mongodb aggregation with multiple sub groups - mongodb

Question

I have a collection with documents that look similar to this:
[
{
"_id": ObjectId("..."),
"date": ISODate("..."),
"type": "TypeA",
"color": "ColorA",
"soldFor": 12.15
},
{
"_id": ObjectId("..."),
"date": ISODate("..."),
"type": "TypeA",
"color": "ColorB",
"soldFor": 13.15
},
{
"_id": ObjectId("..."),
"date": ISODate("..."),
"type": "TypeB",
"color": "ColorA",
"soldFor": 12.15
},
{
"_id": ObjectId("..."),
"date": ISODate("..."),
"type": "TypeB",
"color": "ColorB",
"soldFor": 12.15
}
]
I know that this is not a good way to store such information, but unfortunately I have no influence in that.
What I need to get out of the collection is something like this:
[
2017: {
typeA: {
colorA: {
sum: 125.00
},
colorB: {
sum: 110.00
}
},
typeB: {
colorA: {
sum: 125.000
}
}
},
2016: {
typeA: {
colorB: {
sum: 125.000
}
}
}
]
At the moment I have two group stages that give me everything grouped by year, but I have no clue how to get the two other sub-groups. Building the sum would be a nice to have, but I am certain that I can figure out how that would be done in a group.
So far my pipeline looks like this:
[
{
$group: {
_id: { type: '$type', color: '$color', year: { $year: '$date' } },
docs: {
$push: '$$ROOT'
}
}
},
{
$group: {
_id: { year: '$_id.year' },
docs: {
$push: '$$ROOT'
}
}
}
]
which results in something like this:
[
{
"_id": {
"year": 2006
},
"docs": {
"_id": {
"type": "typeA",
"color": "colorA",
"year": 2006
},
"docs": [
{
... root document
}
]
}
},
{
"_id": {
"year": 2016
},
"docs": [
{
"_id": {
"type": "typeA",
"color": "colorB",
"year": 2016
},
"docs": [
{
... root document
}
]
}
... more docs with three keys in id
]
}
]
Help is much appreciated!

Answer 1

Using a cohort of operators found in MongoDB 3.4.4 and newer, i.e. $addFields, $arrayToObject and $replaceRoot, you can compose a pipeline like the following to get the desired result:
[
{ "$group": {
"_id": {
"year": { "$year": "$date" },
"type": "$type",
"color": "$color"
},
"count": { "$sum": "$soldFor" }
} },
{ "$group": {
"_id": {
"year": "$_id.year",
"type": "$_id.type"
},
"counts": {
"$push": {
"k": "$_id.color",
"v": { "sum": "$count" }
}
}
} },
{ "$addFields": {
"counts": { "$arrayToObject": "$counts" }
} },
{ "$group": {
"_id": "$_id.year",
"counts": {
"$push": {
"k": "$_id.type",
"v": "$counts"
}
}
} },
{ "$addFields": {
"counts": { "$arrayToObject": "$counts" }
} },
{ "$group": {
"_id": null,
"counts": {
"$push": {
"k": { "$substr": ["$_id", 0, -1 ]},
"v": "$counts"
}
}
} },
{ "$replaceRoot": {
"newRoot": {
"$mergeObjects": [
{ "$arrayToObject": "$counts" },
"$$ROOT"
]
}
} },
{ "$project": { "counts": 0 } }
]