Solr 4.0 specific query

Have Solr document:

<doc>
  <field name="name">El Chikilin De MaZaTlAn Sin</field>
  <field name="imageUrl">http://a4.l3-images.myspacecdn.com/images02/113/d4b1567ba13b46309335f9160dc56206/m.jpg</field>
  <field name="Sex">M</field>
  <field name="Age">25</field>
  <field name="Location">Norwalk, CA 90650, USA</field>
  <field name="Country">United States</field>
  <field name="LatLng">33.9077751,-118.0830047</field>
  <field name="longId">7640305676350546900</field>
  <field name="id">http://www.myspace.com/elzamarripa/classic</field>
  <field name="Books">el camasutra</field>
</doc>

It contains 10 fields. I'd like to select ALL DOCUMENTS that has fewer th开发者_运维百科en 10 fields in it. Is that possible?

Add a field to the schema that will represent the number of other fields. At index-time populate this field with the corresponding value (counting other fields). Then query this new field.