title: does not contain a definition for 'Sum'
body: <p>I have <code>using System.Linq;</code> so I am thinking my syntax has to be wrong but I can't see it</p>
  
  <pre><code>public void Count()
  {
      var count = _context.Objects
          .Select(i =&gt; new { i, ViewCount = i.Relations.Sum(j =&gt; j.ViewCount) });
  }
  </code></pre>