Mongodb aggregate to return result only if the lookup field has length - mongodb

Question

I have two collections users and profiles. I am implementing a search with the following query:
User.aggregate(
[
{
$match: {
_id: { $ne: req.user.id },
isDogSitter: { $eq: true },
profileId: { $exists: true }
}},
{
$project: {
firstName: 1,
lastName: 1,
email: 1,
isDogSitter: 1,
profileId: 1,
}},
{
$lookup: {
from: "profiles",
pipeline: [
{
$project: {
__v: 0,
availableDays: 0,
}},
{
$match: {
city: search
}}
],
as: "profileId",
}}
],
(error, result) => {
console.log("RESULT ", result);
}
);
What this does is that its searches for the city in the profiles collection and when there is not search match then profileId becomes an empty array. What I really want is that if the profileId is an empty array then I don't want to return the other fields in the documents too. It should empty the array. Below is my current returned result.
RESULT [
{
_id: 60cabe38e26d8b3e50a9db21,
isDogSitter: true,
firstName: 'Test',
lastName: 'Sitter',
email: 'test#user.com',
profileId: []
}
]

Answer 1

Add $match pipeline stage after the $lookup pipeline stage and
add the empty array condition check over there.
User.aggregate(
[
{
$match: {
_id: { $ne: req.user.id },
isDogSitter: { $eq: true },
profileId: { $exists: true }
}},
{
$project: {
firstName: 1,
lastName: 1,
email: 1,
isDogSitter: 1,
profileId: 1,
}},
{
$lookup: {
from: "profiles",
pipeline: [
{
$project: {
__v: 0,
availableDays: 0,
}},
{
$match: {
city: search
}}
],
as: "profileId",
}}
{
$match: { // <-- Newly added $match condition
"profileId": {"$ne": []}
},
},
],
(error, result) => {
console.log("RESULT ", result);
}
);