Rails Controller Conventions

A controller action's job: read params, call one service/query, respond. No business logic lives here.

Thin Actions — Delegate Everything

# Wrong — business logic inline
def create
  @group = UserGroup.find_by(invitation_token: params[:token])
  if @group && @group.users.count < @group.max_size
    user = @group.users.create(nickname: params[:nickname], login_code: SecureRandom.hex(4))
    redirect_to user
  else
    render :new, alert: "Group is full or token invalid"
  end
end