title: AD PrincipalSearcher: Search where property does not contain some value
body: <p>Principal Searcher seems to do a great job when building a filter to find an object with a particular value.  What about without?  For example How do I build a filter to exclude everyone with "Joe" in their name. The code below would not work. </p>
  
  <pre><code>        PrincipalContext ctx = new PrincipalContext(ContextType.Domain);
          UserPrincipal qbeUser = new UserPrincipal(ctx);
          PrincipalSearcher srch = new PrincipalSearcher(qbeUser);
  
           //this is the problem line.  How to format to exclude values with Joe?
           qbeUser.Name != "*Joe*"; 
  
          srch.QueryFilter = qbeUser;
          foreach (var found in srch.FindAll())
           { do something to non Joe users... }
  </code></pre>
  
  <p>....</p>