MongoDB - find entries where field with specific name is present, nested anywhere - mongodb

Question

I have a mongoDB database, where some entries have a field of a name "rx" + value of another field in this entry (let's call it rxid), so the final name of this field could look like "rx1234" or "rx2836". Inside this field there is a list of dictionaries which MAY contain fields with names "A" and "B". My task is to find how many entries in this database have at least one non-empty field named A or B, no matter where it is nested. I tried to search for nested queries, however it always requires to specify the "parent" field, which in my case is a combination of rx and a value of other field, so it is not a constant name.
My database schema look something like:
{
"_id" : 1,
"rxid" 1234,
"rx1234" : [
{
"A" : "somevalue",
"B" : "someothervalue",
},
{
"A" : "somevalue2",
}
]
},
{
"_id" : 2,
"rxid" 2345
}
In this case I expect to count how many objects are structured like _id = 1 and how many like _id = 2 (there may be other fields inside but they are irrelevant)

Answer 1

Refer this
It checks for rxCustomNumber field and then checks for A/B inside that field. You can simply add a count pipeline to get the counts.
db.collection.aggregate([
{
"$project": {
"concatValue": {//Form the dynamic field dynamically
"$concat": [
"rx",
{
"$toString": "$rxid"
}
]
},
"data": {
"$objectToArray": "$$ROOT"
}
}
},
{//Restructure the field
$unwind: "$data"
},
{
$match: {
$and: [//Check for the match
{
$expr: {
"$eq": [
"$concatValue",
"$data.k"
]
}
}
]
}
},
{//Print the existence
"$project": {
"data.v.A": 1,
"data.v.B": 1
}
}
])