How to retrieve object values with same key inside an array - mongodb

Question

I'm trying to get (filter) all the objects from a document array that match the same key.
Document Schema example:
{
...
country: "ES",
aut_comms:
[
...
{name: "Aragon", province: "Huesca"},
{name: "Aragon", province: "Teruel"},
{name: "Aragon", province: "Zaragoza"},
{name: "Madrid", province: "Madrid"}
...
]
}
If it is possible, im tying to retrieve from the query only the values from the objects that match the same key. Resulting in an array composed like : ["Huesca", "Teruel", "Zaragoza"]
An Array of objects that match the filter will also do the trick:
[
{name: "Aragon", province: "Huesca"},
{name: "Aragon", province: "Teruel"},
{name: "Aragon", province: "Zaragoza"}
]
Thanx

Answer 1

You will be able to get this array by first unwinding the array and then manipulating it
db.demo.aggregate([
{
$unwind:"$aut_comms"
},
{
$match:{"aut_comms.name":"Aragon"}
},
{
$group:{
_id:null,
result: {$push:"$aut_comms.province"}
}
}
])

Answer 2

Edit
It is indeed possible to do such query and output in your expected format. You can do either $unwind or $match first. Personally, I prefer to do a $match first as it would limit the number of (unnecessary) documents generated by the $unwind operation.
db.getCollection('col').aggregate([
{$match: {"aut_comms.name": "Aragon"}},
{$project: {_id: 0, "aut_comms": 1}},
{$unwind: "$aut_comms"},
{$match: {"aut_comms.name": "Aragon"}},
{$project: {"province": "$aut_comms.province"}},
{$group: {
_id: null,
province: {$push: "$province"}
}}
])
The output will be:
/* 1 */
{
"_id" : null,
"province" : [
"Huesca",
"Teruel",
"Zaragoza"
]
}