Filter documents that have id in another collection in MongoDB with aggregation framework - mongodb

Question

So I have two collection. collectionA and collectionB
collection A has following documents
db={
"collectiona": [
{
"_id": "6173ddf33ed09368a094e68a",
"title": "a"
},
{
"_id": "61wefdf33ed09368a094e6dc",
"title": "b"
},
{
"_id": "61wefdfewf09368a094ezzz",
"title": "c"
},
],
"collectionb": [
{
"_id": "6173ddf33ed0wef368a094zq",
"collectionaID": "6173ddf33ed09368a094e68a",
"data": [
{
"userID": "123",
"visibility": false,
"response": false
},
{
"userID": "2345",
"visibility": true,
"response": true
}
]
},
{
"_id": "6173ddf33ed09368awef4e68g",
"collectionaID": "61wefdf33ed09368a094e6dc",
"data": [
{
"userID": "5678",
"visibility": false,
"response": false
},
{
"userID": "674",
"visibility": true,
"response": false
}
]
}
]
}
So What I need is documents from collection A which has response false in collection B
and document should be sorted by first the ones that have visibility false and then the ones that have visibility true
for eg. userID : 123 should get 3 documents
{
"_id": "6173ddf33ed09368a094e68a",
"title": "a"
},
{
"_id": "61wefdf33ed09368a094e6dc",
"title": "b"
},
{
"_id": "61wefdfewf09368a094ezzz",
"title": "c"
},
whereas userID 2345 should get two
{
"_id": "61wefdf33ed09368a094e6dc",
"title": "b"
},
{
"_id": "61wefdfewf09368a094ezzz",
"title": "c"
},
User 674 will receive 3 objects from collection A but second would be in the last as it has visibility true for that document
{
"_id": "6173ddf33ed09368a094e68a",
"title": "a"
},
{
"_id": "61wefdfewf09368a094ezzz",
"title": "c"
},
{
"_id": "61wefdf33ed09368a094e6dc",
"title": "b"
},
MongoDB Playground link : https://mongoplayground.net/p/3rLry0FPlw-
Really appreciate the help. Thanks

Answer 1

You can start from collectionA:
$lookup the collectionB for the record related to the user specified
filter out collectionB documents according to response
assign a helper sortrank field based on the visibility and whether collectionaID is a match
$sort according to sortrank
wrangle back to the raw collection A
db.collectiona.aggregate([
{
"$lookup": {
"from": "collectionb",
let: {
aid: "$_id"
},
"pipeline": [
{
$unwind: "$data"
},
{
$match: {
$expr: {
$and: [
{
$eq: [
"$data.userID",
"2345"
]
},
{
$eq: [
"$collectionaID",
"$$aid"
]
}
]
}
}
}
],
"as": "collB"
}
},
{
$match: {
"collB.data.response": {
$ne: true
}
}
},
{
"$unwind": {
path: "$collB",
preserveNullAndEmptyArrays: true
}
},
{
"$addFields": {
"sortrank": {
"$cond": {
"if": {
$eq: [
"$collB.data.visibility",
false
]
},
"then": 1,
"else": {
"$cond": {
"if": {
$eq: [
"$collB.collectionaID",
"$_id"
]
},
"then": 3,
"else": 2
}
}
}
}
}
},
{
$sort: {
sortrank: 1
}
},
{
$project: {
collB: false,
sortrank: false
}
}
])
Here is the Mongo playground for your reference.