Don't load AR middleware at all unless AR::Base is defined, #1666

Changes.md

@@ -1,6 +1,7 @@
 HEAD
 -----------
 
+- Only activate the ActiveRecord middleware if ActiveRecord::Base is defined on boot. [#1666]
 - Add ability to disable jobs going to the DJQ with the `dead` option.
 ```ruby
 sidekiq_options :dead => false, :retry => 5

lib/sidekiq/middleware/server/active_record.rb

@@ -5,7 +5,7 @@ module Sidekiq
         def call(*args)
           yield
         ensure
-          ::ActiveRecord::Base.clear_active_connections! if defined?(::ActiveRecord)
+          ::ActiveRecord::Base.clear_active_connections!
         end
       end
     end

lib/sidekiq/processor.rb

@@ -1,7 +1,6 @@
 require 'sidekiq/util'
 require 'sidekiq/actor'
 
-require 'sidekiq/middleware/server/active_record'
 require 'sidekiq/middleware/server/retry_jobs'
 require 'sidekiq/middleware/server/logging'
 
@@ -22,7 +21,10 @@ module Sidekiq
       Middleware::Chain.new do |m|
         m.add Middleware::Server::Logging
         m.add Middleware::Server::RetryJobs
-        m.add Middleware::Server::ActiveRecord
+        if defined?(::ActiveRecord::Base)
+          require 'sidekiq/middleware/server/active_record'
+          m.add Sidekiq::Middleware::Server::ActiveRecord
+        end
       end
     end