mongodb - How to sort by distance using geoNear in addition to looking up another collection - mongodb

Question

I have two functionalities working individually but want to combine them.
Functionality 1 - Sort users by their geoNear distance.
Functionality 2 - The users should not have already been liked by the
current user (look up partnership collection)
How to update this query to start from the user's collection so I can do geoNear?
The output in the below mongoplayground is correct except that the resulting users are not sorted by calculatedDist which is a field calculated by geoNear.
$geoNear: {
near: { type: "Point", coordinates: [x,y },
distanceField: "calculatedDist",
spherical: true
}
geoNear needs location which is only available in users collection hence I think below query needs to be modified to start in user's collection.
https://mongoplayground.net/p/7H_NxciKezB
db={
users: [
{
_id: "abc",
name: "abc",
group: 1,
location: {
type: "Point",
coordinates: [
54.23,
67.12
]
},
calculatedDist: 13
},
{
_id: "xyz",
name: "xyyy",
group: 1,
location: {
type: "Point",
coordinates: [
54.23,
67.12
]
},
calculatedDist: 11
},
{
_id: "123",
name: "yyy",
group: 1,
location: {
type: "Point",
coordinates: [
54.23,
67.12
]
},
calculatedDist: 2
},
{
_id: "rrr",
name: "tttt",
group: 1,
location: {
type: "Point",
coordinates: [
54.23,
67.12
]
},
calculatedDist: 11
},
{
_id: "eee",
name: "uuu",
group: 1,
location: {
type: "Point",
coordinates: [
54.23,
67.12
]
},
calculatedDist: 7
},
],
partnership: [
{
_id: "abc_123",
fromUser: "abc",
toUser: "123"
},
{
_id: "eee_rrr",
fromUser: "eee",
toUser: "rrr"
},
{
_id: "rrr_abc",
fromUser: "rrr",
toUser: "abc"
},
{
_id: "abc_rrr",
fromUser: "abc",
toUser: "rrr"
},
{
_id: "xyz_rrr",
fromUser: "xyz",
toUser: "rrr"
},
{
_id: "rrr_eee",
fromUser: "rrr",
toUser: "eee"
},
]
}
geoNear as far as I know has to be the first thing to be done so my query should start with the users collection. This breaks my partnership check because for that to work, I start at partnership collection.
In the playground above, the user eee has a lesser calculated distance as a result of geoNear but it shows after user abc.

Answer 1

Try this out:
db.partnership.aggregate([
// $geoNear
{
$match: {
$or: [
{
fromUser: "rrr"
},
{
toUser: "rrr"
}
]
}
},
{
$group: {
_id: 0,
from: {
$addToSet: "$fromUser"
},
to: {
$addToSet: "$toUser"
}
}
},
{
$project: {
_id: 0,
users: {
$filter: {
input: {
$setIntersection: [
"$from",
"$to"
]
},
cond: {
$ne: [
"$$this",
"rrr"
]
}
}
}
}
},
{
$lookup: {
from: "users",
let: {
userId: "$users"
},
pipeline: [
{
"$geoNear": {
"near": {
"type": "Point",
"coordinates": [
31.4998,
-61.4065
]
},
"distanceField": "calculatedDist",
"spherical": true
}
},
{
"$match": {
"$expr": {
"$in": [
"$_id",
"$$userId"
]
}
}
}
],
as: "users"
}
},
{
$project: {
users: 1,
count: {
$size: "$users"
}
}
}
])
Here, we use the pipelined form of lookup.
The lookup is on the user's collection, in which we specify a pipeline with the $geoNear stage as the first stage.
And finally filter out and only keep the users belonging to a partnership.
This is the playground link. Let me know if it works, on the playground I can't test it because $geoNear requires a 2d index.
While using calculatedDist, it looks like this:
db.partnership.aggregate([
// $geoNear
{
$match: {
$or: [
{
fromUser: "rrr"
},
{
toUser: "rrr"
}
]
}
},
{
$group: {
_id: 0,
from: {
$addToSet: "$fromUser"
},
to: {
$addToSet: "$toUser"
}
}
},
{
$project: {
_id: 0,
users: {
$filter: {
input: {
$setIntersection: [
"$from",
"$to"
]
},
cond: {
$ne: [
"$$this",
"rrr"
]
}
}
}
}
},
{
$lookup: {
from: "users",
let: {
userId: "$users"
},
pipeline: [
{
$sort: {
calculatedDist: 1
}
},
{
"$match": {
"$expr": {
"$in": [
"$_id",
"$$userId"
]
}
}
}
],
as: "users"
}
},
{
$project: {
users: 1,
count: {
$size: "$users"
}
}
}
])
Playground.