Mongo search Array with ONLY one match in $or - mongodb

Question

I have an array of objects to search. I want to ensure that ONLY ONE MATCH in a list of elements is returned. The following works to find if ANY of the elements in the array matches:
db.users.find({
$or:[
{ subscriberOf:{ $elemMatch:{ town: ObjectId( '58252a796f1aaf645c94f00e' )} } },
{ subscriberOf:{ $elemMatch:{ town: ObjectId( '58252a796f1aaf645c94f02d' )} } },
{ subscriberOf:{ $elemMatch:{ town: ObjectId( '58252a7d6f1aaf645c94f2cf' )} } },
{ subscriberOf:{ $elemMatch:{ town: ObjectId( '58252a7b6f1aaf645c94f132' )} } },
{ subscriberOf:{ $elemMatch:{ town: ObjectId( '58252a796f1aaf645c94f02f' )} } }
]
})
However, records can have more than one of these ids, and I want to isolate to ensure that only one of these matches. Please note that these particular 5 matches that we care about are a subset of a list that is over 2,000 strong.
In other words, I need to match ONLY ONE of these - and don't care if they match the other 2,000. That's why I can't use a "subscriberOf.1":{$exists:false}, to weed these out.
I can run multiple queries manually, if I can figure out how - maybe do a specific match on one id, then a $nor on the rest?
Any help would be appreciated.

Answer 1

Please try this :
var inputArr = [
ObjectId("58252a796f1aaf645c94f02f"),
ObjectId("58252a7b6f1aaf645c94f132"),
ObjectId("58252a7d6f1aaf645c94f2cf"),
ObjectId("58252a796f1aaf645c94f02d"),
ObjectId("58252a796f1aaf645c94f00e")
]
db.yourCollectionName.aggregate([{ $addFields: { matchingCount: { $size: { $setIntersection: ["$subscriberOf.town", inputArr] } } } },
{ $match: { matchingCount: 1 } }, {$project : {matchingCount:0}}])
Collection Data :
/* 1 */
{
"_id" : ObjectId("5e0be0f9400289966e8c9bb8"),
"subscriberOf" : {
"town" : [
ObjectId("58252a796f1aaf645c94f00e")
]
}
}
/* 2 */
{
"_id" : ObjectId("5e0be106400289966e8c9da2"),
"subscriberOf" : {
"town" : [
ObjectId("58252a796f1aaf645c94f02d")
]
}
}
/* 3 */
{
"_id" : ObjectId("5e0be2ab400289966e8ce29b"),
"subscriberOf" : {
"town" : [
ObjectId("58252a7d6f1aaf645c94f2cf")
]
}
}
/* 4 */
{
"_id" : ObjectId("5e0be2d7400289966e8cea84"),
"subscriberOf" : {
"town" : [
ObjectId("58252a7b6f1aaf645c94f132")
]
}
}
/* 5 */
{
"_id" : ObjectId("5e0be2eb400289966e8cee3b"),
"subscriberOf" : {
"town" : [
ObjectId("58252a796f1aaf645c94f02f")
]
}
}
/* 6 */
{
"_id" : ObjectId("5e0be303400289966e8cf210"),
"subscriberOf" : {
"town" : [
ObjectId("58252a796f1aaf645c94f02f"),
ObjectId("58252a7b6f1aaf645c94f132")
]
}
}
/* 7 */
{
"_id" : ObjectId("5e0be327400289966e8cf92a"),
"subscriberOf" : {
"town" : [
ObjectId("58252a796f1aaf645c94f02f"),
ObjectId("58252a7b6f1aaf645c94f132"),
ObjectId("58252a7d6f1aaf645c94f2cf"),
ObjectId("58252a796f1aaf645c94f02d"),
ObjectId("58252a796f1aaf645c94f00e")
]
}
}
Result :
/* 1 */
{
"_id" : ObjectId("5e0be0f9400289966e8c9bb8"),
"subscriberOf" : {
"town" : [
ObjectId("58252a796f1aaf645c94f00e")
]
}
}
/* 2 */
{
"_id" : ObjectId("5e0be106400289966e8c9da2"),
"subscriberOf" : {
"town" : [
ObjectId("58252a796f1aaf645c94f02d")
]
}
}
/* 3 */
{
"_id" : ObjectId("5e0be2ab400289966e8ce29b"),
"subscriberOf" : {
"town" : [
ObjectId("58252a7d6f1aaf645c94f2cf")
]
}
}
/* 4 */
{
"_id" : ObjectId("5e0be2d7400289966e8cea84"),
"subscriberOf" : {
"town" : [
ObjectId("58252a7b6f1aaf645c94f132")
]
}
}
/* 5 */
{
"_id" : ObjectId("5e0be2eb400289966e8cee3b"),
"subscriberOf" : {
"town" : [
ObjectId("58252a796f1aaf645c94f02f")
]
}
}
Note : Returning only docs where exactly one matches, 6 & 7 are not retained.
Ref : Aggregation-pipeline-operators

Answer 2

MongoDB aggregation offers better solution to achieve that.
First, we extend array into single document with $unwind. Then we apply $matchstage to filter desired id's. In the last stage, we $group with accumulator operator $addToSet to create array with unique values.
db.collection.aggregate([
{
$unwind: "$subscriberOf"
},
{
$match: {
"subscriberOf.town": {
$in: [
ObjectId("58252a796f1aaf645c94f00e"),
ObjectId("58252a796f1aaf645c94f02d"),
ObjectId("58252a7d6f1aaf645c94f2cf"),
ObjectId("58252a7b6f1aaf645c94f132"),
ObjectId("58252a796f1aaf645c94f02f")
]
}
}
},
{
$group: {
_id: "$_id",
subscriberOf: {
$addToSet: "$subscriberOf"
}
}
}
])
MongoPlayground
EDIT: If you want to export the result, follow these steps:
Iterate with .forEach method aggregation cursor to retrieve all values.
Create .js file (for instance export.js) with your aggregation, wrap it inside a function like this:
function exporter(){
db.collection.aggregate(...).forEach(function(doc){
printjson(doc);
}
})
exporter();
Now, call mongo with js file and redirect output into file from cmd / command shell:
path\to\mongo\mongo[.exe] --quiet [-u username -p password] [host:port/]database export.js > export.csv 2>&1