How to group by one matching element in a subdocument - Mongodb - mongodb

Question

Suppose I have the following collection.
[
{
"items": {
"item": [
{
"#pid": "131",
"text": "Apple"
},
{
"#pid": "61",
"text": "Mango"
},
{
"#pid": "92",
"text": "cherry"
},
{
"#pid": "27",
"text": "grape"
},
{
"#pid": "34",
"text": "dragonfruit"
}
]
},
"type": "A"
},
{
"items": {
"item": [
{
"#pid": "131",
"text": "Apple"
},
{
"#pid": "27",
"text": "grape"
},
{
"#pid": "34",
"text": "dragonfruit"
}
]
},
"type": "B"
},
{
"items": {
"item": [
{
"#pid": "131",
"text": "Apple"
}
]
},
"type": "A"
}
]
I want to get the type in which apple or mango is sold, group by item name. For the above collection, the output would be :
{
"_id": "Apple",
"items" : [
"A",
"B",
"A"
]
},
{
"_id": "Mango",
"items" : [
"A"
]
}
I tried the following query but it return nothing :
db.collection.aggregate([
{
$match : {
'items.item.text' : {$regex : 'Apple|Mango'}
}
},
{
$project : {
type : "$type"
}
},
{
$group : {
_id : '$items.item',
types : {$push : '$type'}
}
}
])
I think that even if this works, it's going to group by the entire 'items.item'. Where am I going wrong?
P.S. : I don't have the liberty to change the format of the document
Thanks a lot in advance.

Answer 1

You were on the right direction. You need to use $unwind operator and you don't need $project stage in your aggregation. The below query will be helpful:
db.collection.aggregate([
{
$unwind: "$items.item"
},
{
$match: {
"items.item.text": {
$regex: "Apple|Mango"
}
}
},
{
$group: {
_id: "$items.item.text",
type: {
$push: "$type"
}
}
}
])
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