Rails 3 Autoload Modules/Classes – 3 Easy Fixes

Judging by the number of queries on Stack Overflow, it is a very common problem for folks using Rails 3 that they are not getting the modules or classes from their lib directory loaded in Rails 3, especially in production. This leads to errors like “NoMethodError,” “No such file to load [file in your lib path],” and “uninitialized constant [thing you're trying to load].” From the information I canvassed trying to solve the problem this morning, there are three common reasons (and one uncommon reason) that this can happen. I’ll go in order of descending frequency.

1. You haven’t included the lib directory in your autoload path

Rails 3 has been updated such that classes/modules (henceforth, C/M) are lazy loaded from the autoload paths as they are needed. A common problem, especially for the newly upgraded, is that the C/M you are trying to load isn’t in your autoload path. Easy enough fix:

config.autoload_paths += Dir["#{config.root}/lib/**/"]

This will autoload your lib directory and any subdirectories of it. Similarly, if you have model subdirectories, you may need to add

config.autoload_paths += Dir["#{config.root}/app/models/**/"]

To your application.rb file.

2. Your C/M is not named in the way Rails expects

Rails has opinions about what the name of your C/M should be, and if you name it differently, your C/M won’t be found. Specifically, the namespace for your C/M should match the directory structure that leads to it. So if you have a C/M with the filename “search.rb” in the lib/google directory, it’s name should be “Google::Search.” The name of the C/M should match the filename, and the name of the directory (in this case “Google”) should be part of the namespace for your module. See also this.

3. Your application is threadsafe.

This was one that was hard to find on SO or Google, but if you have configured your application to be threadsafe (done by default in production.rb), then the C/Ms you have, even if they exist in your autoload path, will not be defined until you require them in your application. According to the Rails docs, there is apparently something not threadsafe about automatically loading the C/Ms from their corresponding files. To workaround this, you can either require your individual library files before you use them, or comment out config.threadsafe!

4. (Esoteric) You have a model in a subdirectory, where the name of the subdirectory matches the name of the model.

Yes, this is another error we actually had when upgrading from Rails 2 to 3: as of Rails 3.0.4 there is a bug wherein, if you have a directory app/models/item and you have the file “item.rb” in your app/models/item directory, then you will get errors from Rails that your models are undefined (usually it picks the second model in the item subdirectory). We fixed this by just renaming our subdirectories where appropriate. Hopefully in one of the next versions of Rails this will get fixed and no longer be a possible problem.

Had other reasons why C/Ms failed to load for you? Do post below and we can gather up all the possibilities in one tidy location.

14 thoughts on “Rails 3 Autoload Modules/Classes – 3 Easy Fixes

  1. #1 didn’t work for me.

    Instead, I made a new file config/initializers/requires.rb:

    # Require modules in lib
    Dir[File.join(Rails.root, 'lib', '*.rb')].each do |f|
    require f
    end

  2. Thank you. Point 3 is maddening and possibly the most poorly documented aspect of rails I have run into.

  3. Ok figured it out.

    The AWS/SW gem overwrites Module#const_missing — and messes with things if you class ends in ‘Bucket’. Man, that was a great use of 6 hrs. No idea why it only happens when coupled with InheritedResources, but that clearly is the root of the problem.

  4. I have a fifth reason ;-)
    I declared a module inside lib/JLA/common_person.rb

    module JLA
    module CommonPerson
    # definition here
    end
    end

    and added lib to the autoload_paths in config/application.rb

    The dumbest point here is that on Heroku I had to rename the directory JLA/ in jla/ .. :o )

  5. Building on Rahil’s solution:

    YourApp::Application.config.paths['lib'].each do |lib_path|
    Dir[File.join(Rails.root, lib_path, '**', '*.rb')].each { |f| require f}
    end

    So as not to hardcode the lib path…there also may be more that one.

  6. It could be I’m SOL here, but I just encountered this with an upgrade from Rails 2 to Rails 3.

    I have app/models/order.rb which defines the Order class as expected.

    In my lib directory, i have a C/M of lib/some_api_integration/order.rb which defines SomeApiIntegration::Order.

    However, now my app expects lib/some_api_integration/order.rb to define my Order model, which isn’t good for a functional app.

    I’m prepared to just rename my API integration class or Order model to something other than order.rb, but would rather not, as it makes the most sense as it’s used for interacting with e-commerce orders, and the Order model keeps tabs on some additional attributes of retrieved orders.

  7. Well €¦as it turns out, with some experimentation I learned that changing my config.autoload_paths from Dir["#{config.root}/lib/**/"] to explicitly calling each lib directory I want to autoload, and then implementing an initializer for my API that utilizes the example Paul & Rahil sported, I was able to work around the conflicting class names.

    Interesting.

  8. What worked for me, besides following those fixes above, was to create a initializer like this:
    #config/initializers/myapp_init.rb
    require ‘mymodule’
    include ‘mymodule’

    #if I include inside my AR class, it DOESN’T work!
    I’m on Rails 3.1.3

  9. Beware the trap of just renaming the class file with lowercase, committing and pushing to heroku. I just spent hours trying to solve this problem, when the only problem was that either git or heroku didn’t actually change the name of the file on the heroku server to the lowercase version.

    Once I deleted the file, committed that change, and then re-added with lowercase letters, it worked.

  10. The most frustrating part of this issue is that it all works well in development mode but it blows up in production mode which is not a preferred place for debugging. I am doing deployment of my first ruby app on heroku and I lost almost a a day chasing this issue of loading things from lib directory. I hope that rails resolves in future release to avoid production time headaches.

  11. @Will DelHagen – Great shout! I did exactly the same thing about 2 hours ago and have been hacking away ever since.

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