How to filter array in nested documents in MongoDB? - mongodb

Question

I'm starting MongoDB and I have difficulties to understand how to filter some nested documents in an array. The objective if to keep only relevant data from a nested array.
Here is the data:
{
"_id": {
"$oid": "47bb"
},
"email": "myemail#gmail.com",
"orders": [
{
"orderNumber": "",
"products": [
{
"brand": "Brand 1",
"processing": {
"status": "pending"
}
}
],
"updated": {
"$date": {
"$numberLong": "1673031718883"
}
}
},
{
"orderNumber": "",
"products": [
{
"brand": "Brand 2",
"processing": {
"status": "pending"
}
}
],
"updated": {
"$date": {
"$numberLong": "1673031718883"
}
}
},
{
"orderNumber": "",
"products": [
{
"brand": "Brand 3",
"processing": {
"status": "processing"
}
}
],
"updated": {
"$date": {
"$numberLong": "1673031718883"
}
}
}
],
"privilege": {
"admin": false
},
"isVerified": {
"email": "true"
}
}
I want exactly the same data structure with 'orders.products.processing.status': 'pending'
The response from the database should be:
{
"_id": {
"$oid": "62b333644f70f94aa47bb4da"
},
"email": "myemail#gmail.com",
"orders": [
{
"orderNumber": "",
"products": [
{
"brand": "Brand 1",
"processing": {
"status": "pending"
}
}
],
"updated": {
"$date": {
"$numberLong": "1673031718883"
}
}
},
{
"orderNumber": "",
"products": [
{
"brand": "Brand 2",
"processing": {
"status": "pending"
}
}
],
"updated": {
"$date": {
"$numberLong": "1673031718883"
}
}
}
],
"privilege": {
"admin": false
},
"isVerified": {
"email": "true"
}
}
My closest attempt to a correct query is:
db.collection.aggregate([{
$unwind: '$orders'
},
{
$unwind: '$orders.products'
},
{
$match: {
"orders.products.processing.status": 'pending'
}
}, {
$group: {
_id: {
"_id": "$_id",
"email": "$email",
"orders": {
"orderNumber": "$orders.orderNumber",
"products": {
"processing": "$orders.products.processing.updated",
"brand": "$orders.products.brand",
}
},
},
products: {
$push: "$orders.products"
},
}
}, {
$project: {
products: 0,
}
}
])
The problem is that the result lose the grouping by _id and loosing the initial json structure. Thanks.

Answer 1

You can try this query:
First $match to get only documents which have orders.products.processing.status as pending (later will be filtered and maybe is redundant but using $map and $filter I prefer to avoid to do over all collection).
Then $project to get only desired values. Here the trick is to return in orders only the orders you want.
To accomplish that you can use $map to iterate over the array and return a new one with values that matches the filter (like a JS map).
And then the $filter. Here are filtered values whose status is not pending and returned to the map that output in the field orders.
And this without $unwind and $group :)
db.collection.aggregate([
{
"$match": {
"orders.products.processing.status": "pending"
}
},
{
"$project": {
"email": 1,
"isVerified": 1,
"privilege": 1,
"orders": {
"$map": {
"input": "$orders",
"as": "order",
"in": {
"orderNumber": "$$order.orderNumber",
"products": {
"$filter": {
"input": "$$order.products",
"cond": {
"$eq": [ "$$this.processing.status", "pending" ]
}
}
}
}
}
}
}
}
])
Example here
And also a bonus... check this example here I've added a one more $filter. It's so messy but if you can understand is quite easy. The $map from the first example return an array, so now I'm using a $filter ussing that array and filtering (not show) the objects where products is empty (i.e. where products.processing.status is not pending).