Rails 3 problem loading classes from lib in config/environments/development.rb - ruby-on-rails

I'm working on upgrading a Rails 2.3.11 app to 3.0.10. I'm getting a NameError in my development.rb file, when I try to run any of the rails scripts like rails console, or run my unit tests.
I'm calling a class that I have defined in lib, but it seems that the library hasn't been loaded when development.rb calls the class.
I'm doing something like:
config.cache_store = CustomMemcachedStore.new(Memcached.new(...))
I have a file lib/custom_memcached_store.rb that declares the class
class CustomMemcachedStore < ActiveSupport::Cache::Store
I'm getting the following error:
~/.rvm/gems/ruby-1.9.2-p290/gems/rake-0.8.7/lib/rake.rb:2503:in `const_missing': uninitialized constant CustomMemcachedStore (NameError)
from ~/app_name/config/environments/development.rb:20:in `block in <top (required)>'
In application.rb, I am already using
config.autoload_paths += Dir["#{Rails.root}/lib"]
Thanks for any help you can give me.

You will need to require the file explicitly, rather than relying on autoload.
This is because the loading of the environment config happens early on in the startup process before autoload paths are set up.
In some cases you can work with initializers to insert configuration code into a place that works, via something like:
initializer "my_setup", :before => "some_other_setup" do |app|
# ...
end
Unfortunately, this is not one of those cases, as the cache is set up here, while the autoload paths are not set up until here, immediately before the boostrap_hook.

Related

Accessing modules in Rails lib folder

There are probably hundreds of these questions on here but I haven't been able to get one to work yet. I'm using Rails 6 and I always have trouble writing custom modules.
I have a file for creating email tokens: lib/account_management/email_token.rb
module AccountManagement
module EmailToken
def create_email_token(user)
....
end
end
end
Then in my controller I have tried all kinds of things:
require 'account_management/email_token'
include AccountManagement::EmailToken
Calling it with: create_and_send_email_token(user)
At one point I added config.eager_load_paths << Rails.root.join('lib/account_management/') but I didn't think you still had to do that.
Whenever I try to call the controller action I get one of a few error messages:
*** NameError Exception: uninitialized constant Accounts::SessionsController::EmailToken
#this happens if I try to manually send through the rails console
(although inside of a byebug I can call require 'account_management/email_token' and it returns
true.
Most commonly I get:
NoMethodError (undefined method `create_email_token' for #<Accounts::SessionsController:0x00007ffe8dea21d8>
Did you mean? create_email):
# this is the name of the controller method and is unrleated.
The simplest way to solve this is by placing your files in app/lib/account_management/email_token.rb. Rails already autoloads any subdirectory of the app folder*.
/lib has not been on the autoload paths since Rails 3. If you want to add it to the autoload paths you need to add /lib not /lib/account_management to the autoload/eager loading paths. In Zeitwerk terms this adds a root where Zeitwerk will index and resolve constants from.
config.autoload_paths += config.root.join('lib')
config.eager_load_paths += config.root.join('lib')
Note that eager_load_paths is only used when eager loading is turned on. Its turned off by default in development to enable code reloading.
/lib is added to $LOAD_PATHso you can also manually require the file with:
require 'account_management/email_token'
See:
Autoloading and Reloading Constants (Zeitwerk Mode)
Rails #37835

