title: Django: Return array in subquery
body: <p>I have a model <code>Application</code> that has many <code>Judge</code> objects assigned to it via ForeignKey. Each <code>Judge</code> will grade the <code>Application</code>. I want to return a list of Applications in a QuerySet along with an array of each of the score values. Here's how I"m trying to accomplish that:</p>
  
  <pre><code>total_scores = Subquery(
      Judge.objects
      .filter(
          application=OuterRef('pk')
      )
      .values_list(
          'total_score',
          flat=True
      )
  )
  
  applications = Application.objects \
      .annotate(
          score_array=total_scores
      )
  </code></pre>
  
  <p>But I get this error:</p>
  
  <blockquote>
    <p>more than one row returned by a subquery used as an expression</p>
  </blockquote>
  
  <p>The <code>values_list</code> should return an array of values, so i'm not sure why multiple rows are being returned from my subquery. Any pointers? Thanks.</p>