use lookup and group different collection mongodb - mongodb

Question

Hello I have the following collections
const TransactionSchema = mongoose.Schema({
schedule: {
type: mongoose.Schema.ObjectId,
required: true,
ref: "Schedule"
},
uniqueCode: {
type: String,
required: true
},
created: {
type: Date,
default: Date.now
},
status: {
type: String,
required: false
},
})
const ScheduleSchema = mongoose.Schema({
start: {
type: Date,
required: true,
},
end: {
type: Date,
required: false,
},
location: {
type: mongoose.Schema.ObjectId,
required: true,
ref: "Location"
},
})
and I want to return how many times the schedule appear in transaction ( where the status is equal to 'Active') and group it based on its location Id and then lookup the location collection to show the name.
For example I have the following data.
transaction
[
{
"_id":"identifier",
"schedule":identifier1,
"uniqueCode":"312312312312",
"created":"Date",
"status": 'Active'
},
{
"_id":"identifier",
"schedule":identifier1,
"uniqueCode":"1213123123",
"created":"Date",
"status": "Deleted"
}
]
schedule
[
{
"_id":identifier1,
"start":"date",
"end":"date",
"location": id1
},
{
"_id":identifier2,
"start":"date",
"end":"date",
"location": id2
}
]
and I want to get the following result and limit the result by 10 and sort it based on its total value:
[
{
"locationName":id1 name,
"total":1
},
{
"locationName":id2 name,
"total":0
}
]
thank you. Sorry for my bad english.

Answer 1

A bit complex and long query.
$lookup - schedule collection joins with transaction collection by matching:
_id (schedule) with schedule (transaction)
status is Active
and return a transactions array.
$lookup - schedule collection joins with location collection to return location array.
$set - Take the first document in location array so this field would be a document field instead of an array. [This is needed to help further stage]
$group - Group by location._id. And need the fields such as location and total.
$sort - Sort by total DESC.
$limit - Limit to 10 documents to be returned.
$project - Decorate the output documents.
db.schedule.aggregate([
{
$lookup: {
from: "transaction",
let: {
scheduleId: "$_id"
},
pipeline: [
{
$match: {
$expr: {
$and: [
{
$eq: [
"$schedule",
"$$scheduleId"
]
},
{
$eq: [
"$status",
"Active"
]
}
]
}
}
}
],
as: "transactions"
}
},
{
$lookup: {
from: "location",
localField: "location",
foreignField: "_id",
as: "location"
}
},
{
$set: {
location: {
$first: "$location"
}
}
},
{
$group: {
_id: "$location._id",
location: {
$first: "$location"
},
total: {
$sum: {
$size: "$transactions"
}
}
}
},
{
$sort: {
"total": -1
}
},
{
$limit: 10
},
{
$project: {
_id: 0,
locationName: "$location.name",
total: 1
}
}
])
Sample Mongo Playground