I have a document structures like this :
{
"_id": xxxxx,
"Name": "John Doe",
"Grades":[
{
"Physics":89,
},
{
"Math":45
},
{
"Chemistry":57
}
]
}I would like to project grades as an array of only the subjects that have over 60.
I tried this but this didn't work:
$arrayElemAt: [{ $objectToArray: { $gte: ['$hhEthGrp',60] } }, 0]
You definitely need $objectToArray to access a values for unknown keys but you also need $filter for outer array and $anyElementTrue along with $map to determine where there's any value for unknown key which has value over 60:
db.collection.aggregate([
{
$addFields: {
Grades: {
$filter: {
input: "$Grades",
cond: {
$let: {
vars: { kv: { $objectToArray: "$$this" } }
in: {
$anyElementTrue: {
$map: {
input: "$$kv.v",
in: {
$gt: [ "$$this", 60 ]
}
}
}
}
}
}
}
}
}
}
])
