title: can't catch exception in codeIgniter
body: <p>Sorry for my english but please i need help 
  i have a problem when i'm trying to catch an insert query </p>
  
  <p>i have a table Employe with 3 primary keys (Matricule , CIN , name)</p>
  
  <p>i want to catch the exception when i add a new employe with duplicated values</p>
  
  <p>My Model </p>
  
  <pre><code>  function insert_Employe($donnees){
     try{
      $this-&gt;db-&gt;insert('Employe',$donnees);
      return 'employe enregistré avec succes';
     }catch(Exception $e)
     {
         return $e-&gt;getMessage();
     }
  }
  </code></pre>
  
  <p>My controller</p>
  
  <pre><code>  function nouveau(){
      if(!$this-&gt;offres-&gt;_isLogged() || !$this-&gt;input-&gt;post('Ajax')==1){
          redirect(base_url().'users');
      }
      $values = $this-&gt;_get_values();
      try{
      $message = $this-&gt;employe-&gt;insert_Employe($values);
      echo $message;
      }catch(Exception $e){
          echo $e-&gt;getMessage();
      }
  }
  </code></pre>
  
  <p>i can't catch the exception </p>