A Copy of Xxx Has Been Removed from the Module Tree But Is Still Active

A copy of xxx has been removed from the module tree but is still active

Tenant is sort of a red herring - the error would occur if you referenced any bit of app that needs to be loaded by rails' const_missing trick.

The problem is that you are taking something reloadable (your module) and then including it in something not reloadable (ActiveRecord::Base or, in your earlier example ActionMailer::Base). At some point your code is reloaded and now ActiveRecord still has this module included in it even though rails thinks it has unloaded it. The error occurs when you reference Tenant because that causes rails to run its const_missing hooks to find out where Tenant should be loaded from and that code freaks out because the module where the constant search is starting from shouldn't be there.

There are 3 possible solutions:

1. Stop including your module into non reloadable classes - either include into individual models, controllers as needed or create an abstract base class and include the module in there.

2. Make this module non reloadable by storing it somewhere that isn't in autoload_paths (you'll have to require it explicitly since rails will no longer load it magically for you)

3. Changing Tenant to ::Tenant (Object.const_missing will then be invoked, not Tenant.const_missing)

ArgumentError (A copy of Api::V1 has been removed from the module tree but is still active!)

As the stack trace suggests, this is a dependancy clash of the app with ActiveSupport. I recommend using the gem bootsnap. Bootsnap overrides ActiveSupport::Dependencies which is causing the issue in the first place. It also improves the app's load time which is actually what it is designed for. From Bootsnap documentation:

ActiveSupport::Dependencies.{autoloadable_module?,load_missing_constant,depend_on} are overridden to eliminate scans of ActiveSupport::Dependencies.autoload_paths.

A copy of XXX has been removed from the module but is still active

I don't think that provided error is somehow related to the code above.
Usually, this error happens when you modify your classes at runtime with metaprogramming.

Take a look at places where you require, define ExamResult, it looks like you require it several times in your code.

A copy of ApplicationController has been removed from the module tree but is still active

This is a bug in Rails 2.3.3:

• https://rails.lighthouseapp.com/projects/8994/tickets/2948-exception-a-copy-of-actorscontroller-has-been-removed-from-the-module-tree-but-is-still-active

There is a patch for it (but incomplete?) in 2-3-stable:

• http://github.com/rails/rails/commit/d37ac7958fc88fdbf37a8948102f6b4e45c530b3

You have a few options to address the problem:

• Revert to Rails 2.3.2, wait for 2.3.4 to come out, probably at the end of August. 2.3.3 has a couple bad issues, so that might be best.
• The problem should not happen in production mode, nor will it happen in development mode under the Thin server. If you are having this issue on Google Engines in production mode, the patch is your only hope. If it's only in dev mode, you can just run your local server with Thin instead of Mongrel.
• If it is Google Engines, you can move off of Google Engines and host your app another way. This seems like a lot of work though.

Best of luck, this is a really bad bug many people are running into.

ArgumentError: A copy of ApplicationController has been removed from the module tree but is still active

I'm not sure exactly why this is happening, but I found a workaound. Change this:

def current_permission
  @current_permission ||= Permissions.permission_for(current_user)
end

To this:

def current_permission
  @current_permission ||= ::Permissions.permission_for(current_user)
end

The error is raised at this point in ActiveSupport:

# Load the constant named +const_name+ which is missing from +from_mod+. If
# it is not possible to load the constant into from_mod, try its parent
# module using +const_missing+.
def load_missing_constant(from_mod, const_name)
  log_call from_mod, const_name

  unless qualified_const_defined?(from_mod.name) && Inflector.constantize(from_mod.name).equal?(from_mod)
    raise ArgumentError, "A copy of #{from_mod} has been removed from the module tree but is still active!"
  end
  # ...
end

The problem only occurs when you don't fully qualify the constant name, so Rails tries looking it up in the ApplicationController namespace.

Rails reloading classes and 'has been removed from the module tree but is still active!' ArgumentError

The first approach looks cleaner -

Adding path where may 'FooBar::ControllerRuntimeis defined
toconfig.autoload_one_paths`

Reasons -

1) If you really wanna do some monkey patches in file like lib/extensions.rb, you may manually require it:

in config/initializers/require.rb:

require "#{Rails.root}/lib/extensions"

2) Follows proper naming conventions as you will have to list down the class and module .

I wouldn't suggest auto-loading for production application though , but if it's the last option than you can certainly try it out .

Good read here on the same - http://www.williambharding.com/blog/technology/rails-3-autoload-modules-and-classes-in-production/

Rails: A copy of MetricBase has been removed from the module tree but is still active

I'm still not sure what the original issue is/was. A workaround was to use zeus and kill and restart the server after an edit.

A better solution I am now using is putting the classes in a module Metrics and it works.

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