Mongodb aggregation with referred collection - mongodb

Question

I want to get a list of my second level affiliate users, I've designed the collection like
user
{
"_id" : ObjectId("5a1b9df7bfdbfef2d4f1e9f3"),
"name" : "name 1",
"affKey" : "H1g-CfFxG",
}
{
"_id" : ObjectId("5a1bce5e9a2918f71a9ac4fb"),
"name" : "name 2",
"affKey" : "K1gKJfFxG",
}
affilites
{
"affKey" : "H1g-CfFxG",
"affUsers" : [
ObjectId("5a1bce5e9a2918f71a9ac4fb")
],
}
{
"affKey" : "K1gKJfFxG",
"affUsers" : [
ObjectId("5a1b9e43bfdbfef2d4f1e9f8"),
ObjectId("5a1b9e43bfdbfef2d4f1e911"),
],
}
Here I am saving a new set in affiliate.affKey is based on Users.affKey
Now I want to get a list of my first and second level affiliates, i.e. the list of affiliates of 5a1b9e43bfdbfef2d4f1e9f6 and 5a1bce5e9a2918f71a9ac4fb along with first level affiliate.
expecting the results like
{
first: [first level affiliates] // 1 result
second: [second level affiliates] // 2 results
}

Answer 1

For this situation you have to some steps to get expected result. can follow bellow steps
$lookup the affiliets collection for affKey
Then you have to $lookup the users collection to get the reference user information
After that you have to $lookup again the affiliets collection for second level user affKey
so query can be like bellow
db.users.aggregate([
{
$lookup: {
from: "affilites",
localField: "affKey",
foreignField: "affKey",
as: "affUsers"
}
},
{
$project: {
name: 1,
affKey: 1,
first: {$arrayElemAt: ["$affUsers.affUsers", 0]},
secondLevelUserId: {$arrayElemAt: ["$affUsers.affUsers", 0]}
}
},
{ $unwind: { path: "$secondLevelUserId", "preserveNullAndEmptyArrays": true }},
{
$lookup: {
from: "users",
localField: "secondLevelUserId",
foreignField: "_id",
as: "secondLevelUser"
}
},
{
$project: {
name: 1,
affKey: 1,
first: 1,
secondLevelUser: {$arrayElemAt: ["$secondLevelUser", 0]}
}
},
{
$lookup: {
from: "affilites",
localField: "secondLevelUser.affKey",
foreignField: "affKey",
as: "secondLevelUser"
}
},
{
$project: {
name: 1,
affKey: 1,
first: 1,
second: {$arrayElemAt: ["$secondLevelUser.affUsers", 0]}
}
},
{
$unwind: {
"path": "$second",
"preserveNullAndEmptyArrays": true
}
},
{
$group: {
_id: "$_id",
name: {$first: "$name"},
affKey: {$first: "$affKey"},
first: {$first: "$first"},
second: {$addToSet: "$second"}
}
}
]);
After execute the query you will get result like bellow
first document:
{
"_id" : ObjectId("5a1b9df7bfdbfef2d4f1e9f3"),
"name" : "name 1",
"affKey" : "H1g-CfFxG",
"first" : [
ObjectId("5a1bce5e9a2918f71a9ac4fb")
],
"second" : [
ObjectId("5a1b9e43bfdbfef2d4f1e911"),
ObjectId("5a1b9e43bfdbfef2d4f1e9f8")
]
}
second document
{
"_id" : ObjectId("5a1bce5e9a2918f71a9ac4fb"),
"name" : "name 2",
"affKey" : "K1gKJfFxG",
"first" : [
ObjectId("5a1b9e43bfdbfef2d4f1e9f8"),
ObjectId("5a1b9e43bfdbfef2d4f1e911")
],
"second" : []
}