diff --git a/.rubocop.yml b/.rubocop.yml
index d808271c..43ccb9f5 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -8,6 +8,39 @@ AllCops:
   DisplayCopNames: true
   DisplayStyleGuide: true
 
+Style/IndentationConsistency:
+  Exclude:
+    - lib/active_model/serializer/adapter/flatten_json.rb
+    - lib/active_model/serializer/adapter/fragment_cache.rb
+    - lib/active_model/serializer/adapter/json.rb
+    - lib/active_model/serializer/adapter/json/fragment_cache.rb
+    - lib/active_model/serializer/adapter/json_api.rb
+    - lib/active_model/serializer/adapter/json_api/fragment_cache.rb
+    - lib/active_model/serializer/adapter/json_api/pagination_links.rb
+    - lib/active_model/serializer/adapter/null.rb
+
+Style/IndentationWidth:
+  Exclude:
+    - lib/active_model/serializer/adapter/flatten_json.rb
+    - lib/active_model/serializer/adapter/fragment_cache.rb
+    - lib/active_model/serializer/adapter/json.rb
+    - lib/active_model/serializer/adapter/json/fragment_cache.rb
+    - lib/active_model/serializer/adapter/json_api.rb
+    - lib/active_model/serializer/adapter/json_api/fragment_cache.rb
+    - lib/active_model/serializer/adapter/json_api/pagination_links.rb
+    - lib/active_model/serializer/adapter/null.rb
+
+Style/AccessModifierIndentation:
+  Exclude:
+    - lib/active_model/serializer/adapter/flatten_json.rb
+    - lib/active_model/serializer/adapter/fragment_cache.rb
+    - lib/active_model/serializer/adapter/json.rb
+    - lib/active_model/serializer/adapter/json/fragment_cache.rb
+    - lib/active_model/serializer/adapter/json_api.rb
+    - lib/active_model/serializer/adapter/json_api/fragment_cache.rb
+    - lib/active_model/serializer/adapter/json_api/pagination_links.rb
+    - lib/active_model/serializer/adapter/null.rb
+
 Lint/NestedMethodDefinition:
   Enabled: false
   Exclude:
@@ -16,9 +49,6 @@ Lint/NestedMethodDefinition:
 Style/StringLiterals:
   EnforcedStyle: single_quotes
 
-Style/SpecialGlobalVars:
-  Enabled: false
-
 Metrics/AbcSize:
   Max: 35 # TODO: Lower to 15
 
diff --git a/lib/active_model/serializable_resource.rb b/lib/active_model/serializable_resource.rb
index feae1e8e..d3565f9a 100644
--- a/lib/active_model/serializable_resource.rb
+++ b/lib/active_model/serializable_resource.rb
@@ -76,7 +76,7 @@ module ActiveModel
     private
 
     ActiveModelSerializers.silence_warnings do
-    attr_reader :resource, :adapter_opts, :serializer_opts
+      attr_reader :resource, :adapter_opts, :serializer_opts
     end
   end
 end
diff --git a/lib/active_model/serializer/adapter.rb b/lib/active_model/serializer/adapter.rb
index 2b9fb350..3797c39e 100644
--- a/lib/active_model/serializer/adapter.rb
+++ b/lib/active_model/serializer/adapter.rb
@@ -5,11 +5,11 @@ module ActiveModel
       ADAPTER_MAP = {}
       private_constant :ADAPTER_MAP if defined?(private_constant)
       extend ActiveSupport::Autoload
-      require 'active_model/serializer/adapter/json'
-      require 'active_model/serializer/adapter/json_api'
-      autoload :FlattenJson
-      autoload :Null
       autoload :FragmentCache
+      autoload :Json
+      autoload :JsonApi
+      autoload :Null
+      autoload :FlattenJson
 
