Esempio usando $lookup populate, lookup popola come un array, da cui $unwind.
Message.aggregate(
[
{ "$match": { "to": user } },
{ "$sort": { "date": 1 } },
{ "$group": {
"_id": "from",
"to": { "$first": "$to" },
"message": { "$first": "$message" },
"date": { "$first": "$date" },
"origId": { "$first": "$_id" }
}},
{ "$lookup": {
"from": "users",
"localField": "from",
"foreignField": "_id",
"as": "from"
}},
{ "$lookup": {
"from": "users",
"localField": "to",
"foreignField": "_id",
"as": "to"
}},
{ "$unwind": { "path" : "$from" } },
{ "$unwind": { "path" : "$to" } }
],
function(err,results) {
if (err) throw err;
return results;
}
)
