Query array of dictionary in mongodb - mongodb

Question

I have a collection db.orders in mongodb, this is a example:
{
"_id" : ObjectId("5ed269e0f18b5c0d33150ce1"),
"user" : ObjectId("5ed16ace5b16a6100c1ae744"),
"cart" : {
"items" : [
{
"item" : {
"_id" : "5ed16847fb395528f07f2d19",
"tipo" : "anillo",
"imagePath" : "../images/anillos/anillo1.png",
"title" : "Anillo Geo",
"description" : "Anillo en bronce con baño en oro de 24k",
"price" : 25,
"qty" : 1
}
},
{
"item" : {
"_id" : "5ed16847fb395528f07f2d2e",
"tipo" : "collar",
"imagePath" : "../images/collares/collar10.png",
"title" : "Cadenita Pendulo cuarzos naturales",
"description" : "Cadenita en bronce con baño en oro de 18k.",
"price" : 20,
"qty" : 1
}
},
{
"item" : {
"_id" : "5ed16847fb395528f07f2d26",
"tipo" : "anillo",
"imagePath" : "../images/anillos/anillo14.png",
"title" : "Anillo mandala de cristales",
"description" : "Anillo en bronce con baño en oro de 24k, incluye estuche de madera ",
"price" : 20,
"qty" : 1
}
}
],
"totalQty" : 3,
"totalPrice" : 65
},
"address" : "carrera 9/ Madrid",
"city" : "Madrid",
"name" : "Marcela R",
"paymentId" : "ch_1GoIGGByvh8EqLzfNGV02e3e",
"oderdate" : ISODate("2020-05-30T14:12:48.624Z"),
"__v" : 0
}
I need to know how many title: "Anillo geo" and generally how many cart.items.item.title have been sold. I try different methods but I end up with something like this:
{
"_id" : ObjectId("5ed27fee825300b7d182355d"),
"cart" : {
"items" : [
{
"title" : "Anillo Geo",
"price" : 25,
"qty" : 1,
"tipo" : "anillo"
},
{
"title" : "Cadenita Pendulo cuarzos naturales",
"price" : 29,
"qty" : 1,
"tipo" : "collar"
},
{
"title" : "Anillo mandala de cristales",
"price" : 29,
"qty" : 1,
"tipo" : "anillo"
}
]
}
}
But I need a query that give me something like:
{"_id" : Anillo Geo, count: 5}
{"_id" : Cadenita Pendulo cuarzos naturales, count: 8}...
Anyone have any idea of how to do this query?
Kind regards!!

Answer 1

Basically you need to unwind cart.items array & group on _id + title to count no.of titles got repeated for an _id document.
db.collection.aggregate([
{
$unwind: "$cart.items"
},
{
$group: {
_id: { _id: "$_id", title: "$cart.items.item.title" },
count: { $sum: 1 }
}
},
/** transform fields the way you want in output */
{
$project: { _id: "$_id._id", title: "$_id.title", count: 1 }
}
])
Test : mongoplayground
Note :
If possible try to use $match as first stage to do this operation on a single doc i.e; for a single user or at-least lesser docs rather than on an entire collection.