Database
[{
"_id": ObjectId("5acdb95d5ea63a27c1facf92"),
"venue": ObjectId("5acdb95d5ea63a27c1facf8c"),
"author": ObjectId("5ac8ba3582c2345af70d4658"),
"nested": {
"someField": 10
}
},
{
"_id": ObjectId("5acdb95d5ea63a27c1facf93"),
"venue": ObjectId("5acdb95d5ea63a27c1facf8c"),
"author": ObjectId("5ac8ba3582c2345af70d4658")
},
{
"_id": ObjectId("5acdb95d5ea63a27c1facf91"),
"venue": ObjectId("5acdb95d5ea63a27c1facf8c"),
"author": ObjectId("5ac8ba3582c2345af70d4658")
}
]
Query
db.collection.aggregate([{
$match: {
"venue": ObjectId("5acdb95d5ea63a27c1facf8c")
}
},
{
$group: {
_id: null,
array: {
$push: "$_id"
}
}
},
{
$project: {
_id: 0
}
}
])