MongoDB Query based on value in array and return a single field - mongodb

Question

I have a collection called countries:
{
"_id" : "123456",
"enabled" : true,
"entity" : {
"name" : [
{
"locale" : "en",
"value" : "Lithuania"
},
{
"locale" : "de",
"value" : "Litauen"
}
]
}
}
I like to return only the ObjectId and the value when the locale is "en".
{"_id":"123456", "value":"Lithuania"}
Ideally renaming value to country for:
{"_id":"123456", "country":"Lithuania"}
Using a projection like:
db.countries.aggregate([
{$project:
{country: {$arrayElemAt:["$entity.name",0]}}
}
])
returns almost the desired results:
{"_id" : "1234565", "country" : { "locale" : "en", "value" : "Lithuania" } }

Answer 1

This this one:
db.collection.aggregate([
{
$set: {
country: {
$filter: {
input: "$entity.name",
cond: { $eq: [ "$this.locale", "en" ] }
}
}
}
},
{ $project: { country: { $first: "$country.value" } } },
])
See Mongo playground

Answer 2

You can try,
$reduce to iterate loop of entity.name array, $cond check locale is "en" then return value
db.collection.aggregate([
{
$project: {
country: {
$reduce: {
input: "$entity.name",
initialValue: "",
in: {
$cond: [
{ $eq: ["$$this.locale", "en"] },
"$$this.value",
"$$value"
]
}
}
}
}
}
])
Playground

Answer 3

I should have specified the MongoDB Version. Server is running 3.6.20. For that the following solution works:
db.countries.aggregate([
{
$addFields: {
country: {
$filter: {
input: "$entity.name",
cond: { $eq: [ "$$this.locale", "en" ] }
}
}
}
},
{ $project: { country: { $arrayElemAt: [["$country.value"],0] } } },
])