将日期格式更改为数组中的yyyy / mm / dd并转换为json格式

Here's my controller code:

这是我的控制器代码：

$news = Model::factory('News')->get_all_news($user_id);   
$news->as_array();

foreach($news as $news):
    $sa[] = $news->as_array();
endforeach;

echo '{"news":'.json_encode($sa).'}';
$news