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Is there a MongoDB query to concatenate deep sub-lists?
Concatenate deep sub-lists using aggregate() along with $unwind. Let us create a collection with documents −
> db.demo70.insertOne(
... {
...
... "first" : [
... {
... "details" : {
... "second" : [
... {
... "StudentDetails" : {
... "Score" : 10
... }
... },
... {
... "StudentDetails" : {
... "Score" : 20
... }
... },
... {
... "StudentDetails" : {
... "Score" : 30
... }
... }
... ]
... }
... },
... {
... "details" : {
... "second" : [
... {
... "StudentDetails" : {
... "Score" : 11
... }
... },
... {
... "StudentDetails" : {
... "Score" : 18
... }
... },
... {
... "StudentDetails" : {
... "Score" : 29
... }
... }
... ]
... }
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e29ad4d0912fae76b13d76d")
}Display all documents from a collection with the help of find() method −
> db.demo70.find().pretty();
This will produce the following output −
{
"_id" : ObjectId("5e29ad4d0912fae76b13d76d"),
"first" : [
{
"details" : {
"second" : [
{
"StudentDetails" : {
"Score" : 10
}
},
{
"StudentDetails" : {
"Score" : 20
}
},
{
"StudentDetails" : {
"Score" : 30
}
}
]
}
},
{
"details" : {
"second" : [
{
"StudentDetails" : {
"Score" : 11
}
},
{
"StudentDetails" : {
"Score" : 18
}
},
{
"StudentDetails" : {
"Score" : 29
}
}
]
}
}
]
}Following is the query to concatenate deep sub-lists −
> db.demo70.aggregate([
... { $unwind: "$first" },
... { $unwind: "$first.details.second" },
... { $sort: { "first.details.second.StudentDetails.Score": -1 } },
... { $limit: 3 },
... { $replaceRoot: { newRoot: "$first.details.second.StudentDetails" } },
... { $sort: { "Score": 1 } }
... ]);This will produce the following output −
{ "Score" : 20 }
{ "Score" : 29 }
{ "Score" : 30 }
Updated on: 30-Mar-2020
51 Views
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