MongoDB nested object aggregation sum and sort - mongodb

Question

I have highly nested mongodb set of objects and i want to sort subofdocuments according to the result of sum their votes for example :
{
"_id":17846384es,
"company_name":"company1",
"products":[
{
"product_id":"123785",
"product_name":"product1",
"user_votes":[
{
"user_id":1,
"vote":1
},
{
"user_id":2,
"vote":2
}
]
},
{
"product_id":"98765",
"product_name":"product2",
"user_votes":[
{
"user_id":5,
"vote":3
},
{
"user_id":3,
"vote":3
}
]
}
]
}
i want to sort as descending products according to the result of sum their votes
the expected output is
{
"_id":17846384es,
"company_name":"company1",
"products":[
{
"product_id":"98765",
"product_name":"product2",
"user_votes":[
{
"user_id":5,
"vote":3
},
{
"user_id":3,
"vote":3
}
]
"votes":8
},
{
"product_id":"123785",
"product_name":"product1",
"user_votes":[
{
"user_id":1,
"vote":1
},
{
"user_id":2,
"vote":2
}
],
"votes":3
}
]
}
Any Idea ?

Answer 1

The following pipeline
db.products.aggregate([
{ $unwind: "$products" },
{
$project: {
company_name: 1,
products: 1,
totalVotes: {
$sum: "$products.user_votes.vote"
}
}
},
{ $sort: { totalVotes: -1 } },
{
$group: {
_id: "$_id",
company_name: { $first: "$company_name" },
products: { $push: "$products" }
}
}
])
would output
{
"_id" : "17846384es",
"company_name" : "company1",
"products" : [
{
"product_id" : "98765",
"product_name" : "product2",
"user_votes" : [
{
"user_id" : 5,
"vote" : 3
},
{
"user_id" : 3,
"vote" : 3
}
]
},
{
"product_id" : "123785",
"product_name" : "product1",
"user_votes" : [
{
"user_id" : 1,
"vote" : 1
},
{
"user_id" : 2,
"vote" : 2
}
]
}
]
}
In case you want to keep the sum of the votes at the product level as shown in your expected output simply modify the $project stage as follows
...
{
$project: {
company_name: 1,
products: {
product_id: 1,
product_name: 1,
user_votes: 1,
votes: { $sum: "$products.user_votes.vote" }
}
}
}
...