model-patterns

Model Patterns (37signals)

Rich domain models over service objects. Business logic lives in models, not in separate service classes.

Project knowledge

Tech Stack: Rails 8.2 (edge), UUIDs everywhere, database-backed everything (no Redis) Patterns: Heavy use of concerns, default values via lambdas, Current for context

Commands:

bin/rails generate model Card title:string body:text board:references:uuid
bin/rails generate migration AddColorToCards color:string
bin/rails db:migrate
bin/rails test test/models/
bin/rails console

Rich model vs service object

# BAD -- service object
class CloseCardService
  def initialize(card, user)
    @card = card
    @user = user
  end

  def call
    ActiveRecord::Base.transaction do
      @card.create_closure!(user: @user)
      @card.track_event("card_closed", user: @user)
    end
  end
end

# GOOD -- rich model
class Card < ApplicationRecord
  include Closeable

  def close(user: Current.user)
    create_closure!(user: user)
    track_event "card_closed", user: user
    notify_recipients_later
  end
end

# Controller simply calls:
@card.close

Model structure

Order within a model:

class Card < ApplicationRecord
  # 1. Concern includes
  include Assignable, Closeable, Eventable, Searchable, Watchable

  # 2. Associations
  belongs_to :account, default: -> { board.account }
  belongs_to :board, touch: true
  belongs_to :column, touch: true
  belongs_to :creator, class_name: "User", default: -> { Current.user }

  has_many :comments, dependent: :destroy
  has_many :assignments, dependent: :destroy
  has_one :closure, dependent: :destroy

  # 3. Validations
  validates :title, presence: true
  validates :status, inclusion: { in: %w[draft published archived] }

  # 4. Enums
  enum :status, { draft: "draft", published: "published", archived: "archived" }, default: :draft

  # 5. Scopes
  scope :recent, -> { order(created_at: :desc) }
  scope :positioned, -> { order(:position) }
  scope :active, -> { open.published.where.missing(:not_now) }

  # 6. Delegations
  delegate :name, to: :board, prefix: true, allow_nil: true

  # 7. Callbacks (sparingly)
  after_create_commit :broadcast_creation

  # 8. Business logic methods
  def publish
    update!(status: :published)
    track_event "card_published"
  end

  def move_to_column(new_column)
    update!(column: new_column)
    track_event "card_moved", particulars: {
      from_column_id: column_id_before_last_save,
      to_column_id: new_column.id
    }
  end

  private

  def broadcast_creation
    broadcast_prepend_to board, :cards, target: "cards", partial: "cards/card"
  end
end