diff --git a/.travis.yml b/.travis.yml
index e40cd1ee8..900b7b656 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -23,6 +23,11 @@ gemfile:
 
 matrix:
   fast_finish: true
+  # Run Danger only once
+  include:
+    - rvm: 2.5
+      gemfile: gemfiles/rails_5_2.gemfile
+      script: bundle exec danger
   exclude:
     - gemfile: gemfiles/rails_5_0.gemfile
       rvm: 2.1
diff --git a/Dangerfile b/Dangerfile
new file mode 100644
index 000000000..d10260cba
--- /dev/null
+++ b/Dangerfile
@@ -0,0 +1,57 @@
+CHANGELOG_FILE = 'NEWS.md'
+GITHUB_REPO = 'https://github.com/doorkeeper-gem/doorkeeper'
+
+def changelog_changed?
+  git.modified_files.include?(CHANGELOG_FILE) || git.added_files.include?(CHANGELOG_FILE)
+end
+
+def changelog_entry_example
+  pr_number = github.pr_json['number']
+  pr_url = github.pr_json['html_url']
+  pr_title = github.pr_title
+                   .sub(/[?.!,;]?$/, '')
+                   .capitalize
+
+  "- [##{pr_number}](#{pr_url}): #{pr_title}."
+end
+
+# --------------------------------------------------------------------------------------------------------------------
+# Has any changes happened inside the actual library code?
+# --------------------------------------------------------------------------------------------------------------------
+has_app_changes = !git.modified_files.grep(/lib/).empty?
+has_spec_changes = !git.modified_files.grep(/spec/).empty?
+
+# --------------------------------------------------------------------------------------------------------------------
+# You've made changes to lib, but didn't write any tests?
+# --------------------------------------------------------------------------------------------------------------------
+if has_app_changes && !has_spec_changes
+  warn("There're library changes, but not tests. That's OK as long as you're refactoring existing code.", sticky: false)
+end
+
+# --------------------------------------------------------------------------------------------------------------------
+# You've made changes to specs, but no library code has changed?
+# --------------------------------------------------------------------------------------------------------------------
+if !has_app_changes && has_spec_changes
+  message('We really appreciate pull requests that demonstrate issues, even without a fix. That said, the next step is to try and fix the failing tests!', sticky: false)
+end
+
+# Mainly to encourage writing up some reasoning about the PR, rather than
+# just leaving a title
+if github.pr_body.length < 10
+  fail "Please provide a summary in the Pull Request description"
+end
+
+# --------------------------------------------------------------------------------------------------------------------
+# Have you updated CHANGELOG.md?
+# --------------------------------------------------------------------------------------------------------------------
+# Add a CHANGELOG entry for app changes
+if has_app_changes && !changelog_changed?
+  markdown <<-MARKDOWN
+Here's an example of a #{CHANGELOG_FILE} entry:
+```markdown
+#{changelog_entry_example}
+```
+  MARKDOWN
+
+  fail("Please include a changelog entry. \nYou can find it at [#{CHANGELOG_FILE}](#{GITHUB_REPO}/blob/master/#{CHANGELOG_FILE}).")
+end
diff --git a/NEWS.md b/NEWS.md
index 4ce02a0a7..ce17213cc 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -12,7 +12,8 @@ User-visible changes worth mentioning.
   triggers every time)
 - [#1149] Fix for `URIChecker#valid_for_authorization?` false negative when query is blank, but `?` present.
 - [#1151] Fix Refresh Token strategy: add proper validation of client credentials both for Public & Private clients.
-- [#1152] Fixmigration template: change resource owner data type from integer to references
+- [#1152] Fix migration template: change resource owner data type from integer to Rails generic `references`
+- [#1154] Refactor `StaleRecordsCleaner` to be ORM agnostic.
 
