title: Get children count in linq to entities query
body: <p>I have a many to many relation between two tables in my database (MySql) :</p>
  
  <ul>
  <li>Category (id, name, id_parent)</li>
  <li>Sound (id, name)</li>
  </ul>
  
  <p>A category <strong><em>can</em></strong> have 1 parent category, so a category <strong><em>can</em></strong> have many children. If a category has at least one child, it has no sounds in it. I do not allow sounds and children categories together.</p>
  
  <p>So for a parent category, i want to get all children that may have children that may have children (...) and i want to count sounds in all children recursively.</p>
  
  <p>Exemple :</p>
  
  <p>Cat -> (CCat1 -> CCCat11(2 sounds), CCat2 (5 sounds), CCat3 -> CCat31 -> CCCat311 -> (CCCCat3111 (10 sounds), CCCCat3111 (1 sound))</p>
  
  <p>There is no deep limit, that's why i need a "recursively" way to count sounds.</p>
  
  <ul>
  <li>Cat has 3 children.</li>
  <li>CCat1 has 1 child.</li>
  <li>CCat2 has no child.</li>
  <li>CCat3 has 1 child that has 1 child that has 2 children.</li>
  </ul>
  
  <p>Cat.nbSounds = 18</p>