$match expr in same document does not work - mongodb

Question

How to transform the data using $if $else condition MongoDB
mongoPlayground
I am getting worst digging into $if $expr condition
This playground should return nothing because date is $gt then main collection but it does return me data.
So condition should say if history's date is $gt then main collection should return nothing else return the matched criteria data.

Answer 1

the first history record only is used, as it has the same _id as the history_id in the main collection
so if you check the first history document
{
"_id": ObjectId("5e4e755b380054797d9db627"),
"user_id": "5e4e74eb380054797d9db625",
"history_id": ObjectId("5e4e755b380054797d9db627"),
"date": 1587650683433,
"__v": 1
}
and your query
db.main.aggregate([
{
$lookup: {
from: "history",
localField: "history_id",
foreignField: "_id",
as: "History"
}
},
{
$unwind: "$History"
},
{
"$match": {
$expr: {
$cond: {
if: {
$eq: [
"5e4e74eb380054797d9db623",
"$History.user_id"
]
},
then: {
$and: [
{
$gt: [
"$date",
"$History.date"
]
},
{ // also, this part has no meaning as the same condition is used in the if part
$eq: [
"5e4e74eb380054797d9db623",
"$History.user_id"
]
}
]
},
else: {}
}
}
}
}
])
the if condition is not satisfied, as the user_id in history model "5e4e74eb380054797d9db625" does not equal to the specified id "5e4e74eb380054797d9db623"
so, it goes to the else part which is getting all the documents in the main collection
note: I've added some comment in the query, could you check it too?

Answer 2

If I am not wrong I guess this is what you're expecting :-
db.main.aggregate([
{
$lookup: {
from: "history",
localField: "history_id",
foreignField: "_id",
as: "History"
}
},
{
$unwind: "$History"
},
{
"$match": {
$expr: {
$and: [
{
$eq: [
"$_id",
"$History.user_id"
]
},
{
$gt: [
"$date",
"$Histoy.date"
]
}
]
}
}
}
])
Well, few modification might be needed to fulfill your need.