Aggregate using $group twice - mongodb

Question

I've read SO and questions like this one. However I'm not able to build the query I want...
Let's say I have the following data structure:
{
"CAUG" : "id1",
"action" : "actionA",
"date" : ISODate("2017-01-01"),
"hp" : 16
}
{
"CAUG" : "id1",
"action" : "actionB",
"date" : ISODate("2017-01-01"),
"hp" : 17
}
{
"CAUG" : "id1",
"action" : "actionC",
"date" : ISODate("2017-02-10"),
"hp" : 18
}
{
"CAUG" : "id2",
"action" : "actionX",
"date" : ISODate("2018-01-01"),
"hp" : 20
}...
The desired output is something like (not sure about brackets and other stuff...):
{
"CAUG" : "id1",
"timeline" : [
ISODate ("2017-01-01) {
{ "action" : "ActionA", hp : "..." }
{ "action" : "ActionB", hp : "..." }
},
ISODate ("2017-02-10) {
{ "action" : "ActionC", hp : "..." }
}
]
}
{
"CAUG" : "id2",
"timeline" : [
ISODate ("2018-01-01) {
{ "action" : "ActionX", hp : "..." }
}
]
}
At this time my (very limited) query is:
(I've tried many things like composite _id, but I'm alway stucked at some point).
db.aggregate(
[
{ $match: { something } },
{ $project: { something } },
{ $group: {
_id: '$CAUG',
"timeline": { "$push": "$$ROOT" }
}
}
]
)
The problem is I do not know how to do another $group inside timeline array... I'm stucked with the output below... Any clue please? Have a nice weekend.
{
"_id" : "1",
"timeline" : [
{
"CAUG" : "ca220491-ug43816",
"action" : "actionA",
"date" : ISODate("2016-12-21T23:00:00.000+0000")
},
{
"CAUG" : "ca220491-ug43816",
"action" : "actionB",
"date" : ISODate("2016-12-21T23:00:00.000+0000")
},
{
"CAUG" : "ca220491-ug43816",
"action" : "actionC",
"date" : ISODate("2017-02-21T23:00:00.000+0000")
}
]
}

Answer 1

Try running the following aggregate operation:
db.collection.aggregate([
{
"$group": {
"_id": {
"CAUG": "$CAUG",
"date": {
"$dateToString": {
"format": "%Y-%m-%d",
"date": "$date"
}
}
},
"docs": {
"$push": {
"action" : "$action",
"hp" : "$hp"
}
}
}
},
{
"$group": {
"_id": "$_id.CAUG",
"timeline": {
"$push": {
"date": "$_id.date",
"docs": "$docs"
}
}
}
}
])
which gives the sample output
/* 1 */
{
"_id" : "id1",
"timeline" : [
{
"date" : "2017-02-10",
"docs" : [
{
"action" : "actionC",
"hp" : 18.0
}
]
},
{
"date" : "2017-01-01",
"docs" : [
{
"action" : "actionA",
"hp" : 16.0
},
{
"action" : "actionB",
"hp" : 17.0
}
]
}
]
}
/* 2 */
{
"_id" : "id2",
"timeline" : [
{
"date" : "2018-01-01",
"docs" : [
{
"action" : "actionX",
"hp" : 20.0
}
]
}
]
}