Multiple $group in mongoDB - node.js

Question

I have in mongodb differents records. I write down a little example:
{_id:"sad547er4w2v5x85b8", name:"Jhon", jobTime:600, floor:2, dept:5, age:25},
{_id:"xcz547wer4xcvcx1g2", name:"Alex", jobTime:841, floor:4, dept:1, age:55},
{_id:"xcnwep2321954ldfsl", name:"Alice", jobTime:100, floor:3, dept:3, age:55},
{_id:"23s3ih94h548jhfk2u", name:"Anne", jobTime:280, floor:2, dept:8, age:22},
{_id:"03dfsk9342hjwq1503", name:"Alexa", jobTime:355, floor:2, dept:6, age:25}
I tried to obtain this output, but I don't know how to group by twice to get that structure.
{[
{age:22, floors:[{floor:2,persons:[{name:"Anne",jobTime:280,dept:8}]}]},
{age:25, floors:[{floor:2,persons:[{name:"Jhon",jobTime:600,dept:5},{name:"Alexa",jobTime:355,dept:6}]}]},
{age:55, floors:[{floor:3,persons:[{name:"Alex",jobTime:841,dept:1}]},{floor:4,persons:[{name:"Alice",jobTime:100,dept:3}]}]}
]}

Answer 1

Exactly. Use "two" $group stages
collection.aggregate([
{ "$group": {
"_id": {
"age": "$age",
"floor": "$floor",
},
"persons": { "$push": {
"name": "$name",
"jobTime": "$jobTime",
"dept": "$dept"
}}
}},
{ "$group": {
"_id": "$_id.age",
"floors": { "$push": {
"floor": "$_id.floor",
"persons": "$persons"
}}
}}
],function(err,results) {
// deal with results here
})
Which produces:
{
"_id" : 25,
"floors" : [
{ "floor" : 2,
"persons" : [
{ "name" : "Jhon", "jobTime" : 600, "dept" : 5 },
{ "name" : "Alexa", "jobTime" : 355, "dept" : 6 }
]
}
]
},
{
"_id" : 55,
"floors" : [
{ "floor" : 3,
"persons" : [
{ "name" : "Alice", "jobTime" : 100, "dept" : 3 }
]
},
{ "floor" : 4,
"persons" : [
{ "name" : "Alex", "jobTime" : 841, "dept" : 1 }
]
}
]
},
{
"_id" : 22,
"floors" : [
{ "floor" : 2,
"persons" : [
{ "name" : "Anne", "jobTime" : 280, "dept" : 8 }
]
}
]
}
So the initial $group is on a compound key including the detail down to the items you want to add to the initial "array", for "persons". Then the second $group takes only part of the initial _id for it's key and again "pushes" the content into a new array.