Move ApiObject to JsonApi namespace/folder

Follow up to
https://github.com/rails-api/active_model_serializers/pull/1504/files#r52796473.
Moved the Relationship and ResourceIdentifier to the JsonApi
namespace/folder and slightly refactored the Relationship code.

lib/active_model/serializer/adapter/json_api.rb

@@ -7,8 +7,9 @@ class JsonApi < Base
         autoload :FragmentCache
         autoload :Link
         autoload :Meta
+        autoload :ResourceIdentifier
+        autoload :Relationship
         autoload :Deserialization
-        require 'active_model/serializer/adapter/json_api/api_objects'
 
         # TODO: if we like this abstraction and other API objects to it,
         # then extract to its own file and require it.
@@ -99,7 +100,7 @@ def resource_objects_for(serializers)
         end
 
         def process_resource(serializer, primary)
-          resource_identifier = ApiObjects::ResourceIdentifier.new(serializer).as_json
+          resource_identifier = ResourceIdentifier.new(serializer).as_json
           return false unless @resource_identifiers.add?(resource_identifier)
 
           resource_object = resource_object_for(serializer)
@@ -135,7 +136,7 @@ def attributes_for(serializer, fields)
 
         def resource_object_for(serializer)
           resource_object = cache_check(serializer) do
-            resource_object = ApiObjects::ResourceIdentifier.new(serializer).as_json
+            resource_object = ResourceIdentifier.new(serializer).as_json
 
             requested_fields = fieldset && fieldset.fields_for(resource_object[:type])
             attributes = attributes_for(serializer, requested_fields)
@@ -159,7 +160,7 @@ def resource_object_for(serializer)
         def relationships_for(serializer, requested_associations)
           include_tree = IncludeTree.from_include_args(requested_associations)
           serializer.associations(include_tree).each_with_object({}) do |association, hash|
-            hash[association.key] = ApiObjects::Relationship.new(
+            hash[association.key] = Relationship.new(
               serializer,
               association.serializer,
               association.options,

lib/active_model/serializer/adapter/json_api/relationship.rb

@@ -0,0 +1,53 @@
+module ActiveModel
+  class Serializer
+    module Adapter
+      class JsonApi
+        class Relationship
+          def initialize(parent_serializer, serializer, options = {}, links = {}, meta = nil)
+            @options = options
+            @data    = data_for(serializer, options)
+            @links   = links_for(parent_serializer, links)
+            @meta    = meta_for(parent_serializer, meta)
+          end
+
+          def as_json
+            hash = {}
+            hash[:data] = data if options[:include_data]
+            links = self.links
+            hash[:links] = links if links.any?
+            meta = self.meta
+            hash[:meta] = meta if meta
+
+            hash
+          end
+
+          protected
+
+          attr_reader :data, :options, :links, :meta
+
+          private
+
+          def links_for(parent_serializer, links)
+            links.each_with_object({}) do |(key, value), hash|
+              hash[key] = Link.new(parent_serializer, value).as_json
+            end
+          end
+
+          def meta_for(parent_serializer, meta)
+            meta.respond_to?(:call) ? parent_serializer.instance_eval(&meta) : meta
+          end
+
+          def data_for(serializer, options)
+            if serializer.respond_to?(:each)
+              serializer.map { |s| ResourceIdentifier.new(s).as_json }
+            elsif options[:virtual_value]
+              options[:virtual_value]
+            elsif serializer && serializer.object
+              ResourceIdentifier.new(serializer).as_json
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/active_model/serializer/adapter/json_api/resource_identifier.rb

@@ -0,0 +1,37 @@
+module ActiveModel
+  class Serializer
+    module Adapter
+      class JsonApi
+        class ResourceIdentifier
+          def initialize(serializer)
+            @id   = id_for(serializer)
+            @type = type_for(serializer)
+          end
+
+          def as_json
+            { id: id, type: type }
+          end
+
+          protected
+
+          attr_reader :id, :type
+
+          private
+
+          def type_for(serializer)
+            return serializer._type if serializer._type
+            if ActiveModelSerializers.config.jsonapi_resource_type == :singular
+              serializer.object.class.model_name.singular
+            else
+              serializer.object.class.model_name.plural
+            end
+          end
+
+          def id_for(serializer)
+            serializer.read_attribute_for_serialization(:id).to_s
+          end
+        end
+      end
+    end
+  end
+end