What wrong with my mongo query to get a specific by nest document? - mongodb

Question

{
"_id" : ObjectId("5dbdacc28cffef0b94580dbd"),
"owner" : {
"image" : "https://lh3.googleusercontent.com/a-/AAuE7mCpG2jzbEdffPgdeVWnkBKwyzCCwEB1HMbU1LAVAg=s50",
"fullname" : "soeng kanel",
"userID" : "5da85558886aee13e4e7f044"
},
"image" : "soeng kanel-1572711618984.png",
"body" : "sdadadasdsadadas sds",
"date" : ISODate("2019-11-02T16:20:05.558Z"),
"comments" : [
{
"user" : "5da85558886aee13e4e7f044",
"fullname" : "soeng kanel",
"username" : "",
"comment" : "sdsfdsfdsfds",
"_id" : ObjectId("5dbdacc78cffef0b94580dbf"),
"replies" : [
{
"likes" : [
"5da85558886aee13e4e7f044"
],
"date" : ISODate("2019-11-02T16:20:05.558Z"),
"_id" : ObjectId("5dbdacd78cffef0b94580dc0"),
"reply" : "r1111111",
"username" : "",
"fullname" : "soeng kanel",
"user" : "5da85558886aee13e4e7f044"
},
{
"likes" : [],
"date" : ISODate("2019-11-02T16:20:05.558Z"),
"_id" : ObjectId("5dbdacdb8cffef0b94580dc1"),
"reply" : "r222222",
"username" : "",
"fullname" : "soeng kanel",
"user" : "5da85558886aee13e4e7f044"
},
{
"likes" : [],
"date" : ISODate("2019-11-03T03:04:23.528Z"),
"_id" : ObjectId("5dbe4749fa751f05afcc1bd6"),
"reply" : "33333333",
"username" : "",
"fullname" : "soeng kanel",
"user" : "5da85558886aee13e4e7f044"
}
],
"date" : ISODate("2019-11-02T16:20:05.558Z"),
"likes" : []
}
],
"likes" : [
"5da85558886aee13e4e7f044"
],
"project" : {},
"__v" : 2
}
My query is
db.getCollection("posts").aggregate([
{ $match: {_id: ObjectId("5dbdacc28cffef0b94580dbd"), "comments._id": ObjectId("5dbdacc78cffef0b94580dbf") }},
{ $unwind: "$comments"},
{ $match: { "comments._id": ObjectId("5dbdacc78cffef0b94580dbf")}},
{ $project: {"replies": "$comments.replies", _id: 0}},
{ $match: { "replies._id": ObjectId("5dbdacd78cffef0b94580dc0")}},
{ $project: {"likes": "$replies.likes", _id: 0}},
])
With this query I get 3 elements ,
{
"likes" : [
[
"5da85558886aee13e4e7f044"
],
[],
[]
]
}
That is not what I want, what I want is to get by specific
replies by this _id 5dbdacd78cffef0b94580dc0.
And My expectation
{
"likes" : [
[
"5da85558886aee13e4e7f044"
]
]
}

Answer 1

Try using $unwind on replies before you $match stage on replies.
db.collection.aggregate([
{
$match: {
_id: ObjectId("5dbdacc28cffef0b94580dbd"),
"comments._id": ObjectId("5dbdacc78cffef0b94580dbf")
}
},
{
$unwind: {
path: "$comments",
preserveNullAndEmptyArrays: false
}
},
{
$match: {
"comments._id": ObjectId("5dbdacc78cffef0b94580dbf")
}
},
{
$project: {
"replies": "$comments.replies",
_id: 0
}
},
{
$unwind: {
path: "$replies",
preserveNullAndEmptyArrays: false
}
},
{
$match: {
"replies._id": ObjectId("5dbdacd78cffef0b94580dc0")
}
},
{
$project: {
"likes": "$replies.likes"
}
}
])
Above query produce output in the following fashion:
[
{
"likes": [
"5da85558886aee13e4e7f044"
]
}
]
I hope that's okay.