Only preload accounts in Collections when needed (#39143)

app/models/collection.rb

@@ -64,11 +64,15 @@ class Collection < ApplicationRecord
     !local?
   end
 
-  def items_for(account = nil)
-    result = collection_items.with_accounts
-    result = account == self.account ? result.pending_or_accepted : result.accepted
-    result = result.not_blocked_by(account) unless account.nil?
-    result
+  def items_for(account = nil, include_accounts: false)
+    @items_for ||= {}
+    @items_for[account] ||= begin
+      result = collection_items
+      result = result.with_accounts if include_accounts
+      result = account == self.account ? result.pending_or_accepted : result.accepted
+      result = result.not_blocked_by(account) unless account.nil?
+      result
+    end
   end
 
   def tag_name

app/models/collection_item.rb

@@ -43,7 +43,7 @@ class CollectionItem < ApplicationRecord
 
   scope :ordered, -> { order(position: :asc) }
   scope :with_accounts, -> { includes(account: [:account_stat, :user]) }
-  scope :not_blocked_by, ->(account) { where.not(accounts: { id: account.blocking }) }
+  scope :not_blocked_by, ->(account) { joins(:account).where.not(accounts: { id: account.blocking }) }
   scope :local, -> { joins(:collection).merge(Collection.local) }
   scope :accepted_partial, ->(account) { joins(:account).merge(Account.local).accepted.where(uri: nil, account_id: account.id) }
   scope :pending_or_accepted, -> { where(state: [:pending, :accepted]) }

app/serializers/rest/collection_with_accounts_serializer.rb

@@ -10,6 +10,6 @@ class REST::CollectionWithAccountsSerializer < ActiveModel::Serializer
   end
 
   def accounts
-    [object.account] + object.collection_items.filter_map(&:account)
+    [object.account] + object.items_for(current_user&.account, include_accounts: true).map(&:account)
   end
 end

spec/models/collection_spec.rb

@@ -124,6 +124,28 @@ RSpec.describe Collection do
         expect(subject.items_for(account)).to match_array(accepted_items + [pending_item])
       end
     end
+
+    context 'when `include_accounts` is set to `true`' do
+      it 'preloads accounts' do
+        items = subject.items_for(include_accounts: true).to_a
+
+        expect { items.first.account }.to_not execute_queries
+      end
+    end
+
+    context 'when called multiple times' do
+      let(:account) { subject.account }
+
+      it 'memoizes results' do
+        subject.items_for.to_a
+
+        expect { subject.items_for.to_a }.to_not execute_queries
+
+        expect { subject.items_for(account).to_a }.to execute_queries
+
+        expect { subject.items_for(account).to_a }.to_not execute_queries
+      end
+    end
   end
 
   describe '#tag_name=' do