Populating all items from ref model [duplicate] - node.js

Question

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$lookup multiple levels without $unwind?
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Mongoose: deep population (populate a populated field)
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Closed 3 years ago.
I have a database structured like this:
I want to get all listItems, of all lists from a user with a x ID. What's the correct way of doing that?
I'm using node with mongoose, and I tried the following:
await User.findById(user._id).populate('list');
But realized that I can't populate all ListItem's from that. Meaning, I can't do this:
await User.findById(user._id).populate('list').populate('listItem');
How can I get all listItems, of all lists from a user with a x ID?

Answer 1

Assuming User, List, and ListItem are Collections, you should be able to accomplish this using $lookup..
Here is a live demo of the following query..
Query:
db.users.aggregate([
{
$match: {
uniqueId: 1
}
},
{
$lookup: {
from: "lists",
localField: "uniqueId",
foreignField: "userId",
as: "lists"
}
},
{
$lookup: {
from: "listItems",
localField: "uniqueId",
foreignField: "userId",
as: "listItems"
}
}
])
Dataset:
db={ // Simulates a DB ********
"users": [ // Simulates a Collection ********
{
"firstname": "John",
"lastname": "Smith",
"email": "jsmith#gmail.com",
"password": "password123",
"uniqueId": 1
},
{
"firstname": "Jane",
"lastname": "Doe",
"email": "doe#yahoo.com",
"password": "123password",
"uniqueId": 2
}
],
"lists": [ // Simulates a Collection ********
{
"userId": 1,
"name": "Johns List 1",
"items": [
11,
12,
13
]
},
{
"userId": 2,
"name": "Groceries",
"items": [
21,
22,
23
]
}
],
"listItems": [ // Simulates a Collection ********
{
"userId": 2,
"itemId": 21,
"title": "Apple",
"notes": []
},
{
"userId": 2,
"itemId": 22,
"title": "Banana",
"notes": []
},
{
"userId": 2,
"itemId": 23,
"title": "Strawberry",
"notes": []
},
{
"userId": 1,
"itemId": 11,
"title": "Oil Change",
"notes": []
},
{
"userId": 1,
"itemId": 12,
"title": "Pick Up Grandma",
"notes": []
},
{
"userId": 1,
"itemId": 13,
"title": "Go For Run",
"notes": []
}
]
}
Result:
[
{
"_id": ObjectId("5a934e000102030405000008"),
"email": "jsmith#gmail.com",
"firstname": "John",
"lastname": "Smith",
"listItems": [
{
"_id": ObjectId("5a934e000102030405000003"),
"itemId": 11,
"notes": [],
"title": "Oil Change",
"userId": 1
},
{
"_id": ObjectId("5a934e000102030405000004"),
"itemId": 12,
"notes": [],
"title": "Pick Up Grandma",
"userId": 1
},
{
"_id": ObjectId("5a934e000102030405000005"),
"itemId": 13,
"notes": [],
"title": "Go For Run",
"userId": 1
}
],
"lists": [
{
"_id": ObjectId("5a934e000102030405000006"),
"items": [
11,
12,
13
],
"name": "Johns List 1",
"userId": 1
}
],
"password": "password123",
"uniqueId": 1
}
]