DEV: Add last_message_id to channel and thread (#22488)

Initial migration and changes to models as well as
changing the following services to update last_message_id:

* Chat::MessageCreator
* Chat::RestoreMessage
* Chat::TrashMessage

The data migration will set the `last_message_id` for all existing
threads and channels in the database.

When we query the thread list as well as the channel,
we look at the last message ID for the following:

* Channel - Sorting DM channels, and channel metadata for the list of channels
* Thread - Last reply details for thread indicators and thread list

plugins/chat/lib/chat/channel_fetcher.rb

@@ -88,7 +88,7 @@ module Chat
     def self.secured_public_channel_search(guardian, options = {})
       allowed_channel_ids = generate_allowed_channel_ids_sql(guardian, exclude_dm_channels: true)
 
-      channels = Chat::Channel.includes(chatable: [:topic_only_relative_url])
+      channels = Chat::Channel.includes(:last_message, chatable: [:topic_only_relative_url])
       channels = channels.includes(:chat_channel_archive) if options[:include_archives]
 
       channels =
@@ -179,10 +179,15 @@ module Chat
     def self.secured_direct_message_channels_search(user_id, guardian, options = {})
       query =
         Chat::Channel.strict_loading.includes(
+          last_message: [:uploads],
           chatable: [{ direct_message_users: [user: :user_option] }, :users],
         )
       query = query.includes(chatable: [{ users: :user_status }]) if SiteSetting.enable_user_status
       query = query.joins(:user_chat_channel_memberships)
+      query =
+        query.joins(
+          "LEFT JOIN chat_messages last_message ON last_message.id = chat_channels.last_message_id",
+        )
 
       scoped_channels =
         Chat::Channel
@@ -223,7 +228,7 @@ module Chat
         query
           .where(chatable_type: Chat::Channel.direct_channel_chatable_types)
           .where(chat_channels: { id: scoped_channels })
-          .order(last_message_sent_at: :desc)
+          .order("last_message.created_at DESC NULLS LAST")
 
       channels = query.to_a
       preload_fields =

plugins/chat/lib/chat/message_creator.rb

@@ -63,6 +63,7 @@ module Chat
         @chat_message.attach_uploads(uploads)
         Chat::Draft.where(user_id: @user.id, chat_channel_id: @chat_channel.id).destroy_all
         post_process_resolved_thread
+        update_channel_last_message
         Chat::Publisher.publish_new!(
           @chat_channel,
           @chat_message,
@@ -71,7 +72,6 @@ module Chat
         )
         Jobs.enqueue(Jobs::Chat::ProcessMessage, { chat_message_id: @chat_message.id })
         Chat::Notifier.notify_new(chat_message: @chat_message, timestamp: @chat_message.created_at)
-        @chat_channel.touch(:last_message_sent_at)
         DiscourseEvent.trigger(:chat_message_created, @chat_message, @chat_channel, @user)
       rescue => error
         @error = error
@@ -232,6 +232,7 @@ module Chat
     def post_process_resolved_thread
       return if resolved_thread.blank?
 
+      resolved_thread.update!(last_message: @chat_message)
       resolved_thread.increment_replies_count_cache
       current_user_thread_membership = resolved_thread.add(@user)
       current_user_thread_membership.update!(last_read_message_id: @chat_message.id)
@@ -240,5 +241,10 @@ module Chat
         resolved_thread.add(resolved_thread.original_message_user)
       end
     end
+
+    def update_channel_last_message
+      return if @chat_message.thread_reply?
+      @chat_channel.update!(last_message: @chat_message)
+    end
   end
 end

plugins/chat/lib/chat/user_notifications_extension.rb

@@ -73,7 +73,7 @@ module Chat
       # Prioritize messages from regular channels over direct messages
       if channels.any?
         channel_notification_text(
-          channels.sort_by { |channel| [channel.last_message_sent_at, channel.created_at] },
+          channels.sort_by { |channel| [channel.last_message.created_at, channel.created_at] },
           dm_users,
         )
       else