 ## 5.0.0
 
diff --git a/app/controllers/doorkeeper/application_controller.rb b/app/controllers/doorkeeper/application_controller.rb
index e9b4d960f..5d0a10c7d 100644
--- a/app/controllers/doorkeeper/application_controller.rb
+++ b/app/controllers/doorkeeper/application_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   class ApplicationController <
     Doorkeeper.configuration.base_controller.constantize
diff --git a/app/controllers/doorkeeper/application_metal_controller.rb b/app/controllers/doorkeeper/application_metal_controller.rb
index dac3e0d05..167cd210e 100644
--- a/app/controllers/doorkeeper/application_metal_controller.rb
+++ b/app/controllers/doorkeeper/application_metal_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   class ApplicationMetalController < ActionController::Metal
     MODULES = [
diff --git a/app/controllers/doorkeeper/applications_controller.rb b/app/controllers/doorkeeper/applications_controller.rb
index 550368271..e4a2bf914 100644
--- a/app/controllers/doorkeeper/applications_controller.rb
+++ b/app/controllers/doorkeeper/applications_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   class ApplicationsController < Doorkeeper::ApplicationController
     layout 'doorkeeper/admin' unless Doorkeeper.configuration.api_only
diff --git a/app/controllers/doorkeeper/authorizations_controller.rb b/app/controllers/doorkeeper/authorizations_controller.rb
index ddd27677d..21473849e 100644
--- a/app/controllers/doorkeeper/authorizations_controller.rb
+++ b/app/controllers/doorkeeper/authorizations_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   class AuthorizationsController < Doorkeeper::ApplicationController
     before_action :authenticate_resource_owner!
diff --git a/app/controllers/doorkeeper/authorized_applications_controller.rb b/app/controllers/doorkeeper/authorized_applications_controller.rb
index 755106029..d56bd4a95 100644
--- a/app/controllers/doorkeeper/authorized_applications_controller.rb
+++ b/app/controllers/doorkeeper/authorized_applications_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   class AuthorizedApplicationsController < Doorkeeper::ApplicationController
     before_action :authenticate_resource_owner!
diff --git a/app/controllers/doorkeeper/token_info_controller.rb b/app/controllers/doorkeeper/token_info_controller.rb
index 79249d5b7..bdf4ccc73 100644
--- a/app/controllers/doorkeeper/token_info_controller.rb
+++ b/app/controllers/doorkeeper/token_info_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   class TokenInfoController < Doorkeeper::ApplicationMetalController
     def show
diff --git a/app/controllers/doorkeeper/tokens_controller.rb b/app/controllers/doorkeeper/tokens_controller.rb
index af5134c5c..07033d7e0 100644
--- a/app/controllers/doorkeeper/tokens_controller.rb
+++ b/app/controllers/doorkeeper/tokens_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   class TokensController < Doorkeeper::ApplicationMetalController
     def create
diff --git a/app/helpers/doorkeeper/dashboard_helper.rb b/app/helpers/doorkeeper/dashboard_helper.rb
index 5925a2e83..23cedab3f 100644
--- a/app/helpers/doorkeeper/dashboard_helper.rb
+++ b/app/helpers/doorkeeper/dashboard_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module DashboardHelper
     def doorkeeper_errors_for(object, method)
diff --git a/app/validators/redirect_uri_validator.rb b/app/validators/redirect_uri_validator.rb
index 3e56c5533..8e7f0d6dc 100644
--- a/app/validators/redirect_uri_validator.rb
+++ b/app/validators/redirect_uri_validator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'uri'
 
 class RedirectUriValidator < ActiveModel::EachValidator
diff --git a/doorkeeper.gemspec b/doorkeeper.gemspec
index e426cb624..27d46bcec 100644
--- a/doorkeeper.gemspec
+++ b/doorkeeper.gemspec
@@ -2,29 +2,30 @@ $LOAD_PATH.push File.expand_path('../lib', __FILE__)
 
 require 'doorkeeper/version'
 
-Gem::Specification.new do |s|
-  s.name        = 'doorkeeper'
-  s.version     = Doorkeeper.gem_version
-  s.authors     = ['Felipe Elias Philipp', 'Tute Costa', 'Jon Moss', 'Nikita Bulai']
-  s.email       = %w(bulaj.nikita@gmail.com)
-  s.homepage    = 'https://github.com/doorkeeper-gem/doorkeeper'
-  s.summary     = 'OAuth 2 provider for Rails and Grape'
-  s.description = 'Doorkeeper is an OAuth 2 provider for Rails and Grape.'
-  s.license     = 'MIT'
+Gem::Specification.new do |gem|
+  gem.name        = 'doorkeeper'
+  gem.version     = Doorkeeper.gem_version
+  gem.authors     = ['Felipe Elias Philipp', 'Tute Costa', 'Jon Moss', 'Nikita Bulai']
+  gem.email       = %w(bulaj.nikita@gmail.com)
+  gem.homepage    = 'https://github.com/doorkeeper-gem/doorkeeper'
+  gem.summary     = 'OAuth 2 provider for Rails and Grape'
+  gem.description = 'Doorkeeper is an OAuth 2 provider for Rails and Grape.'
+  gem.license     = 'MIT'
 
-  s.files         = `git ls-files`.split("\n")
-  s.test_files    = `git ls-files -- spec/*`.split("\n")
-  s.require_paths = ['lib']
+  gem.files         = `git ls-files`.split("\n")
+  gem.test_files    = `git ls-files -- spec/*`.split("\n")
+  gem.require_paths = ['lib']
 
-  s.add_dependency 'railties', '>= 4.2'
-  s.required_ruby_version = '>= 2.1'
+  gem.add_dependency 'railties', '>= 4.2'
+  gem.required_ruby_version = '>= 2.1'
 
