MongoDB - Pivot data down instead of flattening with aggregation query - mongodb

Question

Can we unwind/flatten both old and new arrays and pivote data down like the below examples, consider both arrays might have different sizes and order. Looking for a solution in mongo aggregation query
Ex.1:
JSON/Object
{
"sno": "1001",
"owner": "Tim",
"old": [
{
"name": "John",
"age": "20"
},
{
"name": "Park",
"age": "40"
}
],
"new": [
{
"name": "Snow",
"age": "10"
},
{
"name": "Mike",
"age": "25"
},
{
"name": "New Rec",
"age": "55"
}
]
}
Output
sno owner current_name current_age renew_name renew_age
----------------------------------------------------------------------
1001 Tim John 20 Snow 10
1001 Tim Park 40 Mike 25
1001 Tim New Rec 55
Ex.2:
JSON/Object
{
"sno": "1001",
"owner": "Tim",
"old": [
{
"name": "John",
"age": "20"
},
{
"name": "Park",
"age": "40"
}
],
"new": [
{
"name": "Snow",
"age": "10"
}
]
}
Output
sno owner current_name current_age renew_name renew_age
----------------------------------------------------------------------
1001 Tim John 20 Snow 10
1001 Tim Park 40

Answer 1

$project to show required fields
$range to make array from 0 to total max element size of old or new array
$map to iterate loop of the above range
$arrayElemAt to select the object of the specific element from old and new array
$unwind deconstruct names array
$project to format your result and show required fields
db.collection.aggregate([
{
$project: {
sno: 1,
owner: 1,
names: {
$map: {
input: {
$range: [0,
{
$cond: [
{ $gt: [{ $size: "$old" }, { $size: "$new" }] },
{ $size: "$old" },
{ $size: "$new" }
]
}
]
},
in: {
old: { $arrayElemAt: ["$old", "$$this"] },
new: { $arrayElemAt: [ "$new", "$$this"] }
}
}
}
}
},
{ $unwind: "$names" },
{
$project: {
sno: 1,
owner: 1,
current_name: "$names.old.name",
current_age: "$names.old.age",
renew_name: "$names.new.name",
renew_age: "$names.new.age"
}
}
])
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