Map mongo aggregation result to array - json

Question

I have a mongo query that looks like this:
db.myCollection.aggregate([ {
$group: {
_id: null,
price: {
$sum: "$price"
},
inventory: {
$sum: "$inventory"
}
}
}])
Which returns
{
"_id" : null,
"price" : 26,
"inventory" : 5,
}
I would like a query which would rather return something like this:
[
{
name: "price",
amount: 26
},
{
name: "inventory",
amount: 5
}
]
EDIT:
How would I write this in Java with Spring Data? I can group and sum but don't know how to project it?
Aggregation aggregation = newAggregation(
group("$id")
.sum("price").as("price")
.sum("inventory").as("inventory")
);

Answer 1

You'll need to use $project. It allows us to define which fields will be returned, as well as their format.
db.myCollection.aggregate([{
$group: {
_id: null,
price: {
$sum: "$price"
},
inventory: {
$sum: "$inventory"
}
}
},
{
$project: {
_id: 0 //removes _id from result
something: [
{name: "price", amount: "$price"},
{name: "inventory", amount: "$inventory"}
]
}
}])
That will give you:
{
"something" : [
{
"name" : "price",
"amount" : 26
},
{
"name" : "inventory",
"amount" : 5
}
]
}

Answer 2

You can use below aggregation
db.collection.aggregate([
{ "$project": {
"data": {
"$map": {
"input": { "$objectToArray": "$$ROOT" },
"in": { "name": "$$this.k", "amount": "$$this.v" }
}
}
}},
{ "$unwind": "$data" },
{ "$replaceRoot": { "newRoot": "$data" }},
{ "$match": { "amount": { "$ne": null }}
}
])