Retrieve matched document from nested array [duplicate] - mongodb

Question

This question already has answers here:
Find in Double Nested Array MongoDB
(2 answers)
Closed 4 years ago.
I'm trying to collect all objects in a nested array where the field spec equals unknown.
The structure per document is similar to this:
{
"_id" :"5b1e73786f11e421956023c3",
"subs" : [
{
"name" : "subrepo1",
"files" : [
{
"name" : ".....",
"spec" : "Unknown"
},
{
"name" : ".....",
"spec" : "Unknown"
}
]
},
{
"name" : "subrepo2",
"files" : [
{
"name" : "file2",
"spec" : "Unknown"
},
{
"name" : ".....",
"spec" : "1234"
}
]
}
]
}
I tried the following but it doesn't work. I'm think this is in the right direction but i'm probably missing something important.
db.col.aggregate([
{$match: {'subs.files.spec': 'Unknown'}},
{$project: {
'subs.files': {$filter: {
input: '$subs.files',
//as: 'subs.files',
cond: {$eq: ['this.spec', 'FunSuite']}
}},
//_id: 0
}}
])
The expected output would be: (so ONLY the files that have spec equals to Unknown (NOT the other ones)
{
"_id" : "5b1e73786f11e421956023c3",
"subs" : [
{
"name" : "subrepo1",
"files" : [
{
"name" : ".....",
"spec" : "Unknown"
},
{
"name" : ".....",
"spec" : "Unknown"
}
]
},
{
"name" : "subrepo2",
"files" : [
{
"name" : "file2",
"spec" : "Unknown"
}
]
}
]
}

Answer 1

You need to use $filter aggregation operator which gives only the matched element from the array and escapes the other elements
db.collection.aggregate([
{
$unwind: "$subs"
},
{
$project: {
"subs.name": "$subs.name",
"subs.files": {
$filter: {
input: "$subs.files",
as: "file",
cond: {
$eq: [
"$$file.spec",
"Unknown"
]
}
}
}
}
},
{
$group: {
_id: "$_id",
subs: {
$push: "$subs"
}
}
}
])
Above will give following output
[
{
"_id": ObjectId("5a934e000102030405000000"),
"subs": [
{
"files": [
{
"name": ".....",
"spec": "Unknown"
},
{
"name": ".....",
"spec": "Unknown"
}
],
"name": "subrepo1"
},
{
"files": [
{
"name": "file2",
"spec": "Unknown"
}
],
"name": "subrepo2"
}
]
}
]
You can check the result here
And if you want to get the fields as in array then remove the $unwind and $replaceRoot stage from the pipeline
db.collection.aggregate([
{
$unwind: "$subs"
},
{
$project: {
"subs.name": "$subs.name",
"subs.files": {
$filter: {
input: "$subs.files",
as: "file",
cond: {
$eq: [
"$$file.spec",
"Unknown"
]
}
}
}
}
},
{
$unwind: "$subs.files"
},
{
$replaceRoot: {
newRoot: "$subs.files"
}
}
])
Above will give following output
[
{
"name": ".....",
"spec": "Unknown"
},
{
"name": ".....",
"spec": "Unknown"
},
{
"name": "file2",
"spec": "Unknown"
}
]

Answer 2

Try this way:
db.col.aggregate([
{
$unwind: '$subs'
},
{
$unwind: '$subs.files'
},
{
$match: {
'subs.files.spec': 'Unknown'
}
}
]);