-  s.add_development_dependency 'capybara', '~> 2.18'
-  s.add_development_dependency 'coveralls'
-  s.add_development_dependency 'grape'
-  s.add_development_dependency 'database_cleaner', '~> 1.6'
-  s.add_development_dependency 'factory_bot', '~> 4.8'
-  s.add_development_dependency 'generator_spec', '~> 0.9.3'
-  s.add_development_dependency 'rake', '>= 11.3.0'
-  s.add_development_dependency 'rspec-rails'
+  gem.add_development_dependency 'capybara', '~> 2.18'
+  gem.add_development_dependency 'coveralls'
+  gem.add_development_dependency 'danger', '~> 5.0'
+  gem.add_development_dependency 'grape'
+  gem.add_development_dependency 'database_cleaner', '~> 1.6'
+  gem.add_development_dependency 'factory_bot', '~> 4.8'
+  gem.add_development_dependency 'generator_spec', '~> 0.9.3'
+  gem.add_development_dependency 'rake', '>= 11.3.0'
+  gem.add_development_dependency 'rspec-rails'
 end
diff --git a/lib/doorkeeper.rb b/lib/doorkeeper.rb
index d20966614..348c67ece 100644
--- a/lib/doorkeeper.rb
+++ b/lib/doorkeeper.rb
@@ -67,6 +67,7 @@
 require 'doorkeeper/rails/helpers'
 
 require 'doorkeeper/rake'
+require 'doorkeeper/stale_records_cleaner'
 
 require 'doorkeeper/orm/active_record'
 
diff --git a/lib/doorkeeper/engine.rb b/lib/doorkeeper/engine.rb
index 4834d2b43..6da4ab711 100644
--- a/lib/doorkeeper/engine.rb
+++ b/lib/doorkeeper/engine.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   class Engine < Rails::Engine
     initializer "doorkeeper.params.filter" do |app|
diff --git a/lib/doorkeeper/errors.rb b/lib/doorkeeper/errors.rb
index ca28dac95..0a73f3a85 100644
--- a/lib/doorkeeper/errors.rb
+++ b/lib/doorkeeper/errors.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Errors
     class DoorkeeperError < StandardError
@@ -46,6 +48,7 @@ def initialize(response)
 
     UnableToGenerateToken = Class.new(DoorkeeperError)
     TokenGeneratorNotFound = Class.new(DoorkeeperError)
+    NoOrmCleaner = Class.new(DoorkeeperError)
 
     InvalidToken = Class.new BaseResponseError
     TokenExpired = Class.new InvalidToken
diff --git a/lib/doorkeeper/grape/authorization_decorator.rb b/lib/doorkeeper/grape/authorization_decorator.rb
index f5b71a398..414fc4156 100644
--- a/lib/doorkeeper/grape/authorization_decorator.rb
+++ b/lib/doorkeeper/grape/authorization_decorator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Grape
     class AuthorizationDecorator < SimpleDelegator
diff --git a/lib/doorkeeper/grape/helpers.rb b/lib/doorkeeper/grape/helpers.rb
index 0ed73e8bc..31da6b1f1 100644
--- a/lib/doorkeeper/grape/helpers.rb
+++ b/lib/doorkeeper/grape/helpers.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'doorkeeper/grape/authorization_decorator'
 
