An Entity–Component–System reimagining of ActiveRecord that stays idiomatic to Ruby on Rails.

v0.1 — working, not yet published to RubyGems. The full v0.1 API is implemented and tested (468 examples), with a companion bulletin-board app built entirely on it. Publishing is a deliberate later step. See the v0.1 retrospective.

Replace one-table-per-model with one-table-per-component. An entity is a lightweight identity row. All state and behaviour live in small, reusable components composed onto it.

class User < ApplicationEntity
  component Name
  component Email
  component Avatar
end

class Email < ApplicationComponent
  validates :address, presence: true

  def send_welcome_email
    # self is the Email, never the User
  end
end

user = User.create!            # one row in `entities`, no component rows
user.email                     # => #<Email> — virtual, not persisted
user.email.address = "a@b.com"
user.save!                     # now `emails` gets a row

user.send_welcome_email        # delegated to the Email component
Email.where(verified: false)   # components are queried directly

Components are lazy: if every attribute equals its default, no row exists. They are shared by type, so Likes behaves identically on a Post and a Comment — no STI for state, no polymorphic associations, no inheritance.

Systems are plain Ruby objects that process components without ever loading an entity:

Email.pending.find_each(&:send_welcome_email)

The demo is built alongside the gem, not after it. If a feature feels awkward in the demo, that's the signal the API is wrong. See PROCESS.md.

ecs_rails everywhere except the Gemfile — see ADR-0007.

gem "ecs_on_rails"   # Gemfile — the packaging name
require "ecs_rails"  # everything else

Only the published gem name differs. RubyGems collapses -, _ and case when comparing names, so ecs-rails, ecs_rails and ecsrails are one name — and it belongs to an unrelated, still-maintained gem. ecs_on_rails keeps the rails keyword without the rails- prefix that convention reserves for Rails Core Team gems.

docs/architecture.md — the invariants. Everything else refers back to it.

Then the ADRs for why the design is the way it is, and the RFCs for what's built and what's next.

Worth knowing up front, because the honest version is more useful than the pitch:

• ADR-0002 — entity identity still uses a discriminator column. What ECS Rails eliminates is STI for state and behaviour, not for identity.
• ADR-0003 — a component can't require its own presence. That's the entity's business.
• ADR-0005 — one component instance per entity, always. The biggest constraint the design imposes.

Requires Ruby >= 3.2 and PostgreSQL.

cd gem
createdb ecs_rails_test
bundle install
bundle exec rspec

MIT. See LICENSE.