title: MongoDB sort order - mix of ascending and descending fields
body: <p>I want to sort a MongoDB collection based upon several fields, some ascending, other descending.
  I'm using the official C# driver. My code currently looks like this:</p>
  
  <pre><code>string[] sortFields = new[] { "surname", "firstname","companyname","email" }; 
  MongoDB.Driver.Builders.SortByBuilder sort = MongoDB.Driver.Builders.SortBy.Ascending(sortFields);
  foreach (MongoDB.Bson.BsonDocument doc in contactsCollection.FindAs&lt;MongoDB.Bson.BsonDocument&gt;(query).SetSortOrder(sort))
  {
  ...
  </code></pre>
  
  <p>How do I alter this code so it sorts on descending for email?</p>
  
  <p>Thanks very much.</p>