 module Doorkeeper
diff --git a/lib/doorkeeper/helpers/controller.rb b/lib/doorkeeper/helpers/controller.rb
index ea3449529..e71a4f319 100644
--- a/lib/doorkeeper/helpers/controller.rb
+++ b/lib/doorkeeper/helpers/controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Define methods that can be called in any controller that inherits from
 # Doorkeeper::ApplicationMetalController or Doorkeeper::ApplicationController
 module Doorkeeper
diff --git a/lib/doorkeeper/models/access_grant_mixin.rb b/lib/doorkeeper/models/access_grant_mixin.rb
index 2665db1bc..e016b28e5 100644
--- a/lib/doorkeeper/models/access_grant_mixin.rb
+++ b/lib/doorkeeper/models/access_grant_mixin.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module AccessGrantMixin
     extend ActiveSupport::Concern
diff --git a/lib/doorkeeper/models/access_token_mixin.rb b/lib/doorkeeper/models/access_token_mixin.rb
index 71dcb611b..098d6ed98 100644
--- a/lib/doorkeeper/models/access_token_mixin.rb
+++ b/lib/doorkeeper/models/access_token_mixin.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module AccessTokenMixin
     extend ActiveSupport::Concern
diff --git a/lib/doorkeeper/models/application_mixin.rb b/lib/doorkeeper/models/application_mixin.rb
index 10c871610..a8bfdd994 100644
--- a/lib/doorkeeper/models/application_mixin.rb
+++ b/lib/doorkeeper/models/application_mixin.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module ApplicationMixin
     extend ActiveSupport::Concern
diff --git a/lib/doorkeeper/models/concerns/accessible.rb b/lib/doorkeeper/models/concerns/accessible.rb
index f2f0044f9..a0bc125f6 100644
--- a/lib/doorkeeper/models/concerns/accessible.rb
+++ b/lib/doorkeeper/models/concerns/accessible.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Models
     module Accessible
diff --git a/lib/doorkeeper/models/concerns/expirable.rb b/lib/doorkeeper/models/concerns/expirable.rb
index 541a09931..2b7721294 100644
--- a/lib/doorkeeper/models/concerns/expirable.rb
+++ b/lib/doorkeeper/models/concerns/expirable.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Models
     module Expirable
diff --git a/lib/doorkeeper/models/concerns/orderable.rb b/lib/doorkeeper/models/concerns/orderable.rb
index 072c8c42c..6d5938839 100644
--- a/lib/doorkeeper/models/concerns/orderable.rb
+++ b/lib/doorkeeper/models/concerns/orderable.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Models
     module Orderable
diff --git a/lib/doorkeeper/models/concerns/ownership.rb b/lib/doorkeeper/models/concerns/ownership.rb
index 535e4622b..22ab88493 100644
--- a/lib/doorkeeper/models/concerns/ownership.rb
+++ b/lib/doorkeeper/models/concerns/ownership.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Models
     module Ownership
diff --git a/lib/doorkeeper/models/concerns/revocable.rb b/lib/doorkeeper/models/concerns/revocable.rb
index fac80c217..24159c9f6 100644
--- a/lib/doorkeeper/models/concerns/revocable.rb
+++ b/lib/doorkeeper/models/concerns/revocable.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Models
     module Revocable
diff --git a/lib/doorkeeper/models/concerns/scopes.rb b/lib/doorkeeper/models/concerns/scopes.rb
index 8d0788c11..4f475dcb4 100644
--- a/lib/doorkeeper/models/concerns/scopes.rb
+++ b/lib/doorkeeper/models/concerns/scopes.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Models
     module Scopes
diff --git a/lib/doorkeeper/oauth/authorization/code.rb b/lib/doorkeeper/oauth/authorization/code.rb
index 960662e5e..73e631f5a 100644
--- a/lib/doorkeeper/oauth/authorization/code.rb
+++ b/lib/doorkeeper/oauth/authorization/code.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     module Authorization
diff --git a/lib/doorkeeper/oauth/authorization/context.rb b/lib/doorkeeper/oauth/authorization/context.rb
index 1281d576e..b0524214b 100644
--- a/lib/doorkeeper/oauth/authorization/context.rb
+++ b/lib/doorkeeper/oauth/authorization/context.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     module Authorization
diff --git a/lib/doorkeeper/oauth/authorization/token.rb b/lib/doorkeeper/oauth/authorization/token.rb
index e881df4c4..a022b926c 100644
--- a/lib/doorkeeper/oauth/authorization/token.rb
+++ b/lib/doorkeeper/oauth/authorization/token.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     module Authorization
diff --git a/lib/doorkeeper/oauth/authorization/uri_builder.rb b/lib/doorkeeper/oauth/authorization/uri_builder.rb
index d8546aa42..bb6ce20fd 100644
--- a/lib/doorkeeper/oauth/authorization/uri_builder.rb
+++ b/lib/doorkeeper/oauth/authorization/uri_builder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rack/utils'
 
