我是聚合框架的新手，有以下问题。
我的收藏是这样的：
用户
_id: ObjectId('604caef28aa89e769585f0c4')
baseData: {
firstName: "max"
username: "max_muster"
...
...
}
ActivitiesFeed
_id: ObjectId('604cb97c99bbd77b54047370')
userID: "604caef28aa89e769585f0c4" // the user id
activity: "604caf718aa89e769585f0c8" // the activity id
viewed: false
活动
_id: ObjectId('604caf718aa89e769585f0c8')
"baseData": {
"userID":"604caef28aa89e769585f0c4",
"type":0,
"title":"Alessandro send you a friend request.",
"description":"",
"actionID":"604caef28aa89e769585f0c4"
},
聚合函数
const response = ActivityFeed.aggregate([
{
$match: { userID: ObjectId(args.user) },
},
{
$lookup: {
from: 'activities',
localField: 'activity',
foreignField: '_id',
as: 'lookup_activities',
},
},
{ $unwind: '$activities' },
{
$lookup: {
from: 'users',
localField: 'lookup_activities.baseData.actionID',
foreignField: '_id',
as: 'lookup_users',
},
},
]);
如何使用第一个查找结果进行查找？
我查阅了activities集合。此集合保存第二个查找BaseData.UserID的id。但是使用这种方法，第二次查找没有结果。
我对activities集合进行连接的原因是actionID可以保存来自另一个集合的用户id或文档id。它取决于activities集合中的类型。
在聚合框架中是否可以进行依赖于前一个查找的类型和查找的查找？
提前谢谢你。
我所做的就是修复你的聚合体。您解出了错误的字段，请确保您的所有ID字段都是Objectid。如果您刚接触聚合功能，我强烈建议您使用MongoDB Compass来帮助您的聚合。他们有一个阶段一个阶段的辅助图形界面，这将真正使您的生活更容易。
蒙古游乐场
db.activitiesFeed.aggregate([
{
$match: {
userID: ObjectId("604caef28aa89e769585f0c4")
},
},
{
$lookup: {
from: "activities",
localField: "activity",
foreignField: "_id",
as: "lookup_activities",
},
},
{
$unwind: "$lookup_activities"
},
{
$lookup: {
from: "users",
localField: "lookup_activities.baseData.actionID",
foreignField: "_id",
as: "lookup_users",
},
},
])
使用的示例
db={
"users": [
{
_id: ObjectId("604caef28aa89e769585f0c4"),
baseData: {
firstName: "max",
username: "max_muster"
}
}
],
"activitiesFeed": [
{
_id: ObjectId("604cb97c99bbd77b54047370"),
userID: ObjectId("604caef28aa89e769585f0c4"),
activity: ObjectId("604caf718aa89e769585f0c8"),
viewed: false
}
],
"activities": [
{
_id: ObjectId("604caf718aa89e769585f0c8"),
"baseData": {
"userID": ObjectId("604caef28aa89e769585f0c4"),
"type": 0,
"title": "Alessandro send you a friend request.",
"description": "",
"actionID": ObjectId("604caef28aa89e769585f0c4")
},
}
]
}
