Gem "audited-activerecord", "~> 4.0 gives undefined method `audits' - ruby-on-rails

Question

I am using:
Rail 4.1.7
Ruby 2.1.4
I just installed Audited GEM:
gem "audited-activerecord", "~> 4.0"
$ rails generate audited:upgrade
$ rake db:migrate
Model
class Opportunity < ActiveRecord::Base
...
audited
...
end
And when I run:
Opportunity.audits.count
I get this error:
2.1.4 :001 > Opportunity.audits.count
NoMethodError: undefined method `audits' for #<Class:0x007ff7946656f0>
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/activerecord-4.1.7/lib/active_record/dynamic_matchers.rb:26:in `method_missing'
from (irb):1
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/railties-4.1.7/lib/rails/commands/console.rb:90:in `start'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/railties-4.1.7/lib/rails/commands/console.rb:9:in `start'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/railties-4.1.7/lib/rails/commands/commands_tasks.rb:69:in `console'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/railties-4.1.7/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/railties-4.1.7/lib/rails/commands.rb:17:in `<top (required)>'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/activesupport-4.1.7/lib/active_support/dependencies.rb:247:in `require'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/activesupport-4.1.7/lib/active_support/dependencies.rb:247:in `block in require'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/activesupport-4.1.7/lib/active_support/dependencies.rb:232:in `load_dependency'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/activesupport-4.1.7/lib/active_support/dependencies.rb:247:in `require'
from /Users/andreucasadella/rails_projects/crm/bin/rails:8:in `<top (required)>'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/activesupport-4.1.7/lib/active_support/dependencies.rb:241:in `load'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/activesupport-4.1.7/lib/active_support/dependencies.rb:241:in `block in load'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/activesupport-4.1.7/lib/active_support/dependencies.rb:232:in `load_dependency'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/activesupport-4.1.7/lib/active_support/dependencies.rb:241:in `load'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/spring-1.2.0/lib/spring/commands/rails.rb:6:in `call'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/spring-1.2.0/lib/spring/command_wrapper.rb:38:in `call'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/spring-1.2.0/lib/spring/application.rb:183:in `block in serve'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/spring-1.2.0/lib/spring/application.rb:156:in `fork'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/spring-1.2.0/lib/spring/application.rb:156:in `serve'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/spring-1.2.0/lib/spring/application.rb:131:in `block in run'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/spring-1.2.0/lib/spring/application.rb:125:in `loop'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/spring-1.2.0/lib/spring/application.rb:125:in `run'
from /Users/andreucasadella/.rvm/gems/ruby-2.1.4/gems/spring-1.2.0/lib/spring/application/boot.rb:18:in `<top (required)>'
from /Users/andreucasadella/.rvm/rubies/ruby-2.1.4/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /Users/andreucasadella/.rvm/rubies/ruby-2.1.4/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from -e:1:in `<main>'2.1.4
I am using Ruby 2.1.4 and there is a warning sign "Audited may work just fine with a Ruby version not listed above (Latested 2.1.2), but we can't guarantee that it will. If you'd like to maintain a Ruby that isn't listed, please let us know with a pull request."
Has anyone experienced this before?

Answer 1

The audits method is an instance method, i.e. it is for one opportunity, not the entire Opportunity class.
Your code:
Opportunity.audits.count # Fails because audits is not a class method.
Solution code:
opportunity = Opportunity.first # any search you want
opportunity.audits.count # Succeeds because audits is an instance method.