MongoDB reduce nested - json

Question

I have a collection of a class that looks something like that:
[
{
"_id": 1,
"title": "dummy title",
"assignments": [
{
"_id": 1,
"name": "a1",
"members": [
{
"_id": 11,
"full_name": "john doe",
"aga": 18
},
{
"_id": 12,
"full_name": "john doe2",
"aga": 18
}
]
}
],
"settings": [
{
"type": "light",
"status": "enabled"
},
{
"type": "flare",
"status": "disabled"
},
{
"type": "toolbar",
"status": "enabled"
}
]
}
]
I have 2 nested documents here "assignments" which have a nested "members"
and "settings". the result i want should look something like that:
{
"_id": 1,
"title": "dummy title",
"assignments": [
{
"_id": 1,
"name": "a1",
"member_ids": [11, 18]
}
],
"active_settings": ["light", "toolbar"]
}
Meaning in each "assignment" I should only return the ids of the members and not the whole member data. and in settings I should only return the settings that are set to "active"
is it possible?
Playground here:
https://mongoplayground.net/p/Le4BdTm_gOv

Answer 1

You can try with $map to go one by one. $mergeObjects helps to merge the output value with same object
[
{
$project: {
title: 1,
assignments: {
$map: {
input: "$assignments",
in: {
$mergeObjects: [
"$$this",
{
members: {
$map: {
input: "$$this.members",
in: "$$this._id"
}
}
}
]
}
}
},
active_settings: {
$reduce: {
input: "$settings",
initialValue: [],
in: {
$cond: [
{
$eq: [
"$$this.status",
"enabled"
]
},
{
$setUnion: [
"$$value",
[
"$$this.type"
]
]
},
"$$value"
]
}
}
}
}
}
]
Working Mongo playground

Answer 2

You can try,
get assignments member ids using $map and $reduce
get active_settings using $reduce
db.collection.aggregate([
{
$project: {
_id: 1,
title: 1,
assignments: {
$map: {
input: "$assignments",
in: {
_id: "$$this._id",
name: "$$this.name",
memberIds: {
$reduce: {
input: "$$this.members",
initialValue: [],
in: { $concatArrays: ["$$value", ["$$this._id"]] }
}
}
}
}
},
active_settings: {
$reduce: {
input: "$settings",
initialValue: [],
in: {
$cond: [
{ $eq: ["$$this.status", "enabled"] },
{ $concatArrays: ["$$value", ["$$this.type"]] },
"$$value"
]
}
}
}
}
}
])
Playground