phuocph / rails-autoloading

Rails constants and autoloading

Autoload

In a rails application

1. We have model PointTransaction inside module Ps

  module Ps
    class PointTransaction
      ...
    end
  end

2. We have an api controller Api::V1::Ps::DailyLoginsController

class Api::V1::Ps::DailyLoginsController
  # I1
  def index
    @txs = Ps::PointTransaction.all
  end

  # I2
  def index
    @txs = ::Ps::PointTransaction.all
  end
end

• I1

  • Parent namepsace as the algorithm here, we have

    • Api::V1::Ps::DailyLoginsController
    • Api::V1::Ps
    • Api::V1
    • Api
    • top namespace

  • Resolve Ps::PointTransaction processes by this procedure follows the above parent namespaces in order:

    • First run Api::V1::Ps::DailyLoginsController
      Cannot found api/v1/ps/daily_logins_controller/ps.rb
      Cannot found api/v1/ps/daily_logins_controller/ps
Ps is existed on the parent Api::V1::Ps => raise NameError`
      Following the logic

      If none of the parent namespaces of the class or module has the missing constant then Rails assumes the reference is relative. Otherwise qualified.

      That above logics force Ps must be defined on direct parent namespace Api::V1::Ps::DailyLoginsController => Finally the NameError is: uninitialized constant Api::V1::Ps::DailyLoginsController::Ps

  • Solution

    • Use top namespace ::Ps::PointTransaction
    • Make Ps load first out side the moduel. E.gs puts Ps
    • Use require_dependency
    • Change module controller different from model or otherwise
      • Api::V1::Ps::DailyLoginsController to Api::V1::Cs::DailyLoginsController
        OR
      • Ps::PointTransaction to Cs::PointTransaction

• I2

  • ::Ps::PointTransaction.all will force Ps was found on top namesapce => It'll run fine

Relative References vs Qualified References

1. Load Top namespace User before

  puts User

  module Admin
    class UsersController
      puts Admin::User
    end
  end

Bonus Api::V1::Ps::DailyLoginsController was defined (also as the procedure)

1. Find Api

2. Find Api::V1

3. Find Api::V1::Ps

4. Find Api::V1::Ps::DailyLoginsController

5. Normal load

  module Admin
  class UsersController
      puts Admin::User
    end
  end

• 1 will get error because when puts Admin::User execute, User's already existed. User here is a quanlified references => force find user in admin/user.rb as describe here
• 2 will run as normal because when puts Admin::User run, User constant is still not existed, Rails will consider User as relative refernece => load top namespace User.
• Note: This above is only true when these code run only (run first)