MongoDB lookup - using $lookup - mongodb

Question

so i have document for users with this structure in JSON format:
[
{
"_id": {
"$oid": "6369aeb83ce0f8168520f42f"
},
"fullname": "Jokona",
"password": "$2b$10$MUAe7XIc/xtJTGVh/y1DeuShCARbwxCSejUbHaqIPZfjekNrn0.Yy",
"NIK": "MT220047",
"status": "active",
"department": "Logistic",
"position": "Management Trainee",
"Group_Shift": "Non Shift",
"role": "admin",
"createdAt": 1667870392,
"updatedAt": 1668564835,
"__v": 0
},
{
"_id": {
"$oid": "6369b17b11e02557349d8de5"
},
"fullname": "Warana",
"password": "$2b$10$0xaqz5V8bar/osWmsCiofet5bY10.ORn8Vme3QC7Dh0HwLHwYOm3a",
"NIK": "17000691",
"status": "active",
"department": "Production",
"position": "Foreman",
"Group_Shift": "R1",
"role": "user",
"__v": 0,
"createdAt": 1667871099,
"updatedAt": 1668496775
},
]
it try to lookitup using mongodb $lookup to get the fullname by joining using the NIK as the foreignnkey,here is what i have try:
const dataAnaylitics = await Answer.aggregate([
// $match stage
{
$group: {
_id: {
username: "$username",
title: "$title",
date: "$date",
},
count: {
$sum: 1,
},
position: {
$first: "$position",
},
department: {
$first: "$department",
},
},
},
{
$lookup: {
from: "users",
localField: "username",
foreignField: "NIK",
as: "fullname",
pipeline: [{ $project: { fullname: 0 } }],
},
},
{
$group: {
_id: {
username: "$_id.username",
title: "$_id.title",
},
dates: {
$push: {
k: "$_id.date",
v: "$count",
},
},
position: {
$first: "$position",
},
department: {
$first: "$department",
},
},
},
{
$project: {
_id: 0,
username: "$_id.username",
title: "$_id.title",
position: 1,
department: 1,
dates: 1,
},
},
{
$replaceRoot: {
newRoot: {
$mergeObjects: [
"$$ROOT",
{
$arrayToObject: "$dates",
},
],
},
},
},
{
$unset: "dates",
},
]);
but the result doesnt returning the fullname field, is there is something wrong with my code? i seek for documentation and already follow the step

Answer 1

In your group stage, since you are grouping based on username, the resulting document will have _id.username as the field. Use this field as localField in your lookup.
{
$lookup: {
from: "users",
localField: "_id.username",
foreignField: "NIK",
as: "fullname",
pipeline: [{ $project: { fullname: 0 } }],
}

Answer 2

i have fix it, hope it will helps other..
const dataAnaylitics = await Answer.aggregate([
// $match stage
{
$group: {
_id: {
username: "$username",
title: "$title",
date: "$date",
},
count: {
$sum: 1,
},
position: {
$first: "$position",
},
department: {
$first: "$department",
},
},
},
{
$lookup: {
from: "users",
localField: "_id.username",
foreignField: "NIK",
as: "fullname",
pipeline: [{ $project: { _id: 0, fullname: 1 } }],
},
},
{
$group: {
_id: {
username: "$_id.username",
title: "$_id.title",
},
dates: {
$push: {
k: "$_id.date",
v: "$count",
},
},
position: {
$first: "$position",
},
department: {
$first: "$department",
},
fullname: {
$first: { $arrayElemAt: ["$fullname.fullname", 0] },
},
},
},
{
$project: {
_id: 0,
username: "$_id.username",
title: "$_id.title",
position: 1,
department: 1,
dates: 1,
fullname: 1,
},
},
{
$replaceRoot: {
newRoot: {
$mergeObjects: [
"$$ROOT",
{
$arrayToObject: "$dates",
},
],
},
},
},
{
$unset: "dates",
},
]);