title: Compare two object lists with LINQ on specific property
body: <p>I have these two lists (where the <em>Value</em> in a <em>SelectListItem</em> is a bookingid):</p>
  
  <pre><code>List&lt;SelectListItem&gt; selectedbookings;
  List&lt;Booking&gt; availableBookings;
  </code></pre>
  
  <p>I need to find the ids from <code>selectedBookings</code> that are not in <code>availableBookings</code>. The LINQ join below will only get me the bookingids that are in <code>availableBookings</code>, and I'm not sure how to do it the other way around.</p>
  
  <p><code>!=</code> won't work since I'm comparing strings.</p>
  
  <pre><code>results = (
    from s in selectedbookings
    join a in availableBookings on s.bookingID.ToString() equals a.Value
    select s);
  </code></pre>