Using document field as JS object field-name in aggregation pipeline - mongodb

Question

I have an JS object called tasksCountMap:
const tasksCountMap = {
'Freshman': 46,
'Senior': 10
}
and I need get count of task for each user type in my aggregation pipe, 'Freshman', 'Senior' it's document field called gradeLevel. I'm trying do it like this:
status: {
$let: {
vars: {
tasksCount: tasksCountMap['$gradeLevel'],
completedTasksCount: '$completedTasksCount[0].count'
},
in: {
$cond: {
if: { $or: [
{ $eq: ['$$tasksCount', '$$completedTasksCount'] },
{ $lte: ['$$tasksCount', '$$completedTasksCount'] },
]},
then: 'On track',
else: 'High priority'
}
}
}
}
Also '$completedTasksCount[0].count' doesn't work to...
Can someone show right way to do this?
All pipeline:
{
$match: {
type: 'student',
counselorUserName: username
},
$project: {
username: '$username',
email: '$email',
phone: '$phone',
fullName: '$fullName',
gradeLevel: {
$switch: {
branches: [{
case: {
$eq: ['$gradeLevel', '9']
},
then: 'Freshman'
},
{
case: {
$eq: ['$gradeLevel', '10']
},
then: 'Sophomore'
},
{
case: {
$eq: ['$gradeLevel', '11']
},
then: 'Junior'
},
{
case: {
$eq: ['$gradeLevel', '12']
},
then: 'Senior'
}
],
default: "Freshman"
}
}
},
$lookup: {
from: 'RoadmapTasksCompleted',
let: {
username: '$username',
gradeLevel: '$gradeLevel'
},
pipeline: [{
$match: {
monthToComplete: {
$in: prevMonthsNames
},
$expr: {
$and: [{
$eq: ['$username', '$$username']
},
{
$eq: ['$gradeLevel', '$$gradeLevel']
}
]
}
}
},
{
$count: 'count'
}
],
as: 'completedTasksCount'
},
$project: {
username: '$username',
email: '$email',
phone: '$phone',
fullName: '$fullName',
completedTask: { $arrayElemAt: ['$completedTasksCount', 0] },
status: {
$let: {
vars: {
tasksCount: tasksCountMap['$gradeLevel'],
completedTasksCount: '$completedTasksCount[0].count'
},
in: {
$cond: {
if: { $or: [
{ $eq: ['$$tasksCount', '$$completedTasksCount'] },
{ $lte: ['$$tasksCount', '$$completedTasksCount'] },
]},
then: '$$tasksCount',
else:'$$tasksCount'
}
}
}
}
}
$limit: 10,
$skip: 10,
}

Answer 1

You have to move the js map into the aggregation pipeline for you to be able to access the map.
I split $project stage into two and took the liberty to clean up the status calculation.
Something like
{"$project":{
"username":"$username",
"email":"$email",
"phone":"$phone",
"fullName":"$fullName",
"completedTask":{"$arrayElemAt":["$completedTasksCount",0]},
"tasksCountMap":[{"k":"Freshman","v":46},{"k":"Senior","v":10}]
}},
{"$addFields":{
"status":{
"$let":{
"vars":{
"tasksCount":{
"$arrayElemAt":[
"$tasksCountMap.v",
{"$indexOfArray":["$tasksCountMap.k","$gradeLevel"]}
]
},
"completedTasksCount":"$completedTask.count"
},
"in":{
"$cond":{
"if":{"$lte":["$$tasksCount","$$completedTasksCount"]},
"then":"$$tasksCount",
"else":"$$completedTasksCount"
}
}
}
}
}}