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Reload Required Files in Rails

When a Rails project grows, I often notice the need to refactor domain logic into a separate module, isolated from Rails framework.

The isolated module will still stay in the main Rails app codebase, but can be easily packaged as a Ruby gem, tested separately, and used in other related applications.

Requirements

During the refactoring, we want to:

  1. Use require to load the module like a normal gem. If possible, no dependency on Rails autoload features such asrequire_dependency and autoload_paths.

  2. Edit the module without restarting server during development. In other words, we need to find a way to reload the module on every request.

Reload require files

After some research, I found a working solution by Timothy Cardenas:

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ActionDispatch::Callbacks.to_prepare do
  if Object.const_defined?("Module1")
    Object.send(:remove_const, "Module1")
  end
  $".delete_if {|s| s.include?('module1') }
  require 'module1'
end

What it does is, before each request,

  1. Unload the top-level module.
  2. Un-require all required files from the module.
  3. Re-require the top-level module.

An extra step in Rails 3.2

In Rails 3.2, ActionDispatch::Callbacks.to_prepare has a slightly different behavior. It will run before a request only if a watchable file is modified.

You need to specify your own watchable files:

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# watch all .rb files recursively under modules/module1/ dir
config.watchable_dirs['modules/module1'] = [:rb]

Introduce require_reloader gem

Before bundling the solution into a gem, I did a search on RubyGems.org and found Colin Young’s gem_reloader. It’s based on Timy’s solution as well. I forked it and started playing around.

In the end, I made some major changes to include Rails 3.2 support, some fixes and new features.

So I decided to release it as a new Ruby gem: require_reloader.

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# config/environments/development.rb
YourApp::Application.configure do
  ...
  RequireReloader.watch :module1,
    path: 'modules/module1'
end

Currently it supports Rails 3, including 3.1 and 3.2.

If you are working on something similar, looking forward for your feedbacks and pull requests. It is not tested on Rails 2 yet, so pull requests are definitely welcomed!

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