title: SQLAlchemy conversion of Django annotate
body: <p>I have the following annotation in a Django model manager I'd like to convert to a SQLAlchemy ORM query:</p>
  
  <pre><code>annotations = {
          'review_count' : Count("cookbookreview", distinct=True), 
          'rating' : Avg("cookbookreview__rating")
      }
  return self.model.objects.annotate(**annotations)
  </code></pre>
  
  <p>What I essentially need is each model object in the query to have <code>review_count</code> and <code>rating</code> attached to them as part of the initial query. I believe I can use <code>column_property</code>, but I would like to avoid this type of "calculated property" on the object, because I don't want the property (expensive lookup) being done for each object when I access the property in a template.</p>
  
  <p>What is the right way to approach this problem? Thanks in advance.</p>