Zeitwerk error on devise mailer in production environment

I have Rails 6, my preview class located in
mailer/previews/devise_mailer_preview.rb:
class DeviseMailerPreview < ActionMailer::Preview
...
end
And when I run application locally, everything is going fine, I can see my email previews on http://localhost:3000/rails/mailers/devise_mailer/confirmation_instructions address. But now Im trying to deploy application on server, and found that when I run bundle exec rails c production, I got the error:
/home/deploy/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/zeitwerk-2.3.0/lib/zeitwerk/loader/callbacks.rb:17:in
`on_file_autoloaded': expected file
/home/deploy/project/releases/20200627024908/app/mailer/previews/devise_mailer_preview.rb
to define constant Previews::DeviseMailerPreview, but didn't
(Zeitwerk::NameError)
After that I've checked locally RAILS_ENV=production rails c, and got same.
If I will rename DeviseMailerPreview class to Previews::DeviseMailerPreview, it will be broken and I cannot see emails on development, because Rails 6, accordingly to docs, expect exactly that name.
More of that, I've found in this article, that zeitwerk can be configured with autoload_paths param to avoid ruby's NameError. I found that I have it my config/application.rb:
config.load_defaults 6.0
Anyway I tried to add same row in my config/environments/production.rb file, but it didn't help.
What am I doing wrong and how can I fix it? Thanks in advance!
Add preview_path to the autoload_paths and zeitwerk will expect DeviseMailerPreview constant to be defined.
# development.rb
config.action_mailer.preview_path = Rails.root.join("app/mailers/previews")
# application.rb
config.autoload_paths << Rails.root.join("app/mailers/previews")
Your Mailer preview file is located in mailer/previews/devise_mailer_preview.rb, so I'm assuming it's full path is app/mailer/previews/devise_mailer_preview.rb
The docs says
In the above example, the preview class for UserMailer should be named UserMailerPreview and located in test/mailers/previews/user_mailer_preview.rb
So put your devise_mailer_preview.rb file to test/mailers/previews/devise_mailer_preview.rb
or in your config/application.rb add this line and restart:
config.action_mailer.preview_path = "#{Rails.root}/app/mailers/previews"
Actually the answer was in the docs itself.
In Rails 6, previews are added to the autoload paths only if options.show_previews is true, which is not by default in the production environment. See the source code here.
The reason for this is that previews are supposed to be an aid for development, and they are generally not something you want to be able to look at in production.
However, you can set that flag to true in production if you want.
There's another derivative: By storing the previews under app/mailers, Rails is going to eager load them because app/mailers is in the autoload paths. If app/mailers/previews is not in the autoload paths, eager loading will fail due to the namespace mismatch. Either you have them enabled in all environments, or else is better to have them in a separate location, like the default.

Heroku - Uninitialized constant for importing a module

I have a module
lib/Basicstats.rb (module Basicstats ...etc. end)
I am importing this into a model
class Vote < ActiveRecord::Base
include Basicstats
#additional class code etc.
end
I grep-d for the module and 'Basicstats' is only referenced in Basicstats.rb and app/model/vote.rb.
This works fine for my local development. But during my Heroku deployment I am getting this error and it can't seem to recognize the module? (I'm also curious how this is working in my local development without a require anywhere.)
2015-03-28T22:19:52.714077+00:00 app[web.1]: /app/app/models/vote.rb:16:in `<class:Vote>': uninitialized constant Basicstats (NameError)
It sounds like your module isn't being explicitly required or auto-loaded by Rails (this will/won't happen depending which version of Rails you're using and how config.autoload_paths is configured).
Your best bet is to add an initializer which explicitly requires your module:
# config/initializers/basicstats.rb
require Rails.root.join('lib/basicstats')

Rails unable to autoload constant from file despite being defined in that file

This is a tricky one to explain. I have a module in another module namespace like so:
# app/models/points/calculator.rb
module Points
module Calculator
def self.included(base)
base.send(:include, CommonMethods)
base.send(:include, "Points::Calculator::#{base}Methods".constantize)
end
end
end
So then in other classes all I need to do is:
class User
include Points::Calculator
end
I've specified this directory in application.rb to be autoloadable...(even though i think rails recurses through models...)
config.autoload_paths += Dir[ Rails.root.join('app', 'models', "points") ]
In development env, everything works fine. When running tests(and production env), I get the following error:
Unable to autoload constant Points::Calculator, expected /Users/pete/work/recognize/app/models/points/calculator.rb to define it (LoadError)
I actually followed the advice here to fix the problem: Stop Rails from unloading a module in development mode by explicitly requiring calculator.rb in application.rb.
However, why is this happening??
I stuck some debug output in ActiveSupport's dependencies.rb file and noticed that this file is being required twice. The first time its required I can see that the constant is indeed loaded.
But the 2nd time its required the constant has been unloaded as far as Rails can tell, but when the actual require is called, ruby returns false because ruby knows its already required it. Then Rails throws the "unable to autoload constant" error because the constant still isn't present and ruby didn't "re-require" the file.
Can anyone shed light on why this might be happening?
Rails augments the constant lookup mechanism of ruby.
Constant lookup in Ruby:
Similar to method missing, a Module#constant-missing is invoked when a reference to a constant fails to be resolved. When we refer to a constant in a given lexical scope, that constant is searched for in:
Each entry in Module.nesting
Each entry in Module.nesting.first.ancestors
Each entry in Object.ancestors if Module.nesting.first is nil or a module.
When we refer to a constant, Ruby first attempts to find it according to this built-in lookup rules.
When ruby fails to find... rails kicks in, and using its own lookup convention and its knowledge about which constants have already been loaded (by ruby), Rails overrides Module#const_missing to load missing constants without the need for explicit require calls by the programmer.
Its own lookup convention?
Contrasting Ruby’s autoload (which requires the location of each autoloaded constant to be specified in advance) rails following a convention that maps constants to file names.
Points::Calculator # =>points/calculator.rb
Now for the constant Points::Calculator, rails searches this file path (ie 'points/calculator.rb') within the autoload paths, defined by the autoload_paths configuration.
In this case, rails searched for file path points/calculator in its autoloaded paths, but fails to find file and hence this error/warning is shown.
This answer is an abstract from this Urbanautomation blog.
Edit:
I wrote a blog about Zeitwerk, the new code reloader in Rails. Check it out at -> https://blog.bigbinary.com/2019/10/08/rails-6-introduces-new-code-loader-called-zeitwerk.html
If someone is having this issue in rails 6 which has zeitwerk autoloader,
Change ruby constant lookup back to classic in your application.rb
# config/application.rb
#...
config.autoloader = :classic
#...
Read more details here Rails Official Guides
Calculator should be a class to be autoloaded correctly
module Points
class Calculator
...
end
end

