如何追加 stdClass 对象

我有一个像joomla这样的stdClass对象，就像这样

$db->setQuery($sql);
$schoollist = $db->loadObjectList(); 

$schoollist变量包含以下 stdClass 对象

stdClass Object ( [id] => 1 [col1] => blabla [col2] => 5 [col3] => 208 ) 
stdClass Object ( [id] => 2 [col1] => test1 [col2] => 1 [col3] => 52 ) 

我需要在查询后添加另一个“列”，如[col4] = > dsdads，所以结果会像这样

stdClass Object ( [id] => 1 [col1] => blabla [col2] => 5 [col3] => 208 [col4] => 208) 
stdClass Object ( [id] => 2 [col1] => test1 [col2] => 1 [col3] => 52 [col4] => 208) 

我该怎么做？