title: Django: loop over query and return newest related object
body: <p>I have <code>Unit</code> in my app that creating <code>Order</code>s and <code>Report</code>s each week, I want view that results as table containing name of <code>Unit</code>s in first column and 3 newest <code>Order</code>s and <code>Report</code>s in next 6 column. so i need query of Units and 3 of related Order and Report to each Unit.
  I try to use <code>prefetch_related</code> in this way but don't know how to limit it (and even make it work)</p>
  
  <pre><code>Unit.objects.filter(parent__name__contains="x").prefetch_related('order_set', 'reportfrom_set').order_by('order__date','reportfrom__submit_datetime')
  </code></pre>
  
  <p>Thanks in advance</p>