 module Doorkeeper
diff --git a/lib/doorkeeper/oauth/authorization_code_request.rb b/lib/doorkeeper/oauth/authorization_code_request.rb
index f4c3eed45..b93fac8c7 100644
--- a/lib/doorkeeper/oauth/authorization_code_request.rb
+++ b/lib/doorkeeper/oauth/authorization_code_request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class AuthorizationCodeRequest < BaseRequest
diff --git a/lib/doorkeeper/oauth/base_request.rb b/lib/doorkeeper/oauth/base_request.rb
index 636e42346..573b128e4 100644
--- a/lib/doorkeeper/oauth/base_request.rb
+++ b/lib/doorkeeper/oauth/base_request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class BaseRequest
diff --git a/lib/doorkeeper/oauth/base_response.rb b/lib/doorkeeper/oauth/base_response.rb
index dd7c1bebd..84c29f640 100644
--- a/lib/doorkeeper/oauth/base_response.rb
+++ b/lib/doorkeeper/oauth/base_response.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class BaseResponse
diff --git a/lib/doorkeeper/oauth/client.rb b/lib/doorkeeper/oauth/client.rb
index d8ce77e17..3a31b0531 100644
--- a/lib/doorkeeper/oauth/client.rb
+++ b/lib/doorkeeper/oauth/client.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class Client
diff --git a/lib/doorkeeper/oauth/client/credentials.rb b/lib/doorkeeper/oauth/client/credentials.rb
index 62cc8dac5..d9b69e4c7 100644
--- a/lib/doorkeeper/oauth/client/credentials.rb
+++ b/lib/doorkeeper/oauth/client/credentials.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class Client
diff --git a/lib/doorkeeper/oauth/client_credentials/creator.rb b/lib/doorkeeper/oauth/client_credentials/creator.rb
index 09ad284d5..287c979b8 100644
--- a/lib/doorkeeper/oauth/client_credentials/creator.rb
+++ b/lib/doorkeeper/oauth/client_credentials/creator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class ClientCredentialsRequest < BaseRequest
diff --git a/lib/doorkeeper/oauth/client_credentials/issuer.rb b/lib/doorkeeper/oauth/client_credentials/issuer.rb
index 7c8edaf57..f9bb67b13 100644
--- a/lib/doorkeeper/oauth/client_credentials/issuer.rb
+++ b/lib/doorkeeper/oauth/client_credentials/issuer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class ClientCredentialsRequest < BaseRequest
diff --git a/lib/doorkeeper/oauth/client_credentials/validation.rb b/lib/doorkeeper/oauth/client_credentials/validation.rb
index 964f97b89..fadd62933 100644
--- a/lib/doorkeeper/oauth/client_credentials/validation.rb
+++ b/lib/doorkeeper/oauth/client_credentials/validation.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class ClientCredentialsRequest < BaseRequest
diff --git a/lib/doorkeeper/oauth/client_credentials_request.rb b/lib/doorkeeper/oauth/client_credentials_request.rb
index f9df39d65..05422b078 100644
--- a/lib/doorkeeper/oauth/client_credentials_request.rb
+++ b/lib/doorkeeper/oauth/client_credentials_request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class ClientCredentialsRequest < BaseRequest
diff --git a/lib/doorkeeper/oauth/code_request.rb b/lib/doorkeeper/oauth/code_request.rb
index a81f4b8c7..b7583dcaa 100644
--- a/lib/doorkeeper/oauth/code_request.rb
+++ b/lib/doorkeeper/oauth/code_request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class CodeRequest
diff --git a/lib/doorkeeper/oauth/code_response.rb b/lib/doorkeeper/oauth/code_response.rb
index 83cc32f19..cf193c931 100644
--- a/lib/doorkeeper/oauth/code_response.rb
+++ b/lib/doorkeeper/oauth/code_response.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class CodeResponse < BaseResponse
diff --git a/lib/doorkeeper/oauth/error.rb b/lib/doorkeeper/oauth/error.rb
index 93505ccf5..a6c99fb0f 100644
--- a/lib/doorkeeper/oauth/error.rb
+++ b/lib/doorkeeper/oauth/error.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     Error = Struct.new(:name, :state) do
diff --git a/lib/doorkeeper/oauth/error_response.rb b/lib/doorkeeper/oauth/error_response.rb
index 1fb7549ff..afcc561aa 100644
--- a/lib/doorkeeper/oauth/error_response.rb
+++ b/lib/doorkeeper/oauth/error_response.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class ErrorResponse < BaseResponse
diff --git a/lib/doorkeeper/oauth/forbidden_token_response.rb b/lib/doorkeeper/oauth/forbidden_token_response.rb
index d87ce0aae..ed004d4c2 100644
--- a/lib/doorkeeper/oauth/forbidden_token_response.rb
+++ b/lib/doorkeeper/oauth/forbidden_token_response.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class ForbiddenTokenResponse < ErrorResponse
diff --git a/lib/doorkeeper/oauth/helpers/scope_checker.rb b/lib/doorkeeper/oauth/helpers/scope_checker.rb
index 3cf853e08..c1754eceb 100644
--- a/lib/doorkeeper/oauth/helpers/scope_checker.rb
+++ b/lib/doorkeeper/oauth/helpers/scope_checker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     module Helpers
diff --git a/lib/doorkeeper/oauth/helpers/unique_token.rb b/lib/doorkeeper/oauth/helpers/unique_token.rb
index f506a85da..13f012596 100644
--- a/lib/doorkeeper/oauth/helpers/unique_token.rb
+++ b/lib/doorkeeper/oauth/helpers/unique_token.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     module Helpers
diff --git a/lib/doorkeeper/oauth/helpers/uri_checker.rb b/lib/doorkeeper/oauth/helpers/uri_checker.rb
index eda3d3859..7cb7f1db2 100644
--- a/lib/doorkeeper/oauth/helpers/uri_checker.rb
+++ b/lib/doorkeeper/oauth/helpers/uri_checker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     module Helpers
diff --git a/lib/doorkeeper/oauth/invalid_token_response.rb b/lib/doorkeeper/oauth/invalid_token_response.rb
index 8e507f95c..8034d169e 100644
--- a/lib/doorkeeper/oauth/invalid_token_response.rb
+++ b/lib/doorkeeper/oauth/invalid_token_response.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class InvalidTokenResponse < ErrorResponse
diff --git a/lib/doorkeeper/oauth/password_access_token_request.rb b/lib/doorkeeper/oauth/password_access_token_request.rb
index 5f6aac605..9d2b088fd 100644
--- a/lib/doorkeeper/oauth/password_access_token_request.rb
+++ b/lib/doorkeeper/oauth/password_access_token_request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class PasswordAccessTokenRequest < BaseRequest
diff --git a/lib/doorkeeper/oauth/pre_authorization.rb b/lib/doorkeeper/oauth/pre_authorization.rb
index 9ec0a1a69..64a22bb35 100644
--- a/lib/doorkeeper/oauth/pre_authorization.rb
+++ b/lib/doorkeeper/oauth/pre_authorization.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class PreAuthorization
diff --git a/lib/doorkeeper/oauth/refresh_token_request.rb b/lib/doorkeeper/oauth/refresh_token_request.rb
index af80850d2..b033131d4 100644
--- a/lib/doorkeeper/oauth/refresh_token_request.rb
+++ b/lib/doorkeeper/oauth/refresh_token_request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class RefreshTokenRequest < BaseRequest
diff --git a/lib/doorkeeper/oauth/scopes.rb b/lib/doorkeeper/oauth/scopes.rb
index 5da0a5342..1865c621c 100644
--- a/lib/doorkeeper/oauth/scopes.rb
+++ b/lib/doorkeeper/oauth/scopes.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class Scopes
diff --git a/lib/doorkeeper/oauth/token.rb b/lib/doorkeeper/oauth/token.rb
index 36fb581b8..c3a9d672f 100644
--- a/lib/doorkeeper/oauth/token.rb
+++ b/lib/doorkeeper/oauth/token.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class Token
diff --git a/lib/doorkeeper/oauth/token_introspection.rb b/lib/doorkeeper/oauth/token_introspection.rb
index 26a63de48..a87371ccd 100644
--- a/lib/doorkeeper/oauth/token_introspection.rb
+++ b/lib/doorkeeper/oauth/token_introspection.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     # RFC7662 OAuth 2.0 Token Introspection
diff --git a/lib/doorkeeper/oauth/token_request.rb b/lib/doorkeeper/oauth/token_request.rb
index 9908c23ef..b8aa38429 100644
--- a/lib/doorkeeper/oauth/token_request.rb
+++ b/lib/doorkeeper/oauth/token_request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class TokenRequest
diff --git a/lib/doorkeeper/oauth/token_response.rb b/lib/doorkeeper/oauth/token_response.rb
index 93f6bbe7e..aa3c31119 100644
--- a/lib/doorkeeper/oauth/token_response.rb
+++ b/lib/doorkeeper/oauth/token_response.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module OAuth
     class TokenResponse
diff --git a/lib/doorkeeper/orm/active_record.rb b/lib/doorkeeper/orm/active_record.rb
index 5cda5f1ab..0cbb4f94b 100644
--- a/lib/doorkeeper/orm/active_record.rb
+++ b/lib/doorkeeper/orm/active_record.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'active_support/lazy_load_hooks'
 