Where do you put your Rack middleware files and requires?

I'm in the process of refactoring some logic built into a Rails application into middleware, and one annoyance I've run into is a seeming lack of convention for where to put them.
Currently I've settled on app/middleware but I could just as easily move it to vendor/middleware or maybe vendor/plugins/middleware...
The biggest problem is having to require the individual files at the top of config/environment.rb
require "app/middleware/system_message"
require "app/middleware/rack_backstage"
or else I get uninitialized constant errors on the config.middleware.use lines. That could get messy very quickly. I'd rather this was tucked away in an initializer somewhere.
Is there a conventional place to put this stuff?
The specific answer I'm looking for with this bounty is: where can I put the require lines so that they are not cluttering the environment.rb file but still get loaded before the config.middleware.use calls? Everything I have tried leads to uninitialized constant errors.
Update: Now that we're using Rails 3.0, I treat a Rails app like any other Rack app; code files for middleware go in lib (or a gem listed in Gemfile) and are required and loaded in config.ru.
As of Rails 3.2, Rack middleware belongs in the app/middleware directory.
It works "out-of-the-box" without any explicit require statements.
Quick example:
I'm using a middleware class called CanonicalHost which is implemented in app/middleware/canonical_host.rb. I've added the following line to production.rb (note that the middleware class is explicitly given, rather than as a quoted string, which works for any environment-specific config files):
config.middleware.use CanonicalHost, "example.com"
If you're adding middleware to application.rb, you'll need to include quotes, as per #mltsy's comment.
config.middleware.use "CanonicalHost", "example.com"
You can put it in lib/tableized/file_name.rb. As long as the class you're trying to load is discoverable by its filename, Rails will automatically load the file necessary. So, for example:
config.middleware.use "MyApp::TotallyAwesomeMiddleware"
You would keep in:
lib/my_app/totally_awesome_middleware.rb
Rails catches const_missing and attemts to load files corresponding to the missing constants automatically. Just make sure your names match and you're gravy. Rails even provides nifty helpers that'll help you identify the path for a file easily:
>> ChrisHeald::StdLib.to_s.tableize.singularize
=> "chris_heald/std_lib"
So my stdlib lives in lib/chris_heald/std_lib.rb, and is autoloaded when I reference it in code.
In my Rails 3.2 app, I was able to get my middleware TrafficCop loading by putting it at app/middleware/traffic_cop.rb, just as #MikeJarema described. I then added this line to my config/application.rb, as instructed:
config.middleware.use TrafficCop
However, upon application start, I kept getting this error:
uninitialized constant MyApp::Application::TrafficCop
Explicitly specifying the root namespace didn't help either:
config.middleware.use ::TrafficCop
# uninitialized constant TrafficCop
For some reason (which I've yet to discover), at this point in the Rails lifecycle, app/middleware wasn't included in the load paths. If I removed the config.middleware.use line, and ran the console, I could access the TrafficCop constant without any issue. But it couldn't find it in app/middleware at config time.
I fixed this by enclosing the middleware class name in quotes, like so:
config.middleware.use "TrafficCop"
This way, I would avoid the uninitialized constant error, since Rails isn't trying to find the TrafficCop class just yet. But, when it starts to build the middleware stack, it will constantize the string. By this time, app/middleware is in the load paths, and so the class will load correctly.
For Rails 3:
#config/application.rb
require 'lib/rack/my_adapter.rb'
module MyApp
class Application < Rails::Application
config.middleware.use Rack::MyAdapter
end
end
I'm not aware of a convention, but why not put it in the /lib directory? Files in there get automatically loaded by Rails.
You could create an initializer which requires the necessary files and then leave the files wherever you want.
According to this the initializers are executed before the rack middleware is loaded.
The working solution I have so far is moving the middleware requires to config/middleware.rb and requiring that file in environment.rb, reducing it to a single require which I can live with.
I'd still like to hear how other people have solved this seemingly basic problem of adding middleware to Rails.

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