public function findParentRow($parentTable, $ruleKey = null, Zend_Db_Table_Select $select = null)
    {
        $db = $this->_getTable()->getAdapter();

        if (is_string($parentTable)) {
            $parentTable = $this->_getTableFromString($parentTable);
        }

        if (!$parentTable instanceof Zend_Db_Table_Abstract) {
            $type = gettype($parentTable);
            if ($type == 'object') {
                $type = get_class($parentTable);
            }
            throw new Zend_Db_Table_Row_Exception("Parent table must be a Zend_Db_Table_Abstract, but it is $type");
        }

        // even if we are interacting between a table defined in a class and a
        // table via extension, ensure to persist the definition
        if (($tableDefinition = $this->_table->getDefinition()) !== null
            && ($parentTable->getDefinition() == null)
        ) {
            $parentTable->setOptions(array(Zend_Db_Table_Abstract::DEFINITION => $tableDefinition));
        }

        if ($select === null) {
            $select = $parentTable->select();
        } else {
            $select->setTable($parentTable);
        }

        $map = $this->_prepareReference($this->_getTable(), $parentTable, $ruleKey);

        // iterate the map, creating the proper wheres
        for ($i = 0; $i < count($map[Zend_Db_Table_Abstract::COLUMNS]); ++$i) {
            $dependentColumnName = $db->foldCase($map[Zend_Db_Table_Abstract::COLUMNS][$i]);
            $value = $this->_data[$dependentColumnName];
            // Use adapter from parent table to ensure correct query construction
            $parentDb = $parentTable->getAdapter();
            $parentColumnName = $parentDb->foldCase($map[Zend_Db_Table_Abstract::REF_COLUMNS][$i]);
            $parentColumn = $parentDb->quoteIdentifier($parentTable->getName()) . '.';
            $parentColumn .= $parentDb->quoteIdentifier($parentColumnName, true);
            $parentInfo = $parentTable->info();

            // determine where part
            $type     = $parentInfo[Zend_Db_Table_Abstract::METADATA][$parentColumnName]['DATA_TYPE'];
            $nullable = $parentInfo[Zend_Db_Table_Abstract::METADATA][$parentColumnName]['NULLABLE'];
            if ($value === null && $nullable == true) {
                $select->where("$parentColumn IS NULL");
            } elseif ($value === null && $nullable == false) {
                return null;
            } else {
                $select->where("$parentColumn = ?", $value, $type);
            }

        }

        return $parentTable->fetchRow($select);
    }