       def self.create(resource, options = {})
         override = options.delete(:adapter)
@@ -60,14 +60,14 @@ module ActiveModel
             register(adapter_name, adapter_class)
             adapter_class
           }
-        rescue ArgumentError
+        rescue ArgumentError => e
           failure_message =
             "Unknown adapter: #{adapter.inspect}. Valid adapters are: #{adapters}"
-          raise UnknownAdapterError, failure_message, $!.backtrace
-        rescue NameError
+          raise UnknownAdapterError, failure_message, e.backtrace
+        rescue NameError => e
           failure_message =
-            "NameError: #{$!.message}. Unknown adapter: #{adapter.inspect}. Valid adapters are: #{adapters}"
-          raise UnknownAdapterError, failure_message, $!.backtrace
+            "NameError: #{e.message}. Unknown adapter: #{adapter.inspect}. Valid adapters are: #{adapters}"
+          raise UnknownAdapterError, failure_message, e.backtrace
         end
 
         # @api private
diff --git a/lib/active_model/serializer/adapter/flatten_json.rb b/lib/active_model/serializer/adapter/flatten_json.rb
index 7ed57034..0c10f3e6 100644
--- a/lib/active_model/serializer/adapter/flatten_json.rb
+++ b/lib/active_model/serializer/adapter/flatten_json.rb
@@ -1,7 +1,4 @@
-module ActiveModel
-  class Serializer
-    class Adapter
-      class FlattenJson < Json
+class ActiveModel::Serializer::Adapter::FlattenJson < ActiveModel::Serializer::Adapter::Json
         def serializable_hash(options = {})
           super
           @result
@@ -13,7 +10,4 @@ module ActiveModel
         def include_meta(json)
           json
         end
-      end
-    end
-  end
 end
diff --git a/lib/active_model/serializer/adapter/fragment_cache.rb b/lib/active_model/serializer/adapter/fragment_cache.rb
index 8463b5a2..13558c08 100644
--- a/lib/active_model/serializer/adapter/fragment_cache.rb
+++ b/lib/active_model/serializer/adapter/fragment_cache.rb
@@ -1,7 +1,4 @@
-module ActiveModel
-  class Serializer
-    class Adapter
-      class FragmentCache
+class ActiveModel::Serializer::Adapter::FragmentCache
         attr_reader :serializer
 
         def initialize(adapter, serializer, options)
@@ -75,7 +72,4 @@ module ActiveModel
         def to_valid_const_name(name)
           name.gsub('::', '_')
         end
-      end
-    end
-  end
 end
diff --git a/lib/active_model/serializer/adapter/json.rb b/lib/active_model/serializer/adapter/json.rb
index b3fa6e9c..2c0b6455 100644
--- a/lib/active_model/serializer/adapter/json.rb
+++ b/lib/active_model/serializer/adapter/json.rb
@@ -1,9 +1,7 @@
-require 'active_model/serializer/adapter/json/fragment_cache'
+class ActiveModel::Serializer::Adapter::Json < ActiveModel::Serializer::Adapter
+        extend ActiveSupport::Autoload
+        autoload :FragmentCache
 
-module ActiveModel
-  class Serializer
-    class Adapter
-      class Json < Adapter
         def serializable_hash(options = nil)
           options ||= {}
           if serializer.respond_to?(:each)
@@ -44,9 +42,6 @@ module ActiveModel
         end
 
