MongoDb sorting documents with multiple nested arrays - mongodb

Question

There is a document with nested arrays, just want to sort collection by customerId then productList.productId and then productList.itemList.id in ascending order. MongoDb version is 3.0.14.
I've tried so far this and the query doesn't sort the collection as expected:
db.file_old.find({}, {
customerId: 1,
"productList.productId": 1,
"productList.itemList.id": 1
})
.sort({
customerId: 1,
productList: 1,
"productList.itemList": 1
})
and try aggregate framework also like this:
db.file_old.aggregate([
{"$unwind": "$productList"} ,
{"$sort": {"customerId": 1, "productList.productId": 1}}
])
It work fine for two field but if try to adding "productList.itemList.id" doesn't work, like this:
db.file_old.aggregate([
{"$unwind": "$productList"} ,
{"$sort": {"customerId": 1, "productList.productId": 1, "productList.itemList.id": 1}}
])
Collection structure:
{
"_id" : ObjectId("5f33cc2a1e84082968132324"),
"customerId" : 2196,
"productList" : [
{
"productId" : 7531,
"itemList" : [
{
"id" : 144
},
{
"id" : 145
}
]
},
{
"productId" : 7534,
"itemList" : [
{
"id" : 1244
},
{
"id" : 1243
},
{
"id" : 1245
},
{
"id" : 1242
}
]
}
]
},{
"_id" : ObjectId("5f33cc2a1e84082968132326"),
"customerId" : 2201,
"productList" : [
{
"productId" : 101201,
"itemList" : [
{
"id" : 863
},
{
"id" : 865
},
{
"id" : 862
}
]
},
{
"productId" : 7537,
"itemList" : [
{
"id" : 982
},
{
"id" : 1002
},
{
"id" : 896
}
]
}
]
}

Answer 1

You can not sort directly array, first requires to unwind(deconstruct) and then sort will apply, lets see step by step,
productList
deconstruct array ($unwind)
itemList
deconstruct array ($unwind)
sort by id ($sort)
re-construct array ($group)
sort by productId ($sort)
re-construct productList ($group)
sort by customerId ($sort)
$unwind deconstruct productList array
db.collection.aggregate([
{ $unwind: "$productList" },
$unwind deconstruct productList.itemList array
{ $unwind: "$productList.itemList" },
$sort by productList.itemList.id ascending order
{ $sort: { "productList.itemList.id": 1 } },
$group by all 3 main level of ids and re-construct itemList array
{
$group: {
_id: {
_id: "$_id",
customerId: "$customerId",
productId: "$productList.productId"
},
itemList: { $push: "$productList.itemList" }
}
},
$sort by productId ascending order
{ $sort: { "_id.productId": 1 } },
$group by main 2 level of ids and re-construct productList array
{
$group: {
_id: {
_id: "$_id._id",
customerId: "$_id.customerId"
},
productList: {
$push: {
productId: "$_id.productId",
itemList: "$itemList"
}
}
}
},
$project to show required fields
{
$project: {
_id: "$_id._id",
customerId: "$_id.customerId",
productList: 1
}
},
$sort by customerId id
{ $sort: { customerId: 1 } }
])
Playground