Matching a value in subdocument array and matching array to _id - mongodb

Question

I have a collection of Users which looks like this:
{
"_id": {
"$oid": "5ff6298f2056ad02272d10f2"
},
"name": "Billy Bob",
"story": {
"posts": [
{"id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"},
{"id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"},
{"id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"}
],
"whoCanView": [{
"$oid": "5ff891bd749ed24316272317"
}, {
"$oid": "5ffc89392056ad02272d10f3"
}]
}
}
I want to get all users and their stories listed in an array which I call "contacts". The user currently querying the collection may only get results if their userId is in the "whoCanView" array.
This is what i have so far but doesn't seem to be working:
users.find({'story' : {
'$elementMatch' : {
'_id' : {'$in' : contacts},
ObjectID(userId) : {'$in' : 'story.whoCanView'}
}
}
});
Any guidance would be appreciated. Thanks!

Answer 1

ObjectID(userId) : {'$in' : 'story.whoCanView'}
Above line along with the usage of $elemMatch operator is wrong in your code. Try this query instead:
let contacts = [
ObjectId("5ff6298f2056ad02272d10f2"),
ObjectId("5ff6298f2056ad02272d10f3"),
ObjectId("5ff6298f2056ad02272d10f4")
];
let userId = ObjectId("5ff891bd749ed24316272317");
db.users.find(
{
"_id": { $in: contacts },
"story.whoCanView": userId
},
{
"strories": "$story.posts"
}
);
Output when userId is ObjectId("5ff891bd749ed24316272317"):
/* 1 createdAt:1/7/2021, 2:50:15 AM*/
{
"_id" : ObjectId("5ff6298f2056ad02272d10f2"),
"strories" : [
{
"id" : "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"
},
{
"id" : "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"
},
{
"id" : "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"
}
]
},
/* 2 createdAt:1/7/2021, 2:50:15 AM*/
{
"_id" : ObjectId("5ff6298f2056ad02272d10f3"),
"strories" : [
{
"id" : "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"
},
{
"id" : "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"
},
{
"id" : "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"
}
]
},
/* 3 createdAt:1/7/2021, 2:50:15 AM*/
{
"_id" : ObjectId("5ff6298f2056ad02272d10f4"),
"strories" : [
{
"id" : "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"
},
{
"id" : "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"
},
{
"id" : "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45"
}
]
}
Output when userId is ObjectId("5ff891bd749ed24316272318"):
[]
Test data in users collection:
[
{
"_id": ObjectId("5ff6298f2056ad02272d10f2"),
"name": "Billy Bob",
"story": {
"posts": [
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" },
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" },
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" }
],
"whoCanView": [
ObjectId("5ff891bd749ed24316272317"),
ObjectId("5ffc89392056ad02272d10f3")
]
}
},
{
"_id": ObjectId("5ff6298f2056ad02272d10f3"),
"name": "Billy Bob",
"story": {
"posts": [
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" },
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" },
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" }
],
"whoCanView": [
ObjectId("5ff891bd749ed24316272317"),
ObjectId("5ffc89392056ad02272d10f3")
]
}
},
{
"_id": ObjectId("5ff6298f2056ad02272d10f4"),
"name": "Billy Bob",
"story": {
"posts": [
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" },
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" },
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" }
],
"whoCanView": [
ObjectId("5ff891bd749ed24316272317"),
ObjectId("5ffc89392056ad02272d10f3")
]
}
},
{
"_id": ObjectId("5ff6298f2056ad02272d10f5"),
"name": "Billy Bob",
"story": {
"posts": [
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" },
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" },
{ "id": "b4a12557-4dfa-47eb-9f27-7bbcad0f4c45" }
],
"whoCanView": [
ObjectId("5ff891bd749ed24316272317"),
ObjectId("5ffc89392056ad02272d10f3")
]
}
}
]