/**
  * @param AW_Followupemail_Model_Rule|integer $rule
  *
  * @return AW_Followupemail_Model_Mysql4_Unsubscribe_Collection
  */
 public function addRuleFilter($rule)
 {
     if ($rule instanceof AW_Followupemail_Model_Rule) {
         $ruleId = $rule->getId();
     } elseif (is_numeric($rule)) {
         $ruleId = $rule;
     } else {
         return $this;
     }
     $this->addFieldToFilter('rule_id', $ruleId);
     return $this;
 }