title: Mongoid not in query
body: <p>I have some trouble with mongoid:</p>
  
  <pre><code>  test "Test candidate" do
      User.create(:id =&gt; 1, :sex =&gt; User::Male, :country =&gt; 1, :city =&gt; 1)
      User.create(:id =&gt; 2, :sex =&gt; User::Female, :country =&gt; 1, :city =&gt; 1)
      User.create(:id =&gt; 3, :sex =&gt; User::Female, :country =&gt; 1, :city =&gt; 1)
  
      user = User.not_in(:id =&gt; [2]).second
      assert_not_equal(user.id, 2)
    end
  </code></pre>
  
  <p>Test failed. I've tried to use where(:id => {'$nid' => [2]}), but it have same effect.</p>
  
  <p>What is wrong? How to use "not in" condition with mongoid?</p>
  
  <p>PS, "second" is ok, with "first" test passed, because id=1</p>