cache this

app/finders/conversation_finder.rb

@@ -180,7 +180,9 @@ class ConversationFinder
 
   def conversations_base_query
     @conversations.includes(
-      :taggings, :inbox, { assignee: { avatar_attachment: [:blob] } }, { contact: { avatar_attachment: [:blob] } }, :team, :contact_inbox
+      :taggings, :inbox, { assignee: { avatar_attachment: [:blob] } }, { contact: { avatar_attachment: [:blob] } }, :team, :contact_inbox,
+      { cached_last_message: { attachments: { file_attachment: [:blob] } } },
+      :cached_last_non_activity_message
     )
   end
 

app/jobs/migration/backfill_conversation_cached_message_ids_job.rb

@@ -0,0 +1,22 @@
+class Migration::BackfillConversationCachedMessageIdsJob < ApplicationJob
+  queue_as :low
+
+  def perform
+    Conversation.find_in_batches(batch_size: 1000) do |conversations|
+      conversations.each do |conversation|
+        updates = {}
+
+        last_message = conversation.messages.reorder(created_at: :desc).first
+        updates[:last_message_id] = last_message&.id
+
+        last_incoming = conversation.messages.incoming.reorder(created_at: :desc).first
+        updates[:last_incoming_message_id] = last_incoming&.id
+
+        last_non_activity = conversation.messages.where.not(message_type: :activity).reorder(created_at: :desc).first
+        updates[:last_non_activity_message_id] = last_non_activity&.id
+
+        conversation.update_columns(updates)
+      end
+    end
+  end
+end

app/models/conversation.rb

@@ -105,6 +105,9 @@ class Conversation < ApplicationRecord
   belongs_to :contact_inbox
   belongs_to :team, optional: true
   belongs_to :campaign, optional: true
+  belongs_to :cached_last_message, class_name: 'Message', optional: true, foreign_key: 'last_message_id'
+  belongs_to :cached_last_incoming_message, class_name: 'Message', optional: true, foreign_key: 'last_incoming_message_id'
+  belongs_to :cached_last_non_activity_message, class_name: 'Message', optional: true, foreign_key: 'last_non_activity_message_id'
 
   has_many :mentions, dependent: :destroy_async
   has_many :messages, dependent: :destroy_async, autosave: true

app/models/message.rb

@@ -133,6 +133,7 @@ class Message < ApplicationRecord
   has_many :notifications, as: :primary_actor, dependent: :destroy_async
 
   after_create_commit :execute_after_create_commit_callbacks
+  after_create_commit :update_conversation_cached_message_ids
 
   after_update_commit :dispatch_update_event
   after_commit :reindex_for_search, if: :should_index?, on: [:create, :update]
@@ -422,6 +423,15 @@ class Message < ApplicationRecord
   def reindex_for_search
     reindex(mode: :async)
   end
+
+  def update_conversation_cached_message_ids
+    updates = { last_message_id: id }
+    updates[:last_incoming_message_id] = id if incoming?
+    updates[:last_non_activity_message_id] = id unless activity?
+    # rubocop:disable Rails/SkipsModelValidations
+    conversation.update_columns(updates)
+    # rubocop:enable Rails/SkipsModelValidations
+  end
 end
 
 Message.prepend_mod_with('Message')

app/views/api/v1/conversations/partials/_conversation.json.jbuilder

@@ -27,13 +27,10 @@ json.meta do
 end
 
 json.id conversation.display_id
-if conversation.messages.where(account_id: conversation.account_id).last.blank?
+if conversation.cached_last_message.blank?
   json.messages []
 else
-  json.messages [
-    conversation.messages.where(account_id: conversation.account_id)
-                .includes([{ attachments: [{ file_attachment: [:blob] }] }]).last.try(:push_event_data)
-  ]
+  json.messages [conversation.cached_last_message.push_event_data]
 end
 
 json.account_id conversation.account_id
@@ -54,7 +51,7 @@ json.updated_at conversation.updated_at.to_f
 json.timestamp conversation.last_activity_at.to_i
 json.first_reply_created_at conversation.first_reply_created_at.to_i
 json.unread_count conversation.unread_incoming_messages.count
-json.last_non_activity_message conversation.messages.where(account_id: conversation.account_id).non_activity_messages.first.try(:push_event_data)
+json.last_non_activity_message conversation.cached_last_non_activity_message&.push_event_data
 json.last_activity_at conversation.last_activity_at.to_i
 json.priority conversation.priority
 json.waiting_since conversation.waiting_since.to_i.to_i