Fill missing records in mongo aggregate - node.js

Question

I have a collection request
{
_Id: '5b8c0f3204a10228b00a1745,
createdAt: '2018-09-07T17:18:40.759Z',
type: "demo" , //["demo","free-try","download",...]
}
And I have a query for fetching the daily number for a specific type.
Query
Model.aggregate([
{
$match: { $expr: { $and: filters } },
},
{
$project: {
day: { $substr: ["$createdAt", 0, 10] },
type: 1,
createdAt: 1,
},
},
{
$group: {
_id: {
day: "$day",
type: "$type",
},
total: { $sum: 1 },
},
},
{
$sort: { _id: 1 },
},
{
$project: {
_id: "$_id.day",
date: "$_id.day",
type: "$_id.type",
total: 1,
},
}
])
So I get these results :
[
{
"total": 1,
"_id": "2021-01-06",
"date": "2021-01-06",
"type": "print"
},
{
"total": 1,
"_id": "2021-01-13",
"date": "2021-01-13",
"type": "download"
},
{
"total": 1,
"_id": "2021-03-09",
"date": "2021-03-09",
"type": "test"
},
{
"total": 2,
"_id": "2021-03-29",
"date": "2021-03-29",
"type": "demo"
},
{
"total": 1,
"_id": "2021-04-20",
"date": "2021-04-20",
"type": "test"
},
{
"total": 1,
"_id": "2021-04-21",
"date": "2021-04-21",
"type": "download"
},
{
"total": 1,
"_id": "2021-04-21",
"date": "2021-04-21",
"type": "renew"
},
{
"total": 1,
"_id": "2021-04-22",
"date": "2021-04-22",
"type": "print"
},
{
"total": 2,
"_id": "2021-04-26",
"date": "2021-04-26",
"type": "renew"
},
{
"total": 1,
"_id": "2021-05-03",
"date": "2021-05-03",
"type": "test"
},
{
"total": 1,
"_id": "2021-05-05",
"date": "2021-05-05",
"type": "print"
},
{
"total": 1,
"_id": "2021-05-05",
"date": "2021-05-05",
"type": "test"
},
{
"total": 2,
"_id": "2021-05-31",
"date": "2021-05-31",
"type": "demo"
},
{
"total": 1,
"_id": "2021-06-03",
"date": "2021-06-03",
"type": "renew"
}
]
up to here, everything is fine, but when I need to fill the missing record, so for example if in '2021-06-03' I don't have any request of type "demo" I need to insert this object with a total of 0
{
"total": 0,
"_id": "2021-05-31",
"date": "2021-05-31",
"type": "demo"
}
so I add this pipeline based on a solution proposed in here
Model.aggregate([
{
$match: { $expr: { $and: filters } },
},
{
$project: {
day: { $substr: ["$createdAt", 0, 10] },
type: 1,
createdAt: 1,
},
},
{
$group: {
_id: {
day: "$day",
type: "$type",
},
total: { $sum: 1 },
},
},
{
$sort: { _id: 1 },
},
{
$project: {
_id: "$_id.day",
date: "$_id.day",
type: "$_id.type",
total: 1,
},
},
{
$group: {
_id: null,
stats: { $push: "$$ROOT" },
},
},
{
$project: {
stats: {
$map: {
input: ["2018-09-01", "2018-09-02", "2018-09-03", "2018-09-04", "2018-09-05", "2018-09-06"],
as: "date",
in: {
$let: {
vars: { dateIndex: { $indexOfArray: ["$stats._id", "$$date"] } },
in: {
$cond: {
if: { $ne: ["$$dateIndex", -1] },
then: { $arrayElemAt: ["$stats", "$$dateIndex"] },
else: { _id: "$$date", date: "$$date", total: 0,type: "download" },
},
},
},
},
},
},
},
},
{
$unwind: "$stats",
},
{
$replaceRoot: {
newRoot: "$stats",
},
},
])
but this solution adds only a single object by missing day, and I need an object per type, so any solution would be appreciated

Answer 1

You can simply do it with $facet
$facet helps to categorize the incoming data. So I get two arrays. One is match dates and another one is non match dates. In the match dates we need to add the condition
$concatArrays to join multiple arrays into one
$unwind to deconstruct the array
$replaceRoot to make it to root
Here is the code
db.collection.aggregate([
{
"$facet": {
"matchDate": [
{
$match: {
date: { $in: [ "2021-01-13","2021-04-21" ] }
}
},
{
$addFields: {
total: { $cond: [{ $eq: [ "$type", "demo" ]}, 0, "$total" ] }
}
}
],
"nonMatchDate": [
{
$match: {
date: { $nin: [ "2021-01-13", "2021-04-21" ] }
}
}
]
}
},
{
$project: {
combined: {
"$concatArrays": [ "$matchDate", "$nonMatchDate" ]
}
}
},
{ "$unwind": "$combined" },
{ "$replaceRoot": { "newRoot": "$combined" }}
])
Working Mongo playground