如何在mongodb中提取对象ID并对其进行搜索?

请注意,我的 plans 集合不是对象id。我已将其存储在 集合引用用户在 user_accounts 收藏。我考虑过在所有集合中存储用户名以引用用户,但如果用户希望更改其用户名,那就不太可能了。

// Retrieve User ID
$query = array("username" => $user_id);
$fields = array("_id");
$user = $collection_user->findOne($query, $fields);

// Retrieve plans made by user
$query = array("user_id" => $user['_id']);
$fields = array("plan_title");
$data = $collection_plans->find($query, $fields);

// Retrieve plans made by user
$query = array("user_id" => "4cc1790f6c0d49bf9424fc73");
$fields = array("plan_title");
$data = $collection_plans->find($query, $fields);