Searching in nested arrays Mongodb - node.js

Question

I have a mongodb with some JSON data which includes and nested arrays. I am
trying to make a query to count how many documents have a specific
value. For example here is how my json data looks:
{
"_id" : ObjectId("5ecb815bf4b8512918224e71"),
"array1" : [
{
"_id" : ObjectId("5ecb815bf4b8512918224e85"),
"xxxx" : "1450",
"yyyy" : 83,
"array2" : [
{
"_id" : ObjectId("5ecb815bf4b8512918224e88"),
"aaaa" : "1470420945276",
},
{...},
{...}]
}
The query that i am trying is the following:
db.example.aggregate([
{
$project: {
value1: {
$filter: {
input: "$array1",
as: "array",
cond: { $eq: [ "$$array.array2.aaaa" , "1470420945276" ] }
}
}
}
},
{
$project: {
value1Count: { $size: "$value1" }
}
}
])
But doesnt work and returns that value1Count=0. It looks like it doesnt nnavigate into the array2 to
read the value of the 'aaaa'. Any help?

Answer 1

You were almost close to getting the desired value. The problem is $$array.array2.aaaa returns an array value, so we can't use $eq here. Instead, we should use $in operator.
db.example.aggregate([
{
$project: {
value1: {
$filter: {
input: "$array1",
as: "array",
cond: {
$in: [
"1470420945276",
"$$array.array2.aaaa"
]
}
}
}
}
},
{
$project: {
value1Count: {
$size: "$value1"
}
}
}
])
MongoPlayground | Alternative solution