title: Linq join with COUNT
body: <p>I have 2 tables, Forums and Posts.<br>
  I want to retrieve all Forums fields with a new extra field: count all post that belong to this forum.</p>
  
  <p>I have this for now:</p>
  
  <pre><code>var v =(from forum in Forums
      join post in Posts on forum.ForumID equals post.Forum.ForumID 
      select new 
      {
          forum, //Need to retrieve all fields/columns from forum     
          PostCount = //count all post that belong to this forum with a condition: count it only if post.Showit==1
  
      }
      ).Distinct()
  </code></pre>
  
  <ol>
  <li>The join must be Left join: if there are no post that belongs to some forum, the forums fields should be retrieved but PostCount field should be 0.  </li>
  <li>The result set must be distinct (join gives me the full cross...or how it's called)</li>
  </ol>