(PECL mongo >=0.9.0)
MongoCollection::createDBRef — 创建一个数据库引用
document_or_id
If an array or object is given, its _id field will be used as the reference ID. If a MongoId or scalar is given, it will be used as the reference ID.
返回一个数据库的引用数组。
如果提供了不包含 _id 字段的数组当做 document_or_id 参数，将会返回 NULL。
Example #1 MongoCollection::createDBRef() 例子
<?php
$songs = $db->songs;
$playlists = $db->playlists;
// 为 song 创建引用
$manamana = $songs->findOne(array('title' => 'Ma na ma na'));
$refToSong = $songs->createDBRef($manamana);
// 添加引用到我的播放列表
$playlists->update(array('username' => 'me'), array('$push' => array('songlist' => $refToSong)));
?>