mysql_real_escape_string() error when loading query in model

[eluser]SouthOfZeeland[/eluser]
I have a strange problem. Consider this model and controller. (note: I autoload the database library).

Code:

class TestModel extends Model {

  private $created_on;

  function __construct() {
    parent::Model();
    $this->created_on = time();
  }

  function dbTest($value) {
    $sql = "select * from sometable where name = ?";
    $query = $this->db->query($sql, $value);
    return $query->num_rows();
  }

}

Code:

class TestController extends Controller {

  function TestController() {
    $this->load->model('TestModel');
    $testvar = new TestModel;
    echo $testvar->dbTest('John');
  }

}

It should output 0, but instead I get this error:

Code:

A PHP Error was encountered

Severity: Warning

Message: mysql_real_escape_string() expects parameter 2 to be resource, integer given

Filename: mysql/mysql_driver.php

Line Number: 227

When I use this code in my model:

Code:

function dbTest($value) {
  $sql = "select * from sometable where name = '$value'";
  $query = $this->db->query($sql);
  return $query->num_rows();
}

...it works just fine. So the problem lies within the query bindings.

Any ideas?

TIA