EventSourcery::Postgres

A PostgreSQL event store and projections adapter for EventSourcery.

EventSourcery::Postgres is in production use at Envato.

• Ruby >= 2.6.0
• PostgreSQL

The event store relies on the uuid-ossp PostgreSQL extension (enabled automatically by EventSourcery::Postgres::Schema.create_events) and the Sequel pg_json extension (loaded automatically when you assign a database connection in the configuration).

Add this line to your application's Gemfile:

gem 'event_sourcery-postgres'

EventSourcery::Postgres.configure do |config|
  config.event_store_database = Sequel.connect(...)
  config.projections_database = Sequel.connect(...)
  config.write_events_function_name = 'writeEvents'
  config.events_table_name = :events
  config.aggregates_table_name = :aggregates
  config.callback_interval_if_no_new_events = 60
end

Before events can be stored or projected the required tables and database functions need to be created. Once the databases are configured (see above), create the event store schema:

# Creates the events table, the aggregates table, and the `writeEvents`
# database function on the event store database.
EventSourcery::Postgres::Schema.create_event_store

Projectors and reactors track their progress in a tracker table. By default this table is created automatically the first time a processor runs (via the auto_create_projector_tracker config option). To create it explicitly instead:

EventSourcery::Postgres::Schema.create_projector_tracker

Each of these methods accepts keyword arguments (db:, events_table_name:, etc.) if you need to override the defaults taken from the configuration.

ItemAdded = EventSourcery::Event

EventSourcery::Postgres.config.event_store.sink(ItemAdded.new(aggregate_id: uuid, body: {}))
EventSourcery::Postgres.config.event_store.get_next_from(0).each do |event|
  puts event.inspect
end

class ItemProjector
  include EventSourcery::Postgres::Projector

  table :items do
    column :item_uuid, 'UUID NOT NULL'
    column :title, 'VARCHAR(255) NOT NULL'
  end

  project ItemAdded do |event|
    table(:items).insert(item_uuid: event.aggregate_id,
                         title: event.body.fetch('title'))
  end
end

class UserEmailer
  include EventSourcery::Postgres::Reactor

  emits_events SignUpEmailSent

  process UserSignedUp do |event|
    emit_event SignUpEmailSent.new(user_id: event.aggregate_id) do
      UserMailer.signed_up(...).deliver
    end
  end
end

EventSourcery::EventProcessing::ESPRunner.new(
  event_processors: [item_projector, user_emailer],
  event_store:      EventSourcery::Postgres.config.event_store,
  stop_on_failure:  true,
).start!

After checking out the repo, run bin/setup to install dependencies. (This will install dependencies and recreate the test database.) Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install.

To release a new version:

1. Update the version number in lib/event_sourcery/postgres/version.rb
2. Get this change onto main via the normal PR process
3. Run bundle exec rake release, this will create a git tag for the version, push tags up to GitHub, and upload the gem to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/envato/event_sourcery-postgres.

The gem is available as open source under the terms of the MIT License.