Add graphql object types

app/graphql/extensions/attachment.rb

@@ -0,0 +1,36 @@
+# references:
+# https://evilmartians.com/chronicles/active-storage-meets-graphql-pt-2-exposing-attachment-urls
+
+module Extensions
+  class Attachment < GraphQL::Schema::FieldExtension
+    attr_reader :attachment_assoc
+
+    def apply
+      # Here we try to define the attachment name:
+      # - it could be set explicitly via extension options
+      # - or we imply that is the same as the field name w/o "_url"
+      # suffix (e.g., "avatar_url" => "avatar")
+      attachment = options&.[](:attachment) || field.original_name.to_s.sub(/_url$/, "")
+
+      # that's the name of the Active Record association
+      @attachment_assoc = "#{attachment}_attachment"
+    end
+
+    # This method resolves (as it states) the field itself
+    # (it's the same as defining a method within a type)
+    def resolve(object:, **_rest)
+      Loaders::Association.for(
+        object.object.class,
+        attachment_assoc => :blob
+      ).load(object.object)
+    end
+
+    # This method is called if the result of the `resolve`
+    # is a lazy value (e.g., a Promise – like in our case)
+    def after_resolve(value:, **_rest)
+      return if value.nil?
+
+      Rails.application.routes.url_helpers.url_for(value)
+    end
+  end
+end