Get only last created document per id when using $in - mongodb

Question

I have 10.000 readings (documents) in MongoDB and I have an array of deviceIds. I need to get in Mongoose the lastly created document for each device.
My approach:
Reading.find({
"deviceId": { "$in": deviceIds}
},
function(err, readings) {
callback(err,readings);
}).sort({createdAt:-1}).limit(1);
This obviusly returns only one document. I need to get one per each deviceId in the deviceIds array.
EDIT 21/02/2018: Thanks to the help of #mickl I changed my code to:
Reading.aggregate([
{ $match: { "deviceId": { "$in": finalDevices} } },
{
$group: {
deviceId: "$deviceId",
maxCreatedAt: { $max: "$createdAt" }
}
}
],function(err, reading) {
if (err) {
callback(err, null);
} else {
callback(null, reading)
}
})
Now I am getting the following error: "The field 'deviceId' must be an accumulator object"

Answer 1

You can use aggregation framework's $match to filter your collection to specified devices and then use $group with $max to get the dates.
Device.aggregate([
{ $match: { "deviceId": { "$in": deviceIds} } },
{
$group: {
_id: "$deviceId",
maxCreatedAt: { $max: "$createdAt" }
}
}
],function(err, readings) {
callback(err,readings);
})