擅长:python、mysql、java
<p>您可以使用<code>$project</code>代替<code>$group</code>:</p>
<pre><code>db.users.aggregate([
{
"$lookup": {
"from": "events",
"localField": "event",
"foreignField": "_id",
"as": "Events"
}
},
{
"$unwind": "$Events"
},
{
$project: {
_id: 1,
name: 1,
event: "$Events.name"
}
}
])
</code></pre>