EventLogging

Plugin for event logging in rails application.

Read our article (sorry French only)

Installation

Add this line to your application's Gemfile :

gem'event_logging',git: 'git@github.com:Snapp-FidMe/event-logging.git',branch: :master

Import migrations with :

 bundle exec event_logging:install:migrations

Require Rails 5. or later and Postgresql with jsonb (9.6 or greater).

Tests

Configure database in test/dummy/config/database.yml then play migrations :

 RAILS_ENV=test bundle exec rake db:migrate

And launch tests :

 bundle exec rake test

Event

Events carry this data :

• stream_id => Write model ID
• aggregate_name => Model name
• action => operation which raised event (create, update, destroy or custom)
• created_at
• payload => hash that contains model changes

Write models

Write models are business logic models. Use the Writer concern :

classReward < ApplicationRecordincludeEventLogging::Writer# Business stuffend

Then after each create or update an event will be inserted in database, and associated read models will have to manage the event.

All the process is in callback transaction so data will be consistent over exceptions.

Write model can dispatch custom events :

reward.dispatch_event_log!('custom_action','the'=>'payload')

Read models

Read models are data projection. Use the Reader concern :

classRewardLog < ApplicationRecordincludeEventLogging::Readerregister_write_models:reward,:retailerclass << selfdefhandle_event_log(event)ifevent.aggregate_name == Reward.namehandle_reward_event_log(event)elsifevent.aggregate_name == Retailer.namehandle_retailer_event_log(event)endenddefhandle_reward_event_log(event)ifevent.action == 'create'RewardLog.create!(reward_id: event.stream_id,status: event.payload['status'][1],retailer_id: event.payload['retailer_id'][1]retailer_name: Retailer.find(event.payload['retailer_id'][1]).name)elsifevent.action == 'update' && event.payload.has_key?['status']reward=Reward.find(event.stream_id)RewardLog.create!(reward_id: event.stream_id,status: event.payload['status'][1],retailer_id: reward.retailer.idretailer_name: reward.retailer.name)endenddefhandle_retailer_event_log(event)ifevent.payload.has_key?('name')Reward.where(retailer_id: event.stream_id).find_eachdo |reward|
reward.update_attributes!(retailer_name: event.payload['name'][1])endendendendend

Default payload is saved_changes from Rails.

Be careful : synchronised read models slow write operations in order to speed up read operations.