title: add a field value from code
body: <p>I'm using Grocery CRUD with CodeIgniter, and I have this table :</p>
  
  <pre><code>annonce (id, name, id_user).
  </code></pre>
  
  <p>the <code>id_user</code> is a foreign key which references to another table <code>user(id,....).</code></p>
  
  <p>I don't want to add the <code>user_id</code> in an input when I add an entry in the annonce table, I have the <code>user_id</code> in the session, so I want when I add a new entry to specify the user id in the code.</p>
  
  <p>how can I do that ?</p>