Mongodb: Search in array with $aggregate - node.js

Question

I have 2 collections. The documents looks like as follows. I have removed other properties for easy understanding:
Collection_A
{
"ref_id" : ObjectId("5e9561edf8beb57100dded8f"),
"features" : [
{
"_id" : ObjectId("5e9561edf8beb57100dded91"),
"k" : "foo",
"v" : "bar"
},
{
"_id" : ObjectId("5e9561edf8beb57100dded92"),
"k" : "foo2",
"v" : "bar2"
}
]
}
Collection_B
{
"ref_id" : ObjectId("5e9561edf8beb57100dded8f")
}
Using aggregate I am trying to find all documents in Collection_B where Collection_B.ref_id == Collection_A.ref_id and Collection_A.features == [{k:foo,v:bar},{k:foo2,v:bar2}]
Basically match supplied features array with $Collection_A.features. Aggregate should return document when all supplied features is present in $Collection_A.features.
After trying, this is the closest I have:
let aggregation_queries = [];
aggregation_queries.push({
$lookup: {
from: "Collection_A",
localField: "ref_id",
foreignField: "ref_id",
as: "Collection_A"
}
});
for(let i = 0; i< features.length; i++)
{
aggregation_queries.push({$match: { $expr: { $in : [features[i].k, "$Collection_A.features.k" ]}}});
}
let aggregateResult = Collection_BSchema.aggregate(aggregation_queries);
This only matches features.k but not features.v. I am trying to find a way to match both fetaures.k and features.v, something like $and: [{features[i].k, "$Collection_A.features.k"}, {features[i].v, "$Collection_A.features.v"}]
I have searched and tried a lot of approaches like $match with $all but doesn't seem to work because match doesn't support $all
for ex: "$match":{"$expr":{"$all":["$Collection_A.features",features]} which throws an error" Error: Unrecognized expression '$all'MongoError: Unrecognized expression".
Can someone please help with this or provide some guidance?

Answer 1

#whoami. This worked:
db.Collection_B.aggregate([
{
$lookup: {
from: "Collection_A",
let: {
refId: "$ref_id"
},
pipeline: [
{
$match: {
$expr: {
$eq: [
"$ref_id",
"$$refId"
]
}
}
},
{
"$match": {
"features": {
$all: [
{
"$elemMatch": {
"k": "foo",
"v": "bar"
}
},
{
"$elemMatch": {
"k": "foo2",
"v": "bar2"
}
}
]
}
}
}
],
as: "Collection_A"
}
}
])

Answer 2

There are couple of changes in your query, Since you're aggregating on Collection_B & wants to join Collection_B & Collection_A then in $lookup change this from: "Collection_B" to from: "Collection_A". Now you can use aggregation pipeline in $lookup which can accept multiple conditions before getting matched document from Collection_A to lookup result field Collection_A of Collection_B document :
Collection_BSchema.aggregate([
{
$lookup: {
from: "Collection_A",
let: { refId: "$ref_id" },
pipeline: [
{ $match: { $expr: { $eq: ["$ref_id", "$$refId"] } } },
{ $match: { features: { $elemMatch: { k: "foo", v: "bar" } } } },
],
as: "Collection_A",
},
},
]);
Test : MongoDB-Playground