Example for https://stackoverflow.com/questions/64703305/rails-5-activerecord-optional-inclusive-where-for-nested-associations-attribute

so-64703305.html.erb

<ul>
  <% @users.each do |user| %>
    <li>
      <%= user.name %>
      <% if (orders = user.orders_in_timespan(@start_date, @end_date)).any? %>
        <ul>
          <% orders.each do |order| %>
            <li><%= order.number %></li>
          <% end %>
        </ul>
      <% end %>
    </li>
  <% end %>
</ul>