MongoDB aggregation get value from path containing variable - mongodb

Question

I have a collection datas like this:
[
{
"_id": 0,
"languages": { "en": true },
"translated_data": { "en": { "title": "eng title 1" } }
},
{
"_id": 1,
"languages": { "en": true },
"translated_data": { "en": { "title": "eng title 2" } }
}
]
And I need to transform it to a format like this:
[
{
"_id": 0,
"translations": [{ "language": "en", "data": { "title": "eng title 1" } }]
},
{
"_id": 1,
"translations": [{ "language": "en", "data": { "title": "eng title 2" } }]
}
]
I tried this update query but stuck
db.datas.updateMany({}, [
{
$set: {
translations: {
$map: {
input: {
$filter: {
input: {
$objectToArray: "$languages",
},
as: "language",
cond: { $eq: ["$$language.v", true] },
},
},
as: "language",
in: {
language: "$$language.k",
data: "???", // get value from $translated_data[$$language.k]
},
},
},
},
},
{
$unset: ["languages", "translated_data"],
},
]);

Answer 1

Try this:
db.datas.updateMany({},
[
{
$set: {
"translate_ok": {
$first: {
$map: {
input: { $objectToArray: "$languages" },
as: "language",
in: { $eq: ["$$language.v", true] },
}
}
}
}
},
{
$set: {
translations: {
$map: {
input: { $objectToArray: "$translated_data" },
as: "language",
in: {
$cond: [
"$translate_ok",
{
language: "$$language.k",
data: "$$language.v"
},
{
$arrayToObject: [["$$language"]]
}
]
}
}
}
}
},
{
$unset: ["languages", "translated_data", "translate_ok"]
}
]
);
Output:
/* 1 */
{
"_id" : 1,
"translations" : [
{
"language" : "en",
"data" : {
"title" : "eng title 1"
}
}
]
},
/* 2 */
{
"_id" : 2,
"translations" : [
{
"en" : {
"title" : "eng title 2"
}
}
]
}
My test data:
/* 1 */
{
"_id" : 1,
"languages" : {
"en" : true
},
"translated_data" : {
"en" : {
"title" : "eng title 1"
}
}
},
/* 2 */
{
"_id" : 2,
"languages" : {
"en" : false
},
"translated_data" : {
"en" : {
"title" : "eng title 2"
}
}
}