mongo count rows from an array of provided data - mongodb

Question

I have collection like this:
{
"_id" : ObjectId("4d663451d1e7242c4b68e000"),
"topic" : "abc",
"subLevel" : {
"id" : 1
}
}
{
"_id" : ObjectId("4d6634514cb5cb2c4b69e000"),
"topic" : "bce",
"subLevel" : {
"id" : 1
}
}
{
"_id" : ObjectId("4d6634514cb5cb2c4b70e000"),
"topic" : "bec",
"subLevel" : {
"id" : 2
}
}
{
"_id" : ObjectId("4d6634514cb5cb2c4b70e000"),
"topic" : "vvv",
"subLevel" : {
"id" : 3
}
}
and I need to count how many documents exist for provided subLevel.id list, for example if I provide 1 and 2 it should show me that for 1 we have 2 documents and for 2 only 1 document and simply omit document where subLevel.id is 3 as it's not in the list of id's.
I tried to do it with a aggregate
db.getCollection('products').aggregate( [
{ $project:
{ "has_sublevel" : {$in: [ "subLevel.id", [1 , 2 ]]} }
},
{ $group: { _id : "$subLevel.id", count: { $sum: 1 } } }
] )
but result is
{
_id : null,
count: 4
}
how can I do it, thanks in advance!
If transform it to SQL which I familiar more, query should look like this:
select subLevelId, count(id) FROM products where subLevelId in (1,2) group by subLevelId

Answer 1

If I've understand correctly, you are so so close, check this query:
First use $match to get only documents whose subLevel.id is 1 or 2.
Then, as you have done, $group by the id and sum to get total count:
db.collection.aggregate([
{
"$match": { "subLevel.id": { "$in": [ 1, 2 ] } }
},
{
"$group": { "_id": "$subLevel.id", "count": { "$sum": 1 } }
}
])
Example here

Answer 2

You will need this:
db.products.aggregate([ {$match:{ "subLevel.id":{ $in:[1,2] } }} , {$group:{ _id:"$subLevel.id" , count:{$sum:1} } } ])
which is same like:
db.products.aggregate([ {$match:{ $or:[{"subLevel.id":1},{"subLevel.id":2} ]}} , {$group:{ _id:"$subLevel.id" , count:{$sum:1} } } ])

Answer 3

You need to push the respective docs into their respective arrays and then get their sizes:
db.collection.aggregate([
{
"$match": {
"subLevel.id": {
$in: [
1,
2
]
}
}
},
{
$group: {
"_id": "$subLevel.id",
ids: {
$push: "$_id"
}
}
},
{
$project: {
_id: false,
ids: {
$size: "$ids"
}
}
}
])
Playgroud: https://mongoplayground.net/p/J1ei37l1K5-