Recursive Mongo Find - mongodb

Question

So I want to find the names of people who are the partners of the current person.
My data looks like this:
{
_id: objectId,
first_name: string,
last_name: string,
partners: [objectId]
}
I have tried this aggregate/lookup - but it returns incorrect results
module.exports.getUserPartners = function( user_id, callback ) {
const query = [
{
$unwind: "$partners"
},
{
$lookup: {
from: "people",
localField: "partners",
foreignField: "_id",
as: "people_partners"
}
},
{
$match: { "_id": user_id }
},
{
$project: {
first_name: 1,
last_name: 1
}
}
];
People.aggregate( query, callback );
}
If my data looks like this: (and I pass '123' as the user_id)
{
_id: '123',
first_name: "bob",
last_name: "smith",
partners: ['234','345']
},{
_id: '234',
first_name: "sally",
last_name: "smartypants",
partners: ['789']
},{
_id: '345',
first_name: "martin",
last_name: "tall",
partners: []
}
I get these results from the above aggregate lookup:
[{
_id: '123',
first_name: "bob",
last_name: "smith"
},{
_id: '123',
first_name: "bob",
last_name: "smith"
}]
when I EXPECT these results:
[{
_id: '234',
first_name: "sally",
last_name: "smartypants"
},{
_id: '345',
first_name: "martin",
last_name: "tall"
}]
*NOTE - I added the $unwind based on recommendation form docs and this article
https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/#unwind-example

Answer 1

Please check this aggregate query. look like its complex.
db.getCollection('people').aggregate([
{$match : { "_id" : "123"} },
{
$unwind:
{
path:"$partners",
preserveNullAndEmptyArrays: true
}
},
{
$lookup: {
from: "people",
localField: "partners",
foreignField: "_id",
as: "people_partners"
}
},
{
$unwind:
{
path:"$people_partners",
preserveNullAndEmptyArrays: false
}
},
{
$project: {
_id : '$people_partners._id',
first_name : '$people_partners.first_name',
last_name : '$people_partners.last_name',
}
}
])