MongoDB Inner Array Query - mongodb

Question

I have the following Mongo Document. I need the output for all SID =100 as shown. How can this be achieved. Tried different ways.
As seen, there are multiple array levels. The input has collection of SIDs with all products.
Input
[
{
"_id": "123456",
"Continent": {
"Country": [
[
"US",
{
"State": [
[
100,
{
"Product": "Corn",
"SID": 100
}
],
[
200,
{
"Product": "Maze",
"SID": 200
}
],
[
100,
{
"Product": "Corn-HB",
"SID": 100
}
]
],
}
]
]
}
}
]
Here the out has only the collection of SID = 100, but it preserves the input format
Output
[
{
"_id": "123456",
"Continent": {
"Country": [
[
"US",
{
"State": [
[
100,
{
"Product": "Corn",
"SID": 100
}
],
[
100,
{
"Product": "Corn-HB",
"SID": 100
}
]
],
}
]
]
}
}
]

Answer 1

As mentioned in the question comments, this data design is a bit odd but a solution can be achieved using the $function function (starting in v4.4 Sep 2020) which avoids maps of maps of reduce, etc.:
var keeper_sid = 100;
db.foo.aggregate([
{$replaceRoot: {newRoot: {$function: {
body: function(obj, keeper) {
var country_arr = obj['Continent']['Country'];
for(var n1 = 0; n1 < country_arr.length; n1++) {
var tuple1 = country_arr[n1];
var state_arr = tuple1[1]['State'];
// Walk the State array backwards to ease deletions.
for(var n2 = state_arr.length - 1; n2 >= 0; n2--) {
var tuple2 = state_arr[n2];
if(tuple2[1]['SID'] != keeper) {
state_arr.splice(n2,1);
}
}
}
return obj;
},
args: [ "$$ROOT", keeper_sid ],
lang: "js"
}}
}}
]);
This is straightforward but it does make assumptions about the structure e.g. extracting the second ([1]) item from the "tuples." The code can be reduced a bit more but intermediate variables (tuple1,2) are shown to make the whole thing a little more clear.