         def fragment_cache(cached_hash, non_cached_hash)
-          Json::FragmentCache.new().fragment_cache(cached_hash, non_cached_hash)
+          ActiveModel::Serializer::Adapter::Json::FragmentCache.new().fragment_cache(cached_hash, non_cached_hash)
         end
-      end
-    end
-  end
 end
diff --git a/lib/active_model/serializer/adapter/json/fragment_cache.rb b/lib/active_model/serializer/adapter/json/fragment_cache.rb
index 846a216f..5e687241 100644
--- a/lib/active_model/serializer/adapter/json/fragment_cache.rb
+++ b/lib/active_model/serializer/adapter/json/fragment_cache.rb
@@ -1,14 +1,5 @@
-require 'active_model/serializer/adapter/fragment_cache'
-module ActiveModel
-  class Serializer
-    class Adapter
-      class Json < Adapter
-        class FragmentCache
+class ActiveModel::Serializer::Adapter::Json::FragmentCache
           def fragment_cache(cached_hash, non_cached_hash)
             non_cached_hash.merge cached_hash
           end
-        end
-      end
-    end
-  end
 end
diff --git a/lib/active_model/serializer/adapter/json_api.rb b/lib/active_model/serializer/adapter/json_api.rb
index ac3bf4a1..f273fc65 100644
--- a/lib/active_model/serializer/adapter/json_api.rb
+++ b/lib/active_model/serializer/adapter/json_api.rb
@@ -1,10 +1,8 @@
-require 'active_model/serializer/adapter/json_api/fragment_cache'
-require 'active_model/serializer/adapter/json_api/pagination_links'
+class ActiveModel::Serializer::Adapter::JsonApi < ActiveModel::Serializer::Adapter
+        extend ActiveSupport::Autoload
+        autoload :PaginationLinks
+        autoload :FragmentCache
 
-module ActiveModel
-  class Serializer
-    class Adapter
-      class JsonApi < Adapter
         def initialize(serializer, options = {})
           super
           @hash = { data: [] }
@@ -49,7 +47,7 @@ module ActiveModel
 
         def fragment_cache(cached_hash, non_cached_hash)
           root = false if @options.include?(:include)
-          JsonApi::FragmentCache.new.fragment_cache(root, cached_hash, non_cached_hash)
+          ActiveModel::Serializer::Adapter::JsonApi::FragmentCache.new().fragment_cache(root, cached_hash, non_cached_hash)
         end
 
         private
@@ -62,6 +60,12 @@ module ActiveModel
           end
         end
 
+        def add_relationships(resource, name, serializers)
+          resource[:relationships] ||= {}
+          resource[:relationships][name] ||= { data: [] }
+          resource[:relationships][name][:data] += serializers.map { |serializer| { type: serializer.json_api_type, id: serializer.id.to_s } }
+        end
+
         def resource_identifier_id_for(serializer)
           if serializer.respond_to?(:id)
             serializer.id
@@ -161,8 +165,8 @@ module ActiveModel
           @hash[:links] = add_pagination_links(links, collection, options) if paginated?(collection)
         end
 
-        def add_pagination_links(links, collection, options)
-          pagination_links = JsonApi::PaginationLinks.new(collection, options[:context]).serializable_hash(options)
+        def add_pagination_links(links, resources, options)
+          pagination_links = ActiveModel::Serializer::Adapter::JsonApi::PaginationLinks.new(resources, options[:context]).serializable_hash(options)
           links.update(pagination_links)
         end
 
@@ -171,7 +175,4 @@ module ActiveModel
             collection.respond_to?(:total_pages) &&
             collection.respond_to?(:size)
         end
-      end
-    end
-  end
 end
diff --git a/lib/active_model/serializer/adapter/json_api/fragment_cache.rb b/lib/active_model/serializer/adapter/json_api/fragment_cache.rb
index 070371ac..ab348130 100644
--- a/lib/active_model/serializer/adapter/json_api/fragment_cache.rb
+++ b/lib/active_model/serializer/adapter/json_api/fragment_cache.rb
@@ -1,9 +1,4 @@
-require 'active_model/serializer/adapter/fragment_cache'
-module ActiveModel
-  class Serializer
-    class Adapter
-      class JsonApi < Adapter
-        class FragmentCache
+class ActiveModel::Serializer::Adapter::JsonApi::FragmentCache
           def fragment_cache(root, cached_hash, non_cached_hash)
             hash              = {}
             core_cached       = cached_hash.first
@@ -15,8 +10,4 @@ module ActiveModel
 
