class AvatarLookup def initialize(user_ids=[]) @user_ids = user_ids.tap(&:compact!).tap(&:uniq!).tap(&:flatten!) end # Lookup a user by id def [](user_id) users[user_id] end private def self.lookup_columns @lookup_columns ||= %i{id user_emails.email username uploaded_avatar_id} end def users @users ||= user_lookup_hash end def user_lookup_hash # adding tap here is a personal taste thing hash = {} User.joins(:user_emails) .where(id: @user_ids) .select(AvatarLookup.lookup_columns) .each{ |user| hash[user.id] = user } hash end end