Improve ActiveStorageLoader example for STI models

examples/active_storage_loader_sti.rb

@@ -0,0 +1,90 @@
+####
+# This is a loader for Active Storage attachments,
+# a little bit more complex than the `active_storage_loader.rb` example
+# because it supports STI (Single Table Inheritance) models where the
+# `has_one_attached` or `has_many_attached` is defined on any of the ancestor classes of the model.
+
+####
+# The model with an attached image and many attached pictures:
+####
+
+# class Event < ApplicationRecord
+# has_one_attached :image
+# has_many_attached :pictures
+# end
+
+####
+# An example data type using the AttachmentLoader:
+####
+
+# class Types::EventType < Types::BaseObject
+# graphql_name 'Event'
+#
+# field :id, ID, null: false
+# field :image, String, null: true
+# field :pictures, String, null: true
+#
+# def image
+# AttachmentLoader.for(:Event, :image).load(object.id).then do |image|
+# Rails.application.routes.url_helpers.url_for(
+# image.variant({ quality: 75 })
+# )
+# end
+# end
+#
+# def pictures
+# AttachmentLoader.for(:Event, :pictures, association_type: :has_many_attached).load(object.id).then do |pictures|
+# pictures.map do |picture|
+# Rails.application.routes.url_helpers.url_for(
+# picture.variant({ quality: 75 })
+# )
+# end
+# end
+# end
+# end
+
+class ActiveStorageLoader < GraphQL::Batch::Loader
+ attr_reader :record_type, :attachment_name, :association_type
+
+ def initialize(record_type, attachment_name, association_type: :has_one_attached)
+ super()
+ @record_type = record_type
+ @attachment_name = attachment_name
+ @association_type = association_type
+ end
+
+ def perform(record_ids)
+ attachments = ActiveStorage::Attachment.includes(:blob, :record).where(
+ record_type: ancestors_record_types, record_id: record_ids, name: attachment_name
+ )
+
+ if @association_type == :has_one_attached
+ attachments.each do |attachment|
+ fulfill(attachment.record_id, attachment)
+ end
+
+ record_ids.each { |id| fulfill(id, nil) unless fulfilled?(id) }
+ else
+ record_ids.each do |record_id|
+ fulfill(record_id, attachments.select { |attachment| attachment.record_id == record_id })
+ end
+ end
+ end
+
+ private
+
+ def ancestors_record_types
+ # Get all ancestor classes of record_type that are descendants of ActiveRecord::Base
+ # This is necessary because in a Single Table Inheritance (STI) setup,
+ # the `has_one_attached` or `has_many_attached`
+ # could be defined on any of the ancestor classes of the model, not just the model itself,
+ # which determines whether the `record_type` string is stored as the model's class name
+ # or the ancestor's class name.
+ # So we for any of the ancestor classes to ensure we don't miss the attachment
+ # we are looking for:
+
+ @record_type.to_s.constantize.ancestors.select do |ancestor|
+ ancestor < ActiveRecord::Base
+ end.map(&:to_s)
+ end
+end