Mongodb - Get sales per hours - mongodb

Question

Good people! I am in need of your help.
I am trying to create a line graph using apexcharts with data imported from Mongodb.
I am trying to graph hourly sales, so I need the number of sales for each hour of the day.
Example Mongodb document.
{
"_id" : ObjectId("5dbee4eed6f04aaf191abc59"),
"seller_id" : "5aa1c2c35ef7a4e97b5e995a",
"temp" : "4.3",
"sale_type" : "coins",
"createdAt" : ISODate("2020-05-10T00:10:00.000Z"),
"updatedAt" : ISODate("2019-11-10T14:32:14.650Z")
}
Up to now I have a query like this:
db.getCollection('sales').aggregate([
{ "$facet": {
"00:00": [
{ "$match" : {createdAt: {$gte: ISODate("2020-05-10T00:00:00.000Z"),$lt: ISODate("2020-05-10T00:59:00.001Z")},seller_id: "5aa1c2c35ef7a4e97b5e995a",
}},
{ "$count": "sales" },
],
"01:00": [
{ "$match" : {createdAt: {$gte: ISODate("2020-05-10T01:00:00.000Z"),$lt: ISODate("2020-05-10T01:59:00.001Z")},seller_id: "5aa1c2c35ef7a4e97b5e995a",
}},
{ "$count": "sales" },
],
"02:00": [
{ "$match" : {createdAt: {$gte: ISODate("2020-05-10T02:00:00.000Z"),$lt: ISODate("2020-05-10T02:59:00.001Z")},seller_id: "5aa1c2c35ef7a4e97b5e995a",
}},
{ "$count": "sales" },
],
"03:00": [
{ "$match" : {createdAt: {$gte: ISODate("2020-05-10T03:00:00.000Z"),$lt: ISODate("2020-05-10T03:59:00.001Z")},seller_id: "5aa1c2c35ef7a4e97b5e995a",
}},
{ "$count": "sales" },
],
}},
{ "$project": {
"ventas0": { "$arrayElemAt": ["$01:00.sales", 0] },
"ventas1": { "$arrayElemAt": ["$02:00.sales", 0] },
"ventas3": { "$arrayElemAt": ["$03:00.sales", 0] },
}}
])
But I am sure there is a more efficient way to do this.
My expected output looks like this:
[countsale(00:00),countsale(01:00),countsale(02:00),countsale(03:00), etc to 24 hs]

Answer 1

You are correct, there is a more efficient way to do this. We can use Date expression operators and specifically by grouping with $hour.
db.getCollection('sales').aggregate([
{
$match: {
createdAt: {$gte: ISODate("2020-05-10T00:00:00.000Z"), $lt: ISODate("2020-05-11T00:00:00.001Z")}
}
},
{
$group: {
_id: {$hour: "$createdAt"},
count: {$sum: 1}
}
},
{
$sort: {
_id: 1
}
}
]);
This will give you this result:
[
{
_id: 0,
count: x
},
{
_id: 1,
count: y
},
...
{
_id: 23,
count: z
}
]
From here you can restructure the data easily as you wish.
A problem I forsee happening are hours without any matches (i.e count=0) will not exists in the result set. you'll have to fill in those gaps manually.