How to find distinct values of fields using facet operation in mongodb - mongodb

Question

The filteredAccording part and the categorizedBy is working as expected using the query which I provided in the link but I am facing issues in the findDistinct part.
In mongodb I have the following data:
{
"_id": 10001,
"university": "SPYU",
"Courses": [
"English",
"French"
],
"dept": [
"Literature"
],
"type": [
"Autonomous"
],
"status": "ACTIVE",
"isMarked": true
},
{
"_id": 10002,
"university": "SPYU",
"Courses": [
"English",
"French"
],
"dept": [
"Literature"
],
"type": [
"Autonomous"
],
"status": "NON-ACTIVE",
"isMarked": true
}
I wanted the response to be:
"university": [
{
"name": "Literature",
"values": [
{
"_id": 10001,
"university": "SPYU",
"Courses": [
"English",
"French"
],
"dept": [
"Literature"
],
"type": [
"Autonomous"
],
"status": "ACTIVE",
"isMarked": true
},
{
"_id": 10002,
"university": "SPYU",
"Courses": [
"English",
"French"
],
"dept": [
"Literature"
],
"type": [
"Autonomous"
],
"status": "NON-ACTIVE",
"isMarked": true
}
]
}
],
"findDistinct": [
{​​​​​​​​
"name": "Courses",
"values": [
"English",
"French"
]
}​​​​​​​​,
{​​​​​​​​
"name": "Status",
"values": [
"ACTIVE",
"NON-ACTIVE"
]
}​​​​​​​​
]
I tried it using this link but the response is not coming as expected.
https://mongoplayground.net/p/XECZvRMmt3T
Right now, the response is coming like this
"universities": [
{
"name": "Literature",
"values": [
{
"_id": 10001,
"university": "SPYU",
"Courses": [
"English",
"French"
],
"dept": [
"Literature"
],
"type": [
"Autonomous"
],
"status": "ACTIVE",
"isMarked": true
},
{
"_id": 10002,
"university": "SPYU",
"Courses": [
"English",
"French"
],
"dept": [
"Literature"
],
"type": [
"Autonomous"
],
"status": "NON-ACTIVE",
"isMarked": true
}
]
}
],
"findDistinct": [
{​​​​​​​​
"Courses": [
"English",
"French"
]
}​​​​​​​​,
{​​​​​​​​
"status": [
"ACTIVE",
"NON-ACTIVE"
]
}​​​​​​​​
]
Any Help will be appreciated!!

Answer 1

Quick fixes in your query,
universities:
$addFields, remove $project and add only one operation for isMarked
$unwind deconstruct dept array
$group by dept and get values array of root
findDistinct:
$group by null and get unique courses array and status
$reduce to iterate loop of Courses nested array and get unique array using $setUnion
Make array of course and status in dest field
$unwind deconstruct dest array
$replaceRoot replace dest object to root
db.collection.aggregate([
{ $match: { university: "SPYU" }
},
{
$facet: {
universities: [
{ $addFields: { isMarked: { $in: ["French", "$Courses"] } } },
{ $unwind: "$dept" },
{
$group: {
_id: "$dept",
values: { $push: "$$ROOT" }
}
}
],
findDistinct: [
{
$group: {
_id: null,
Courses: { $addToSet: "$Courses" },
Status: { $addToSet: "$status" }
}
},
{
$project: {
_id: 0,
dist: [
{
name: "Courses",
values: {
$reduce: {
input: "$Courses",
initialValue: [],
in: { $setUnion: ["$$this", "$$value"] }
}
}
},
{
name: "Status",
values: "$Status"
}
]
}
},
{ $unwind: "$dist" },
{ $replaceRoot: { newRoot: "$dist" } }
]
}
}
])
Playground