 require 'doorkeeper/orm/active_record/stale_records_cleaner'
diff --git a/lib/doorkeeper/rails/helpers.rb b/lib/doorkeeper/rails/helpers.rb
index 780bcf5cd..70c9b0148 100644
--- a/lib/doorkeeper/rails/helpers.rb
+++ b/lib/doorkeeper/rails/helpers.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Rails
     module Helpers
diff --git a/lib/doorkeeper/rails/routes.rb b/lib/doorkeeper/rails/routes.rb
index a44b2df99..cd88e4139 100644
--- a/lib/doorkeeper/rails/routes.rb
+++ b/lib/doorkeeper/rails/routes.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'doorkeeper/rails/routes/mapping'
 require 'doorkeeper/rails/routes/mapper'
 
diff --git a/lib/doorkeeper/rails/routes/mapper.rb b/lib/doorkeeper/rails/routes/mapper.rb
index bfee19b52..7ec5fd75b 100644
--- a/lib/doorkeeper/rails/routes/mapper.rb
+++ b/lib/doorkeeper/rails/routes/mapper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Rails
     class Routes # :nodoc:
diff --git a/lib/doorkeeper/rails/routes/mapping.rb b/lib/doorkeeper/rails/routes/mapping.rb
index d2f129ce1..71b543972 100644
--- a/lib/doorkeeper/rails/routes/mapping.rb
+++ b/lib/doorkeeper/rails/routes/mapping.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Rails
     class Routes # :nodoc:
diff --git a/lib/doorkeeper/rake/db.rake b/lib/doorkeeper/rake/db.rake
index f3dd5f0af..caaa7bb27 100644
--- a/lib/doorkeeper/rake/db.rake
+++ b/lib/doorkeeper/rake/db.rake
@@ -13,26 +13,26 @@ namespace :doorkeeper do
     namespace :cleanup do
       desc 'Removes stale access tokens'
       task revoked_tokens: 'doorkeeper:setup' do
-        cleaner = Doorkeeper::Orm::ActiveRecord::StaleRecordsCleaner.new(Doorkeeper::AccessToken)
+        cleaner = Doorkeeper::StaleRecordsCleaner.new(Doorkeeper::AccessToken)
         cleaner.clean_revoked
       end
 
