Working with Mongodb References inside array next to other content - arrays

Question

I want to use the mongodb aggregation framework on 3 Collections that have to "come together" to one Query. The problem is, when I'm referencing to another collection with $lookup it deletes the other content of the array the reference is in.
Heres the collection my aggregation starts in (users):
{
"_id" : ObjectId("5c9bea89f4fe8c37175ade58"),
"kundennummer" : "000001",
"passwort" : "xxx",
"status" : "1",
"onlinestatus" : true,
"kontakt" : {
"email" : "test#test.net"
},
"thing" : [
{
"thing_id" : 2,
"onlinestatus" : false,
"status" : true,
"site" : [
{
"site_id" : 3,
"status": true
},
{
"site_id" : 4,
"status": true
}
],
"refs" : [
{
"thing_id" : 11,
"status" : true
},
{
"thing_id" : 22,
"status" : true
}
]
}
]
}
when I know want site to be extended by the content given in site collection like this:
{
"_id": 11,
"name": "test"
},
{
"_id": 22,
"name": "test2"
}
I tried to use $lookup and the status: true disappeared.
db.users.aggregate([{
$lookup:
{
from: "sites",
localField: "things.site.site_id",
foreignField: "_id",
as: "things.site"
}
}])
edit:
What I want to achieve is the following:
{
"_id" : ObjectId("5c9bea89f4fe8c37175ade58"),
"kundennummer" : "000001",
"passwort" : "xxx",
"status" : "1",
"onlinestatus" : true,
"kontakt" : {
"email" : "test#test.net"
},
"thing" : [
{
"thing_id" : 2,
"onlinestatus" : false,
"status" : true,
"site" : [
{
"site_id" : 11,
"status": true,
"name": "test"
},
{
"site_id" : 12,
"status": true,
"name": "test2"
}
],
"refs" : [
{
"thing_id" : 11,
"status" : true,
"name": "test"
},
{
"thing_id" : 12,
"status" : true,
"name": "test2"
}
]
}
]
}

Answer 1

To use $lookup on the embedded document in MongoDB aggregation you need to use $unwind. It will output a document for each element and then you can use $lookup. You will get results from sites as well with the help of the below query:
db.user.aggregate([
{
$unwind: "$thing"
},
{
$unwind: "$thing.site"
},
{
$unwind: "$thing.refs"
},
{
$lookup: {
from: 'sites',
let: { 'siteId': '$thing.site.site_id' },
pipeline: [
{
$match: {
$expr: {
$eq: ['$_id', '$$siteId']
}
}
},
],
as: 'siteObject'
}
},
{
$lookup: {
from: 'things',
let: { 'thingId': '$thing.refs.thing_id' },
pipeline: [
{
$match: {
$expr: {
$eq: ['$_id', '$$thingId']
}
}
},
],
as: 'thingObject'
}
},
{
$unwind: "$siteObject"
},
{
$unwind: "$thingObject"
},
{
$project: {
"_id" : 1,
"kundennummer" : 1,
"passwort" : 1,
"status" : 1,
"onlinestatus" : 1,
"kontakt" : 1,
"thing": [{
"thing_id" : "$thing.thing_id",
"onlinestatus" : "$thing.onlinestatus",
"status" : "$thing.status",
"site" : {
"site_id":"$thing.site.site_id",
"status":"$thing.site.status",
"siteName":"$siteObject.siteName",
},
"refs" : {
"thing_id":"$thing.refs.thing_id",
"status":"$thing.refs.status",
"siteName":"$thingObject.thingName",
},
}]
}
},
{
$unwind: "$thing"
},
{
$group: {
_id: {
"_id": "$_id",
"kundennummer": "$kundennummer",
"passwort": "$passwort",
"status":"$status",
"onlinestatus":"$onlinestatus",
"kontakt":"$kontakt"
},
thing: { $push: { thing_id: "$thing.thing_id", onlinestatus: "$thing.onlinestatus", status: "$thing.status",site:"$thing.site",refs: "$thing.refs" } }
}
}
])
This will result as below:
{
"_id" : {
"_id" : ObjectId("5c9bea89f4fe8c37175ade58"),
"kundennummer" : "000001",
"passwort" : "xxx",
"status" : "1",
"onlinestatus" : true,
"kontakt" : {
"email" : "test#test.net"
}
},
"thing" : [
{
"thing_id" : 2,
"onlinestatus" : false,
"status" : true,
"site" : {
"site_id" : ObjectId("5caf395e512ab5123bb4b0af"),
"status" : true,
"siteName" : "Moto"
},
"refs" : {
"thing_id" : ObjectId("5cb042ea512ab5123bb4b0b0"),
"status" : true,
"siteName" : "hi"
}
},
{
"thing_id" : 2,
"onlinestatus" : false,
"status" : true,
"site" : {
"site_id" : ObjectId("5caf395e512ab5123bb4b0af"),
"status" : true,
"siteName" : "Moto"
},
"refs" : {
"thing_id" : ObjectId("5cb042ea512ab5123bb4b0b1"),
"status" : true,
"siteName" : "world"
}
},
{
"thing_id" : 2,
"onlinestatus" : false,
"status" : true,
"site" : {
"site_id" : ObjectId("5caf395e512ab5123bb4b0ae"),
"status" : true,
"siteName" : "hello"
},
"refs" : {
"thing_id" : ObjectId("5cb042ea512ab5123bb4b0b0"),
"status" : true,
"siteName" : "hi"
}
},
{
"thing_id" : 2,
"onlinestatus" : false,
"status" : true,
"site" : {
"site_id" : ObjectId("5caf395e512ab5123bb4b0ae"),
"status" : true,
"siteName" : "hello"
},
"refs" : {
"thing_id" : ObjectId("5cb042ea512ab5123bb4b0b1"),
"status" : true,
"siteName" : "world"
}
}
]
}
Result is near by your desired result and i think you should not follow such schema it will make your every query more complex.