             hash.deep_merge no_root_non_cache.deep_merge no_root_cache
           end
-        end
-      end
-    end
-  end
 end
diff --git a/lib/active_model/serializer/adapter/json_api/pagination_links.rb b/lib/active_model/serializer/adapter/json_api/pagination_links.rb
index 55e3280b..8661f3b1 100644
--- a/lib/active_model/serializer/adapter/json_api/pagination_links.rb
+++ b/lib/active_model/serializer/adapter/json_api/pagination_links.rb
@@ -1,8 +1,4 @@
-module ActiveModel
-  class Serializer
-    class Adapter
-      class JsonApi < Adapter
-        class PaginationLinks
+class ActiveModel::Serializer::Adapter::JsonApi::PaginationLinks
           FIRST_PAGE = 1
 
           attr_reader :collection, :context
@@ -51,8 +47,4 @@ module ActiveModel
           def query_parameters
             @query_parameters ||= context.query_parameters
           end
-        end
-      end
-    end
-  end
 end
diff --git a/lib/active_model/serializer/adapter/null.rb b/lib/active_model/serializer/adapter/null.rb
index 1728f88e..78f9b8e3 100644
--- a/lib/active_model/serializer/adapter/null.rb
+++ b/lib/active_model/serializer/adapter/null.rb
@@ -1,11 +1,5 @@
-module ActiveModel
-  class Serializer
-    class Adapter
-      class Null < Adapter
+class ActiveModel::Serializer::Adapter::Null < ActiveModel::Serializer::Adapter
         def serializable_hash(options = nil)
           {}
         end
-      end
-    end
-  end
 end
diff --git a/lib/active_model/serializer/fieldset.rb b/lib/active_model/serializer/fieldset.rb
index 30e68334..935aea81 100644
--- a/lib/active_model/serializer/fieldset.rb
+++ b/lib/active_model/serializer/fieldset.rb
@@ -18,7 +18,7 @@ module ActiveModel
       private
 
       ActiveModelSerializers.silence_warnings do
-      attr_reader :raw_fields, :root
+        attr_reader :raw_fields, :root
       end
 
       def parsed_fields
diff --git a/test/action_controller/serialization_scope_name_test.rb b/test/action_controller/serialization_scope_name_test.rb
index 6e2b15e6..51abf108 100644
--- a/test/action_controller/serialization_scope_name_test.rb
+++ b/test/action_controller/serialization_scope_name_test.rb
@@ -25,7 +25,7 @@ class DefaultScopeNameTest < ActionController::TestCase
     end
   end
 
- tests UserTestController
+  tests UserTestController
 
   def test_default_scope_name
     get :render_new_user
diff --git a/test/serializers/adapter_for_test.rb b/test/serializers/adapter_for_test.rb
index c55c3a9e..b246b404 100644
--- a/test/serializers/adapter_for_test.rb
+++ b/test/serializers/adapter_for_test.rb
@@ -5,6 +5,11 @@ module ActiveModel
 
       def setup
         @previous_adapter = ActiveModel::Serializer.config.adapter
+        # Eager load adapters
+        ActiveModel::Serializer::Adapter.eager_load!
+        [:json_api, :flatten_json, :null, :json].each do |adapter_name|
+          ActiveModel::Serializer::Adapter.lookup(adapter_name)
+        end
       end
 
       def teardown
diff --git a/test/test_helper.rb b/test/test_helper.rb
index c523041d..e6ba0dff 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -39,15 +39,6 @@ else
 end
 
 require 'active_model_serializers'
-# eager load autoloaded adapters
-# rubocop:disable Lint/Void
-require 'active_model/serializer/adapter'
-ActiveModel::Serializer::Adapter::Null
-ActiveModel::Serializer::Adapter::Json
-ActiveModel::Serializer::Adapter::FlattenJson
-ActiveModel::Serializer::Adapter::JsonApi
-# rubocop:enable Lint/Void
-require 'active_model/serializer/adapter'
 
 require 'support/stream_capture'