How to join three (multipe) collections with $lookup in mongodb?
Hi I am looking to join data from three collection
users collection:
[
{
_id:0,
name:"abc",
phone:999999999
},
{
_id:1,
name:"xyz",
phone:888888888
},
]
product collection:
[
{
_id:"p01",
name:"product-name",
price:1200
},
{
_id:"p02",
name:"product-name1",
price:100
}
]
productreviews collection:
[
{
_id:"pr0",
userId:0,
productId:"p01",
star:4
},
{
_id:"pr1",
userId:1,
productId:"p01",
star:3
}
]
mongodb query:
product.aggregate([
{
$lookup: {
from: "productreviews",
localField: "_id",
foreignField: "productId",
as: "review",
},
},
{
$lookup: {
from: "users",
localField: "review.userId",
foreignField: "_id",
as: "review.userInfo",
},
},
])
I am not able to get that output which i need. How can i get this following output:
{
product: [
{
_id: "p01",
name: "product-name",
price: 1200,
review: [
{
_id: "pr0",
userId: 0,
productId: "p01",
star: 4,
"userInfo": {
name: "abc",
phone: 999999999
}
},
{
_id: "pr1",
userId: 1,
productId: "p01",
star: 3,
"userInfo": {
"name": "xyz",
"phone": 888888888,
}
},
]
},
{
_id: "p02",
name: "product-name1",
price: 100,
},
]
}
Any help appreciated!. Thank You...
db.product.aggregate([
{
$lookup: {
from: "review",
localField: "_id",
foreignField: "productId",
as: "review",
},
},
{
$lookup: {
from: "users",
localField: "review.userId", //See here
foreignField: "_id",
as: "review.userInfo",
},
},
])
Local field name is userId in the second lookup.
EDIT:
Add a unwind stage
db.product.aggregate([
{
$lookup: {
from: "review",
localField: "_id",
foreignField: "productId",
as: "review",
},
},
{
"$unwind": "$review"
},
{
$lookup: {
from: "users",
localField: "review.userId",
foreignField: "_id",
as: "review.userInfo",
},
},
])
To keep the docs where there is no match, preserve null arrays at unwind stage as below
{
$unwind: {
path: "$review",
"preserveNullAndEmptyArrays": true
}
}