Merge mongodb aggregation results of unread messages count per conversation member into document - mongodb

Question

I want to aggregate unread messages count per member in a conversation group and seems my aggregation pipeline is working correctly, but, I don't know how to achieve the following results.
Please check the example.
Thread documents
/* 1 */
{
"_id" : ObjectId("60d4efa6a95f446051f31492"),
"latestMessage" : "Voluptatem eos officiis optio dolor est et.",
"type" : "FEED",
"users" : [
{
"_id" : ObjectId("60d4efa6a95f446051f31491"),
"displayName" : "Monique Connelly II"
},
{
"_id" : ObjectId("60d4efa6a95f446051f31490"),
"displayName" : "Ivory Jacobson DDS"
},
{
"_id" : ObjectId("60d4efa6a95f446051f3148f"),
"displayName" : "Ron Weimann"
}
],
"createdBy" : "60d4efa6a95f446051f3148f",
"createdAt" : ISODate("2021-06-24T20:48:38.537Z"),
"modifiedAt" : ISODate("2021-06-24T20:48:38.620Z"),
}
/* 2 */
{
"_id" : ObjectId("60d4efa6a95f446051f31493"),
"type" : "CONVERSATION",
"users" : [
{
"_id" : ObjectId("60d4efa6a95f446051f31491"),
"displayName" : "Monique Connelly II"
},
{
"_id" : ObjectId("60d4efa6a95f446051f31490"),
"displayName" : "Ivory Jacobson DDS"
},
{
"_id" : ObjectId("60d4efa6a95f446051f3148f"),
"displayName" : "Ron Weimann"
}
],
"createdBy" : "60d4efa6a95f446051f3148f",
"createdAt" : ISODate("2021-06-24T20:48:38.569Z"),
"modifiedAt" : ISODate("2021-06-24T20:48:38.569Z"),
}
Message documents
/* 1 */
{
"_id" : ObjectId("60d4efa6a95f446051f31494"),
"content" : "Itaque rerum facere neque fuga aspernatur dolorum.",
"deleted" : false,
"threadId" : ObjectId("60d4efa6a95f446051f31492"),
"type" : "TEXT",
"thread" : {
"$ref" : "threads",
"$id" : ObjectId("60d4efa6a95f446051f31492")
},
"readBy" : [
ObjectId("60d4efa6a95f446051f3148f")
],
"attributes" : [],
"createdBy" : "60d4efa6a95f446051f3148f",
"createdAt" : ISODate("2021-06-24T20:48:38.598Z"),
"modifiedAt" : ISODate("2021-06-24T20:48:38.598Z"),
}
/* 2 */
{
"_id" : ObjectId("60d4efa6a95f446051f31495"),
"content" : "Nisi suscipit iste magni voluptatem.",
"deleted" : false,
"threadId" : ObjectId("60d4efa6a95f446051f31492"),
"type" : "TEXT",
"thread" : {
"$ref" : "threads",
"$id" : ObjectId("60d4efa6a95f446051f31492")
},
"readBy" : [
ObjectId("60d4efa6a95f446051f3148f")
],
"attributes" : [],
"createdBy" : "60d4efa6a95f446051f3148f",
"createdAt" : ISODate("2021-06-24T20:48:38.610Z"),
"modifiedAt" : ISODate("2021-06-24T20:48:38.610Z"),
}
and more...
My aggregation pipeline
db.threads.aggregate([
{ "$lookup": { "from": "messages", "localField": "_id", "foreignField": "threadId", "as": "message"}},
{ "$unwind": "$message" },
{ "$unwind": "$users" },
{ "$unwind": "$message.readBy" },
{ "$group": {
"_id": {
"user_id": "$users._id",
"thread_id": "$_id",
},
"unread_messages": {
"$sum": {
"$cond": [
{ "$ne": [ "$users._id", "$message.readBy" ] },
1,
0
]
}
}
}},
// { "$replaceRoot": { "newRoot": { "$mergeObjects": ["$_id", { "count": "$unread_messages" }]} } }
])
Aggregation results
{
"_id" : {
"user_id" : ObjectId("60d4efa6a95f446051f31491"),
"thread_id" : ObjectId("60d4efa6a95f446051f31492")
},
"unread_messages" : 4.0
},
{
"_id" : {
"user_id" : ObjectId("60d4efa6a95f446051f3148f"),
"thread_id" : ObjectId("60d4efa6a95f446051f31492")
},
"unread_messages" : 4.0
},
{
"_id" : {
"user_id" : ObjectId("60d4efa6a95f446051f31490"),
"thread_id" : ObjectId("60d4efa6a95f446051f31492")
},
"unread_messages" : 4.0
}
Results are partially OK, but, I want to keep my original structure of a document and copy aggregation results accordingly to the thread id back to the original document
I would be very grateful if you help me with the aggregation pipeline
Expected results
{
"_id": ObjectId("60d4efa6a95f446051f31492"),
"latestMessage": "Voluptatem eos officiis optio dolor est et.",
"type": "LISTING",
"users": [{
"_id": ObjectId("60d4efa6a95f446051f31491"),
"displayName": "Monique Connelly II"
},
{
"_id": ObjectId("60d4efa6a95f446051f31490"),
"displayName": "Ivory Jacobson DDS"
},
{
"_id": ObjectId("60d4efa6a95f446051f3148f"),
"displayName": "Ron Weimann"
}
],
"createdBy": "60d4efa6a95f446051f3148f",
"createdAt": ISODate("2021-06-24T20:48:38.537Z"),
"modifiedAt": ISODate("2021-06-24T20:48:38.620Z"),
"message": [...],
"stats": [{
"_id": {
"user_id": ObjectId("60d4efa6a95f446051f31491"),
"thread_id": ObjectId("60d4efa6a95f446051f31492")
},
"unread_messages": 4.0
},
{
"_id": {
"user_id": ObjectId("60d4efa6a95f446051f3148f"),
"thread_id": ObjectId("60d4efa6a95f446051f31492")
},
"unread_messages": 4.0
},
{
"_id": {
"user_id": ObjectId("60d4efa6a95f446051f31490"),
"thread_id": ObjectId("60d4efa6a95f446051f31492")
},
"unread_messages": 4.0
}
]
}

