this case, nvm will read direcly this configuration file and adjust the version.

Installation

yarn install

Start

You have to run a eventstore container with correct ports. You can put the ports you want, but it will work natively with this conf :

docker run --name esdb-node -d \
    -it -p 2113:2113 -p 1113:1113 \
    eventstore/eventstore:latest \
    --insecure \
    --run-projections=All \
    --enable-atom-pub-over-http

Then, the REST API will start by running :

yarn start

Usage

running basic CQRS example with eventStore

The example is based on CQRS module usage example of Nest framework.

Story

The hero fight the dragon in an epic fight. he kills the dragon, and a dragon can be killed only once. We need to keep only the last 5 move of the fight and delete them after 3 days for faery RGPD.

When it's done the hero search and find an item.
He can find this special item only once until he drop hit.

How to connect

You can see how the import is done in the EventStoreHeroesModule :

    CqrsEventStoreModule.register(
      eventStoreConnectionConfig,
      eventStoreSubsystems,
      eventBusConfig,
    ),

Let's run it

Once the API is running, you only have to run this REST request :

curl -XPUT localhost:3000/hero/200/kill -d'{ "dragonId" : "test3" }'

All the events emitted by the example will be stored in the event store.

You can call it multiple time to try idemptotency see events on the dashboard of event store

What the code does

  • heroes.controller send to the command bus kill-dragon.command configured with http body
  • kill-dragon.handler fetch the hero and build a hero.aggregate merging db and command data
  • kill-dragon.handler call killEnemy() on hero.aggregate
  • hero.aggregate kill the enemy and apply hero-killed-dragon.event
  • kill-dragon.handler commit() on hero.aggregate (write all events on aggregate)
  • Eventstore stores the event on event's stream, applying idempotency (mean if you do it twice event is ignored the other times)
  • hero-killed-dragon.handler receive the event from Eventstore and log (can run in another process)
  • heroes-sagas receive the event from Eventstore do some logic and send to commandBus drop-ancient-item-command
  • drop-ancient-item.handler fetch the hero and build a hero.aggregate merging db and command data
  • drop-ancient-item.handler addItem() on hero.aggregate
  • hero.aggregate apply hero-found-item.event
  • drop-ancient-item.handler dropItem() on hero.aggregate
  • hero.aggregate apply hero-drop-item.event
  • kill-dragon.handler commit() on hero.aggregate (can be done after each call)
  • Eventstore store the event on event's stream

Data transfer object

Stupid data object with optionnals validation rules

Repository

Link with the database (mocked here)

Aggregate Root

Where everything on an entity and it's child appends.
Updated only using events

Command

Data transfer object with a name that you must execute

Command handler

Do the logic : Read the Command, merge DB and command's data on the Aggregate, play with aggregate's methods, commit one or multiple time when needed

Event

Data transfer object with a name and a stream name.
Can have a UUID, metadata and an expected version

Event Handler

Do the side effects. Receive event and do logic with them : usually update or insert on the database

Saga

Side effects that create new commands. Receive events and return one or more commands.