From https://once.com/writebook

lib/rails_ext/action_text_has_markdown.rb

@@ -0,0 +1,40 @@
+module ActionText
+  module HasMarkdown
+    extend ActiveSupport::Concern
+
+    class_methods do
+      def has_markdown(name, strict_loading: strict_loading_by_default)
+        class_eval <<-CODE, __FILE__, __LINE__ + 1
+          def #{name}
+            markdown_#{name} || build_markdown_#{name}
+          end
+
+          def #{name}?
+            markdown_#{name}.present?
+          end
+
+          def #{name}=(content)
+            self.#{name}.content = content
+          end
+        CODE
+
+        has_one :"markdown_#{name}", -> { where(name: name) },
+          class_name: "ActionText::Markdown", as: :record, inverse_of: :record, autosave: true, dependent: :destroy,
+          strict_loading: strict_loading
+
+        scope :"with_markdown_#{name}", -> { includes("markdown_#{name}") }
+        scope :"with_markdown_#{name}_and_embeds", -> { includes("markdown_#{name}": { embeds_attachments: :blob }) }
+      end
+    end
+
+    def safe_markdown_attribute(name)
+      if self.class.reflect_on_association("markdown_#{name}")&.klass == ActionText::Markdown
+        public_send(name)
+      end
+    end
+  end
+end
+
+ActiveSupport.on_load :active_record do
+  include ActionText::HasMarkdown
+end