MongoDB create an array within an array - json

Question

I am struggling to get my head around MongoDB and aggregates and groups. I've spent about 3 days so far.
I have source data that looks like...
{
"formName" : "my form",
"updatedAt" : "2021-11-02T13:29:00.123Z",
},
{
"formName" : "another form",
"lastUpdated" : "2021-10-01T13:29:00.123123",
},
Note that there are potentially different date names, though these are the only differences.
I am attempting to achieve an output of...
{
"_id": null,
"text": "my form", (NOTE: This is the formName)
"children": [{
"text" : 2021, (This is the year part of the updated)
"children" : [
{"text" : 1}, (These are the month part of the updated)
{"text" : 2},
{"text" : 3},
{"text" : 4}
]
},
]
}
So, basically a tree, which has formName, with child branch of years, with child branch of months.
I have tried all kinds of things, many don't work, such as nested $addToSet inside $groups.
I have been close, but I can't solve it.
This is the closest, but this doesn't work.
db.FormsStore.aggregate( [
{$match:{myKey:"a guid to group my forms together"}},
{$project: {formName:1, lastUpdated:1, updatedAt:1}},
{
$group: {
_id: { formName: "$formName" },
Year: {$addToSet: {$year: {$dateFromString: { dateString: "$lastUpdated" }}}},
Month: {$addToSet: {$month: {$dateFromString: { dateString: "$lastUpdated" }}}},
}
},
{
$group: {
_id: { formName: "$_id.formName" },
Time: {$addToSet: {year: "$Year", month: "$Month"}}
}
}
]
)
The output from that is showing...
{
_id: { formName: 'One of my forms' },
Time: [
{
year: [ 2021 ],
month: [ 10, 11 ]
}
]
}
This will all be used in C#
Your help would be greatly appreciated.

Answer 1

Query
adds a new field "date" with the date on Date format
group first the more specific (formname+year) to put the months in the array
group then the less specific (formname) to put the years in the array
aggregate(
[{"$set":
{"date":
{"$cond":
["$updatedAt", {"$dateFromString": {"dateString": "$updatedAt"}},
{"$dateFromString": {"dateString": "$lastUpdated"}}]},
"updatedAt": "$$REMOVE",
"lastUpdated": "$$REMOVE"}},
{"$group":
{"_id": {"text": "$formName", "year": {"$year": "$date"}},
"children": {"$push": {"text": {"$month": "$date"}}}}},
{"$group":
{"_id": "$_id.text",
"children":
{"$push": {"text": "$_id.year", "children": "$children"}}}},
{"$set": {"text": "$_id", "_id": "$$REMOVE"}}])
Edit
The bellow sorts also by year/month, and keeps only unique year/months per formName.
the difference is the group by formName,year,month to take the unique (first aacumulator will take one only of those that have the same in all 3)
replace-root (make that first document ROOT document)
and then sort by those 3 fields (descending year,ascending month)
group
sort by 2 fields
final group
PlayMongo
*mongoplaygroung loses the order of fields, run it on your driver also to be sure
aggregate(
[{"$set":
{"date":
{"$cond":
["$updatedAt", {"$dateFromString": {"dateString": "$updatedAt"}},
{"$dateFromString": {"dateString": "$lastUpdated"}}]},
"updatedAt": "$$REMOVE",
"lastUpdated": "$$REMOVE"}},
{"$set": {"year": {"$year": "$date"}, "month": {"$month": "$date"}}},
{"$group":
{"_id": {"formName": "$formName", "year": "$year", "month": "$month"},
"doc": {"$first": "$$ROOT"}}},
{"$replaceRoot": {"newRoot": "$doc"}},
{"$sort": {"formName": 1, "year": -1, "month": 1}},
{"$group":
{"_id": {"text": "$formName", "year": "$year"},
"children": {"$push": {"text": "$month"}}}},
{"$sort": {"_id.text": 1, "_id.year": -1}},
{"$group":
{"_id": "$_id.text",
"children":
{"$push": {"text": "$_id.year", "children": "$children"}}}},
{"$set": {"text": "$_id", "_id": "$$REMOVE"}}])
With data
[
{
"formName": "my form",
"updatedAt": "2021-11-02T23:30:15.123Z"
},
{
"formName": "my form",
"updatedAt": "2021-10-02T23:30:15.123Z"
},
{
"formName": "my form",
"updatedAt": "2020-06-02T23:30:15.123Z"
},
{
"formName": "my form",
"updatedAt": "2020-07-02T23:30:15.123Z"
},
{
"formName": "another form",
"updatedAt": "2021-10-01T23:30:15.123Z"
},
{
"formName": "another form",
"updatedAt": "2021-10-01T23:30:15.123Z"
},
{
"formName": "another form",
"updatedAt": "2021-09-01T23:30:15.123Z"
},
{
"formName": "another form",
"updatedAt": "2021-08-01T23:30:15.123Z"
},
{
"formName": "another form",
"updatedAt": "2020-10-01T23:30:15.123Z"
}
]
I got results
[{
"children": [
{
"text": 2021,
"children": [
{
"text": 10
},
{
"text": 11
}
]
},
{
"text": 2020,
"children": [
{
"text": 6
},
{
"text": 7
}
]
}
],
"text": "my form"
},
{
"children": [
{
"text": 2021,
"children": [
{
"text": 8
},
{
"text": 9
},
{
"text": 10
}
]
},
{
"text": 2020,
"children": [
{
"text": 10
}
]
}
],
"text": "another form"
}]

Answer 2

I continued to work on it, and while this is also not quite right (yet), here is what I came up with.
db.FormsStore.aggregate([
{$project: {formName:1, lastUpdated:1, updatedAt:1}},
{
$group: {
_id: {formName: "$formName", Year: {$year: {$dateFromString: { dateString: "$updatedAt" }}}, Month: {$month: {$dateFromString: { dateString: "$updatedAt" }}}},
}
},
{
$group: {
_id: {formName: "$_id.formName", Year: "$_id.Year"},
Months: {$addToSet: {Text: "$_id.Month"}}
}
},
{
$group: {
_id: "$_id.formName", Children: {$addToSet: {Text: "$_id.Year", Children: "$Months"}},
}
}
])
Getting all my data in the first group, then creating a set with the months in the second group, then creating a set with the years and adding the months to each year in the third group.