cache classes with dynamically injected custom attributes

lib/api/v3/utilities/custom_field_injector.rb

@@ -65,21 +65,19 @@ module API
 
         class << self
           def create_value_representer(customizable, representer)
-            injector = CustomFieldInjector.new(representer)
-            customizable.available_custom_fields.each do |custom_field|
-              injector.inject_value(custom_field, embed_links: true)
+            new_representer_class_with(representer, customizable) do |injector|
+              customizable.available_custom_fields.each do |custom_field|
+                injector.inject_value(custom_field, embed_links: true)
+              end
             end
-
-            injector.modified_representer_class
           end
 
           def create_schema_representer(customizable, representer)
-            injector = CustomFieldInjector.new(representer)
-            customizable.available_custom_fields.each do |custom_field|
-              injector.inject_schema(custom_field, customized: customizable)
+            new_representer_class_with(representer, customizable) do |injector|
+              customizable.available_custom_fields.each do |custom_field|
+                injector.inject_schema(custom_field, customized: customizable)
+              end
             end
-
-            injector.modified_representer_class
           end
 
           def create_value_representer_for_property_patching(customizable, representer)
@@ -87,12 +85,11 @@ module API
               property_field?(cf)
             }
 
-            injector = CustomFieldInjector.new(representer)
-            property_fields.each do |custom_field|
-              injector.inject_value(custom_field)
+            new_representer_class_with(representer, customizable) do |injector|
+              property_fields.each do |custom_field|
+                injector.inject_value(custom_field)
+              end
             end
-
-            injector.modified_representer_class
           end
 
           def create_value_representer_for_link_patching(customizable, representer)
@@ -100,12 +97,11 @@ module API
               linked_field?(cf)
             }
 
-            injector = CustomFieldInjector.new(representer)
-            linked_fields.each do |custom_field|
-              injector.inject_patchable_link_value(custom_field)
+            new_representer_class_with(representer, customizable) do |injector|
+              linked_fields.each do |custom_field|
+                injector.inject_patchable_link_value(custom_field)
+              end
             end
-
-            injector.modified_representer_class
           end
 
           def linked_field?(custom_field)
@@ -115,10 +111,26 @@ module API
           def property_field?(custom_field)
             !linked_field?(custom_field)
           end
+
+          def new_representer_class_with(representer, customizable, &block)
+            injector = new(representer, customizable)
+
+            block.call injector
+
+            injector.modified_representer_class
+          end
         end
 
-        def initialize(representer_class)
-          @class = Class.new(representer_class)
+        def initialize(representer_class, customizable)
+          @class = Class.new(representer_class) do
+            class << self
+              attr_accessor :customizable
+            end
+          end
+
+          @class.customizable = customizable
+
+          @class
         end
 
         def modified_representer_class

lib/api/v3/work_packages/work_package_collection_representer.rb

@@ -57,6 +57,24 @@ module API
                 current_user: current_user)
         end
 
+        collection :elements,
+                   getter: -> (*) {
+                     generated_classes = ::Hash.new do |hash, work_package|
+                       hit = hash.values.find { |klass|
+                         klass.customizable.type_id == work_package.type_id &&
+                         klass.customizable.project_id == work_package.project_id
+                       }
+
+                       hash[work_package] = hit || element_decorator.create_class(work_package)
+                     end
+
+                     represented.map { |model|
+                       generated_classes[model].new(model, current_user: current_user)
+                     }
+                   },
+                   exec_context: :decorator,
+                   embedded: true
+
         property :groups,
                  exec_context: :decorator,
                  getter: -> (*) {