Sometimes a set of circumstances will arise when the programmer is not certain what objects are available to a particular point of a symfony app (the manual is, at the time of writing, not entirely exhaustive).

Simply pop this code in your code temporarily and the output should give you some clues.

$vars = get_defined_vars();
foreach($vars as $key => $val) {
  $t = gettype($$key);
  echo "${key} (${t})<br />";
}