Fix multiple N+1s in ConversationsController (mastodon#25134)

app/controllers/api/v1/conversations_controller.rb

@@ -11,7 +11,7 @@ class Api::V1::ConversationsController < Api::BaseController
 
   def index
     @conversations = paginated_conversations
-    render json: @conversations, each_serializer: REST::ConversationSerializer
+    render json: @conversations, each_serializer: REST::ConversationSerializer, relationships: StatusRelationshipsPresenter.new(@conversations.map(&:last_status), current_user&.account_id)
   end
 
   def read
@@ -32,7 +32,20 @@ def set_conversation
 
   def paginated_conversations
     AccountConversation.where(account: current_account)
-                       .to_a_paginated_by_id(limit_param(LIMIT), params_slice(:max_id, :since_id, :min_id))
+                       .includes(
+                         account: :account_stat,
+                         last_status: [
+                           :media_attachments,
+                           :preview_cards,
+                           :status_stat,
+                           :tags,
+                           {
+                             active_mentions: [account: :account_stat],
+                             account: :account_stat,
+                           },
+                         ]
+                       )
+                       .to_a_paginated_by_id(limit_param(LIMIT), **params_slice(:max_id, :since_id, :min_id))
   end
 
   def insert_pagination_headers

app/models/account_conversation.rb

@@ -17,6 +17,8 @@
 class AccountConversation < ApplicationRecord
   include Redisable
 
+  attr_writer :participant_accounts
+
   before_validation :set_last_status
   after_commit :push_to_streaming_api
 
@@ -26,24 +28,40 @@ class AccountConversation < ApplicationRecord
 
   def participant_account_ids=(arr)
     self[:participant_account_ids] = arr.sort
+    @participant_accounts = nil
   end
 
   def participant_accounts
-    if participant_account_ids.empty?
-      [account]
-    else
-      participants = Account.where(id: participant_account_ids)
-      participants.empty? ? [account] : participants
+    @participant_accounts ||= begin
+      if participant_account_ids.empty?
+        [account]
+      else
+        participants = Account.where(id: participant_account_ids).to_a
+        participants.empty? ? [account] : participants
+      end
     end
   end
 
   class << self
-    def to_a_paginated_by_id(limit, options = {})
-      if options[:min_id]
-        paginate_by_min_id(limit, options[:min_id], options[:max_id]).reverse
-      else
-        paginate_by_max_id(limit, options[:max_id], options[:since_id]).to_a
+    def to_a_paginated_by_id(limit, min_id: nil, max_id: nil, since_id: nil, preload_participants: true)
+      array = begin
+        if min_id
+          paginate_by_min_id(limit, min_id, max_id).reverse
+        else
+          paginate_by_max_id(limit, max_id, since_id).to_a
+        end
       end
+
+      if preload_participants
+        participant_ids = array.flat_map(&:participant_account_ids)
+        accounts_by_id = Account.where(id: participant_ids).index_by(&:id)
+
+        array.each do |conversation|
+          conversation.participant_accounts = conversation.participant_account_ids.filter_map { |id| accounts_by_id[id] }
+        end
+      end
+
+      array
     end
 
     def paginate_by_min_id(limit, min_id = nil, max_id = nil)