title: query.filter and gql
body: <p>I am trying this function, however something is wrong. I stored the name "John" but when i pass the john to <code>username_</code> and call the <code>check_user</code> the output is always <code>return results</code>, even if the name is not stored in google data store. Why?</p>
  
  <pre><code>def check_user(self, username_):
      query = db.Query(Registrations)
      results = query.filter('username =', username_)
      if results:
          return results
  
  user_username = self.request.get('username')
  check_username_valid = self.check_user(user_username)
  
   if not check_username_valid:
      error_username_exists="Username already exists"
  </code></pre>
  
  <p>In the case of GQL, how can i pass the variable <code>username_</code> into the query? like:</p>
  
  <pre><code> qr = db.GqlQuery("Select * from Registrations Where username = ?????")
  </code></pre>