Mogodb aggregation create output as {"key": "value"} from 2 arrays - mongodb

Question

I have a question about how to create output from 2 arrays one array with translation key and another with translation i would output as
"translation_key":"value"
Current output:
{
"_id" : ObjectId("5bfc0b2b30c4683f585078fb"),
"translation" : [
"hour",
"day"
],
"translation_key" : [
"HOUR_TEXT",
"DAY_TEXT"
],
"locale_id" : "EN_en"
}
OUTPUT should be :
{
"EN_en" :{
"HOUR_TEXT" :"hour",
"DAY_TEXT" :"day",
}
}

Answer 1

You can use below aggregation
You can use $range to get index from both the arrays and can create key (k) and value (v) pair for the resultant array and then finally $arrayToObject to convert resultant array into single document.
db.collection.aggregate([
{ "$replaceRoot": {
"newRoot": {
"$arrayToObject": [[
{
"k": "$locale_id",
"v": {
"$arrayToObject": {
"$map": {
"input": { "$range": [0, { "$size": "$translation_key" }] },
"in": {
"k": { "$arrayElemAt": ["$translation_key", "$$this"] },
"v": { "$arrayElemAt": ["$translation", "$$this"] }
}
}
}
}
}
]]
}
}}
])
Which returns
[
{
"EN_en": {
"DAY_TEXT": "day",
"HOUR_TEXT": "hour"
}
}
]

Answer 2

You can try below aggregation:
db.col.aggregate([
{
$project: {
array: [
{
k: "$locale_id",
v: {
$arrayToObject: {
$map: {
input: { $range: [0, { $size: "$translation" }] },
as: "index",
in: {
k: { $arrayElemAt: [ "$translation", "$$index" ] },
v: { $arrayElemAt: [ "$translation_key", "$$index" ] }
}
}
}
}
}
]
}
},
{
$replaceRoot: {
newRoot: { $arrayToObject: "$array" }
}
}
])
Basically you need to use $arrayToObject operator to manipulate your key names and in your case it should be used twice. This operator expects an array of objects with two properties k and v and therefore you should use $map to generate that values based on translation, $range is used to generate indexes to traverse translation and translation_key arrays. Then you can use $replaceRoot to promote dynamically generated key into root level of your document.
Output:
{ "EN_en" : { "hour" : "HOUR_TEXT", "day" : "DAY_TEXT" } }