Perf improvement by not creating AR objects

Author: amatsuda

app/models/message.rb

@@ -32,18 +32,18 @@ def from_mail(mail, list, list_seq)
       message_id = mail.message_id&.encode Encoding::UTF_8, invalid: :replace, undef: :replace
 
       # mail.in_reply_to returns strange Array object in some cases (?), so let's use the raw value
-      parent_message_id = extract_message_id_from_in_reply_to(mail.header[:in_reply_to]&.value)
-      parent_message = Message.find_by message_id_header: parent_message_id if parent_message_id
-      if !parent_message && (String === mail.references)
-        parent_message = Message.find_by message_id_header: mail.references
+      parent_message_id_header = extract_message_id_from_in_reply_to(mail.header[:in_reply_to]&.value)
+      parent_message_id = Message.where(message_id_header: parent_message_id_header).pick(:id) if parent_message_id_header
+      if !parent_message_id && (String === mail.references)
+        parent_message_id = Message.where(message_id_header: mail.references).pick(:id)
       end
-      if !parent_message && (Array === mail.references)
+      if !parent_message_id && (Array === mail.references)
         mail.references.compact.each do |ref|
-          break if (parent_message = Message.find_by message_id_header: ref)
+          break if (parent_message_id = Message.where(message_id_header: ref).pick(:id))
         end
       end
 
-      new list_id: list.id, list_seq: list_seq, body: body, subject: subject, from: from, published_at: mail.date, message_id_header: message_id, parent_id: parent_message&.id
+      new list_id: list.id, list_seq: list_seq, body: body, subject: subject, from: from, published_at: mail.date, message_id_header: message_id, parent_id: parent_message_id
     end
 
     private def extract_message_id_from_in_reply_to(header)