       desc 'Removes expired (TTL passed) access tokens'
       task expired_tokens: 'doorkeeper:setup' do
         expirable_tokens = Doorkeeper::AccessToken.where(refresh_token: nil)
-        cleaner = Doorkeeper::Orm::ActiveRecord::StaleRecordsCleaner.new(expirable_tokens)
+        cleaner = Doorkeeper::StaleRecordsCleaner.new(expirable_tokens)
         cleaner.clean_expired(Doorkeeper.configuration.access_token_expires_in)
       end
 
       desc 'Removes stale access grants'
       task revoked_grants: 'doorkeeper:setup' do
-        cleaner = Doorkeeper::Orm::ActiveRecord::StaleRecordsCleaner.new(Doorkeeper::AccessGrant)
+        cleaner = Doorkeeper::StaleRecordsCleaner.new(Doorkeeper::AccessGrant)
         cleaner.clean_revoked
       end
 
       desc 'Removes expired (TTL passed) access grants'
       task expired_grants: 'doorkeeper:setup' do
-        cleaner = Doorkeeper::Orm::ActiveRecord::StaleRecordsCleaner.new(Doorkeeper::AccessGrant)
+        cleaner = Doorkeeper::StaleRecordsCleaner.new(Doorkeeper::AccessGrant)
         cleaner.clean_expired(Doorkeeper.configuration.authorization_code_expires_in)
       end
     end
diff --git a/lib/doorkeeper/request.rb b/lib/doorkeeper/request.rb
index f1b231762..e8366b651 100644
--- a/lib/doorkeeper/request.rb
+++ b/lib/doorkeeper/request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Request
     class << self
diff --git a/lib/doorkeeper/request/authorization_code.rb b/lib/doorkeeper/request/authorization_code.rb
index 51cf3abe5..d4a46a3ee 100644
--- a/lib/doorkeeper/request/authorization_code.rb
+++ b/lib/doorkeeper/request/authorization_code.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Request
     class AuthorizationCode < Strategy
diff --git a/lib/doorkeeper/request/client_credentials.rb b/lib/doorkeeper/request/client_credentials.rb
index d05f39916..00d89ff3d 100644
--- a/lib/doorkeeper/request/client_credentials.rb
+++ b/lib/doorkeeper/request/client_credentials.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Request
     class ClientCredentials < Strategy
diff --git a/lib/doorkeeper/request/code.rb b/lib/doorkeeper/request/code.rb
index 39782b0f2..d4cadb5d0 100644
--- a/lib/doorkeeper/request/code.rb
+++ b/lib/doorkeeper/request/code.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Request
     class Code < Strategy
diff --git a/lib/doorkeeper/request/password.rb b/lib/doorkeeper/request/password.rb
index 9ee966424..4f1379d2c 100644
--- a/lib/doorkeeper/request/password.rb
+++ b/lib/doorkeeper/request/password.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Request
     class Password < Strategy
diff --git a/lib/doorkeeper/request/refresh_token.rb b/lib/doorkeeper/request/refresh_token.rb
index cfc5ace52..c47ce6b14 100644
--- a/lib/doorkeeper/request/refresh_token.rb
+++ b/lib/doorkeeper/request/refresh_token.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Request
     class RefreshToken < Strategy
diff --git a/lib/doorkeeper/request/strategy.rb b/lib/doorkeeper/request/strategy.rb
index ecf6f4157..a4f379ba8 100644
--- a/lib/doorkeeper/request/strategy.rb
+++ b/lib/doorkeeper/request/strategy.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Request
     class Strategy
diff --git a/lib/doorkeeper/request/token.rb b/lib/doorkeeper/request/token.rb
index 93528d992..4e609835d 100644
--- a/lib/doorkeeper/request/token.rb
+++ b/lib/doorkeeper/request/token.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Request
     class Token < Strategy
diff --git a/lib/doorkeeper/server.rb b/lib/doorkeeper/server.rb
index 697c2d903..2fa8fadea 100644
--- a/lib/doorkeeper/server.rb
+++ b/lib/doorkeeper/server.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   class Server
     attr_accessor :context
diff --git a/lib/doorkeeper/stale_records_cleaner.rb b/lib/doorkeeper/stale_records_cleaner.rb
new file mode 100644
index 000000000..45c2b5669
--- /dev/null
+++ b/lib/doorkeeper/stale_records_cleaner.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+module Doorkeeper
+  class StaleRecordsCleaner
+    CLEANER_CLASS = 'StaleRecordsCleaner'.freeze
+
+    def self.for(base_scope)
+      orm_adapter = "doorkeeper/orm/#{Doorkeeper.configuration.orm}".classify
+
+      orm_cleaner = "#{orm_adapter}::#{CLEANER_CLASS}".constantize
+      orm_cleaner.new(base_scope)
+    rescue NameError
+      raise NoOrmCleaner, "'#{Doorkeeper.configuration.orm}' ORM has no cleaner!"
+    end
+
+    def self.new(base_scope)
+      self.for(base_scope)
+    end
+  end
+end
diff --git a/lib/doorkeeper/validations.rb b/lib/doorkeeper/validations.rb
index 1fe8e5bab..d82ced79e 100644
--- a/lib/doorkeeper/validations.rb
+++ b/lib/doorkeeper/validations.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   module Validations
     extend ActiveSupport::Concern
diff --git a/lib/doorkeeper/version.rb b/lib/doorkeeper/version.rb
index af5e4cecc..5f2da8dad 100644
--- a/lib/doorkeeper/version.rb
+++ b/lib/doorkeeper/version.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Doorkeeper
   def self.gem_version
     Gem::Version.new VERSION::STRING
diff --git a/spec/factories.rb b/spec/factories.rb
index 4c91b355b..719393fce 100644
--- a/spec/factories.rb
+++ b/spec/factories.rb
@@ -2,24 +2,24 @@
   factory :access_grant, class: Doorkeeper::AccessGrant do
     sequence(:resource_owner_id) { |n| n }
     application
-    redirect_uri 'https://app.com/callback'
-    expires_in 100
-    scopes 'public write'
+    redirect_uri { 'https://app.com/callback' }
+    expires_in { 100 }
+    scopes { 'public write' }
   end
 
