MongoDB query subdocument for records that don't match criteria - mongodb

Question

I currently have the following query:
db.getCollection('conversations').aggregate([
{
$lookup: {
foreignField: "c_ID",
from: "messages",
localField: "_id",
as: "messages"
}
},
{
"$unwind": "$messages"
},
{
"$sort": {
"messages.t": -1
}
},
{
"$group": {
"_id": "$_id",
"lastMessage": {
"$first": "$messages"
},
"allFields": {
"$first": "$$ROOT"
}
}
},
{
"$replaceRoot": {
"newRoot": {
"$mergeObjects": [
"$allFields",
{
"lastMessage": "$lastMessage"
}
]
}
}
},
{
$project: {
messages: 0
}
},
{
$match: {
"members.uID": "1",
//"lastMessage.t": { $gt: ISODate("2020-02-04 20:38:02.154Z") }
}
},
{
$sort: { "lastMessage.t": 1 }
},
{
$limit: 10
},
{
$project: {
members: {
$slice: [ {
$filter: {
input : "$members", as : "member", cond : {
$ne : ["$$member.uID" , "1"]
}
}
}, 3 ]
}
}
},
])
However, I also have a field for each member, named "l", which contains a timestamp. It means someone has left a conversation and thus represents the leave date. I don't want anyone who left before the current timestamp (e.g. 1582056056) to be included in the members list. How can I do this?
EDIT:
conversations document
{
"_id" : ObjectId("5e35f2c840713a43aeeeb3d9"),
"members" : [
{
"uID" : "1",
"j" : 1580580922
},
{
"uID" : "4",
"j" : 1580580922,
“l”: 1580581982
},
{
"uID" : "5",
"j" : 1580580922
}
]
}
messages document
{
"_id" : ObjectId("5e35ee5f40713a43aeeeb1c5"),
"c_ID" : ObjectId("5e35f2c840713a43aeeeb3d9"),
"fromID" : "1",
"msg" : "What's up?",
"t" : 1580591922,
"d" : {
"4" : 1580592039
},
"r" : {
"4" : 1580592339
}
}

Answer 1

We can exclude them during $filter stage with $and and $or operators.
member.uID != 1 && (member.l == undefined || lastMessage.t < member.l)
Take a look query below.
db.conversations.aggregate([
{
$lookup: {
from: "messages",
foreignField: "c_ID",
localField: "_id",
as: "messages"
}
},
{
"$unwind": "$messages"
},
{
"$sort": {
"messages.t": -1
}
},
{
"$group": {
"_id": "$_id",
"lastMessage": {
"$first": "$messages"
},
"allFields": {
"$first": "$$ROOT"
}
}
},
{
"$replaceRoot": {
"newRoot": {
"$mergeObjects": [
"$allFields",
{
"lastMessage": "$lastMessage"
}
]
}
}
},
{
$project: {
messages: 0
}
},
{
$match: {
"members.uID": "1"
}
},
{
$sort: {
"lastMessage.t": 1
}
},
{
$limit: 10
},
{
$project: {
members: {
$slice: [
{
$filter: {
input: "$members",
as: "member",
cond: {
$and: [
{
$ne: [
"$$member.uID",
"1"
]
},
{
$or: [
{
$eq: [
"$$member.l",
undefined
]
},
{
$lt: [
"$lastMessage.t",
"$$member.l"
]
}
]
}
]
}
}
},
3
]
}
}
}
])
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