fix n+1

lib/templates/serialize_for_api.rb

@@ -9,9 +9,17 @@ module Templates
 
     module_function
 
-    def call(template, schema_documents = template.schema_documents, preview_image_attachments = [])
+    def call(template, schema_documents = template.schema_documents.preload(:blob), preview_image_attachments = nil)
       json = template.as_json(SERIALIZE_PARAMS)
 
+      preview_image_attachments ||=
+        ActiveStorage::Attachment.joins(:blob)
+                                 .where(blob: { filename: '0.jpg' })
+                                 .where(record_id: schema_documents.map(&:id),
+                                        record_type: 'ActiveStorage::Attachment',
+                                        name: :preview_images)
+                                 .preload(:blob)
+
       json[:documents] = template.schema.map do |item|
         attachment = schema_documents.find { |e| e.uuid == item['attachment_uuid'] }