How to convert to ObjectId and match dates on MongoDB lookup? - mongodb

Question

I am grabbing an id from a nested value in a schema, then using that to lookup the id from another table and also matching on a couple dates from that table. I've tried a regular match/lookup/unwind/match and also a lookup/let/pipeline technique. In both cases, it ignores matching on the date for some reason. What am I missing?
Here is one method for reference. I'm not sure where to put the sort either since it doesn't seem to pull $meeting out to sort on.
EXAMPLE RECORDS
PRODUCT
{
"_id" : ObjectId("5f36c0df6d5553e6af208cac"),
"items" : [
{
"paramType" : "Meeting",
"paramValue" : "5f36c0df6d5553e6af208cab"
}
],
"ownerId" : ObjectId("12345678901234567")
}
MEETING
{
"_id" : ObjectId("5f36c0df6d5553e6af208cab"),
"startDate" : ISODate("2020-08-18T10:00:00.000+0000"),
"endDate" : ISODate("2020-08-18T11:00:00.000+0000")
}
AGGREGATE
db.getCollection("products").aggregate(
[
{
$match: {
"ownerId": ObjectId("12345678901234567")
}
},
{
$unwind: "$items"
},
{
$lookup: {
from: "meetings",
let: { "meetingId": '$items.paramValue' },
pipeline: [
{
$match: {
$expr: {
$and: [
{ $eq: ["$_id", "$$meetingId"] },
{
$eq: ["meeting.startDate", {
"$gte": ["$meeting.startDate", ISODate("2020-08-01T00:00:00.000Z")]
}]
},
{
$eq: ["meeting.endDate", {
"$lte": ["$meeting.endDate", ISODate("2020-08-31T23:59:59.999Z")]
}]
}
],
},
},
},
],
as: "meeting"
}
},
{
$unwind: "$meeting"
},
{
$project: {
"_id": 1,
"items": 1,
"meeting": "$meeting"
}
},
{
$sort: {
'meeting.startDate': 1
}
},
]
);
It might be because item.paramValue is not converted to an ObjectId before the lookup. But can't figure out how to convert it inside an aggregate. I tried this, but no go
{
$addFields: {
"convertedMeetingId": { $toObjectId: "$items.paramValue" }
}}
let: { "meetingId": "$convertedMeetingId" }

Answer 1

There are quick fixes in $lookup other looks good,
let you can convert meetingId string to ObjectId here using $toObjectId
$gte and $lte, you used $meeting.startDate and $meeting.endDate it should be $startDate and $endDate because you are already inside meeting lookup.
i am not sure why you have used $eq and with $gte and $lte, if i am not wrong i have corrected and removed $eq it will work directly.
{
$lookup: {
from: "meetings",
let: { meetingId: { $toObjectId: "$items.paramValue" } },
pipeline: [
{
$match: {
$expr: {
$and: [
{ $eq: ["$_id", "$$meetingId"] },
{ $gte: ["$startDate", ISODate("2020-08-01T00:00:00.000Z")] },
{ $lte: ["$endDate", ISODate("2020-08-31T23:59:59.999Z")] }
]
}
}
}
],
as: "meeting"
}
},
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