group member count optimization

app/models/group.rb

@@ -15,6 +15,7 @@
 #  is_archived              :boolean          default(FALSE), not null
 #  created_at               :datetime         not null
 #  updated_at               :datetime         not null
+#  member_count             :integer          default(0)
 #
 
 class Group < ApplicationRecord

app/models/group_account.rb

@@ -21,10 +21,20 @@ class GroupAccount < ApplicationRecord
   validates :account_id, uniqueness: { scope: :group_id }
 
   after_commit :remove_relationship_cache
+  after_create :increment_member_count
+  after_destroy :decrement_member_count
 
   private
 
   def remove_relationship_cache
     Rails.cache.delete("relationship:#{account_id}:group#{group_id}")
   end
+
+  def increment_member_count
+    group&.increment!(:member_count)
+  end
+
+  def decrement_member_count
+    group&.decrement!(:member_count)
+  end
 end

app/serializers/rest/group_serializer.rb

@@ -22,8 +22,4 @@ class REST::GroupSerializer < ActiveModel::Serializer
 
     full_asset_url(object.cover_image.url)
   end
-
-  def member_count
-    object.accounts.count
-  end
 end