title: group by month and year parts using queryover
body: <p>I have a model, that contains a DateTime field and a Price field.
  I want to get a list that gives me an aggregation of month/year - price
  so for the data:</p>
  
  <ol>
  <li>15/01/2012 200</li>
  <li>16/01/2012 200</li>
  <li>15/02/2012 300</li>
  <li>16/02/2012 300</li>
  <li>15/03/2012 400</li>
  <li>16/03/2012 400</li>
  </ol>
  
  <p>I will get:</p>
  
  <ol>
  <li>01/2012 400</li>
  <li>02/2012 600</li>
  <li>03/2012 800</li>
  </ol>
  
  <p>So far I didn't find a way to achive this using QueryOver.
  I keep getting "could not resolve property" when i try to look at the Month/Year parts of the date.</p>
  
  <p>Those questions:</p>
  
  <p><a href="https://stackoverflow.com/questions/6380844/group-posts-by-year-then-by-month">Group posts by year, then by month</a></p>
  
  <p><a href="https://stackoverflow.com/questions/8377563/group-sort-by-date-year-month-partial-select-with-nhibernate-projection-trans">Group/Sort by Date Year/Month, Partial Select with NHibernate (Projection? Transformation?)</a></p>
  
  <p>got answered using LINQ - not what I'm looking for.</p>
  
  <p>Any ideas?
  Thanks</p>
  
  <p>(using NHibernate 3.2)</p>