   factory :access_token, class: Doorkeeper::AccessToken do
     sequence(:resource_owner_id) { |n| n }
     application
-    expires_in 2.hours
+    expires_in { 2.hours }
 
     factory :clientless_access_token do
-      application nil
+      application { nil }
     end
   end
 
   factory :application, class: Doorkeeper::Application do
     sequence(:name) { |n| "Application #{n}" }
-    redirect_uri 'https://app.com/callback'
+    redirect_uri { 'https://app.com/callback' }
   end
 
   # do not name this factory :user, otherwise it will conflict with factories
diff --git a/spec/lib/orm/active_record/stale_records_cleaner_spec.rb b/spec/lib/stale_records_cleaner_spec.rb
similarity index 97%
rename from spec/lib/orm/active_record/stale_records_cleaner_spec.rb
rename to spec/lib/stale_records_cleaner_spec.rb
index 981dabd66..9e35894a7 100644
--- a/spec/lib/orm/active_record/stale_records_cleaner_spec.rb
+++ b/spec/lib/stale_records_cleaner_spec.rb
@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-describe Doorkeeper::Orm::ActiveRecord::StaleRecordsCleaner do
+describe Doorkeeper::StaleRecordsCleaner do
   let(:cleaner) { described_class.new(model) }
   let(:models_by_name) do
     {
diff --git a/spec/requests/flows/authorization_code_spec.rb b/spec/requests/flows/authorization_code_spec.rb
index 5730abf9d..602c7f7e1 100644
--- a/spec/requests/flows/authorization_code_spec.rb
+++ b/spec/requests/flows/authorization_code_spec.rb
@@ -66,7 +66,7 @@
     page.driver.post token_endpoint_url(code: authorization_code, client_id: @client.uid,
                                         redirect_uri: @client.redirect_uri)
 
-    expect(Doorkeeper::AccessToken).not_to exist
+    expect(Doorkeeper::AccessToken.count).to be_zero
 
     should_have_json 'error', 'invalid_client'
   end
diff --git a/spec/support/doorkeeper_rspec.rb b/spec/support/doorkeeper_rspec.rb
index 4b6f90fc1..08ac52ddc 100644
--- a/spec/support/doorkeeper_rspec.rb
+++ b/spec/support/doorkeeper_rspec.rb
@@ -4,7 +4,8 @@ class RSpec
     # Doorkeeper configuration, etc.
     def self.print_configuration_info
       puts <<-INFO.strip_heredoc
-        ====> Doorkeeper ORM = #{Doorkeeper.configuration.orm}
+        ====> Doorkeeper ORM: '#{Doorkeeper.configuration.orm}'
+        ====> Doorkeeper version: #{Doorkeeper.gem_version}
         ====> Rails version: #{::Rails.version}
         ====> Ruby version: #{RUBY_VERSION} on #{RUBY_PLATFORM}
       INFO