Answer 1

I post a solution that works perfectly for my case with $first + $replateRoot operations.
Final results have different ids as not in the first post that is because I re-created documents
db.threads.aggregate([
{ "$lookup": { "from": "messages", "localField": "_id", "foreignField": "threadId", "as": "message"}},
{ "$unwind": "$message" },
{ "$unwind": "$users" },
{ "$unwind": "$message.readBy" },
{ "$group": {
"_id": {
"user_id": "$users._id",
"thread_id": "$_id",
},
"thread": {
"$first": "$$ROOT"
},
"unread_messages": {
"$sum": {
"$cond": [
{ "$ne": [ "$users._id", "$message.readBy" ] },
1,
0
]
}
}
}},
{ "$group": {
"_id": "$_id.thread_id",
"thread": { "$first": "$thread" },
"stats": {
"$push": {
"userId": "$_id.user_id",
"unreadMessages": "$unread_messages"
}
}
}},
{ "$replaceRoot": { "newRoot": { "$mergeObjects": ["$thread", { stats: "$stats" }]} } }
])
Final results
/* 1 */
{
"_id" : ObjectId("60d574e242e59a48b886c586"),
"latestMessage" : "Molestias quo quod occaecati exercitationem veniam eaque.",
"type" : "LISTING",
"users" : {
"_id" : ObjectId("60d574e242e59a48b886c584"),
"displayName" : "Meggan Vandervort"
},
"unreadMessages" : NumberLong(0),
"createdBy" : "60d574e242e59a48b886c582",
"createdAt" : ISODate("2021-06-25T06:17:06.547Z"),
"modifiedAt" : ISODate("2021-06-25T06:17:06.617Z")
"message" : {
"_id" : ObjectId("60d574e242e59a48b886c58d"),
"content" : "Velit dolores vel.",
"deleted" : false,
"threadId" : ObjectId("60d574e242e59a48b886c586"),
"type" : "TEXT",
"thread" : {
"$ref" : "threads",
"$id" : ObjectId("60d574e242e59a48b886c586")
},
"readBy" : ObjectId("60d574e242e59a48b886c582"),
"attributes" : [],
"createdBy" : "60d574e242e59a48b886c582",
"createdAt" : ISODate("2021-06-25T06:17:06.595Z"),
"modifiedAt" : ISODate("2021-06-25T06:17:06.595Z")
},
"stats" : [
{
"userId" : ObjectId("60d574e242e59a48b886c584"),
"unreadessages" : 6.0
},
{
"userId" : ObjectId("60d574e242e59a48b886c583"),
"unreadessages" : 6.0
},
{
"userId" : ObjectId("60d574e242e59a48b886c582"),
"unreadessages" : 6.0
}
]
}
and more...