Populate to the deep level using $lookup mongodb - mongodb

Question

I am using $lookup to join two collections and get data from below query:
let condition = {status:{$ne:config.PROJECT_STATUS.completed}, assignId:mongoose.Types.ObjectId(req.params.id)};
Project.aggregate([
{
$match: condition
},
{
"$group":{
"_id": "$_id"
}
},
{
"$lookup": {
"from": "worksheets",
"let": { "projectId": "$_id" },
"pipeline": [
{ "$match": { "$expr": { "$eq": [ "$projectId", "$$projectId" ] }}},
{ "$group": {_id:"$projectId", totalHours:{"$sum": "$hours"}}},
{
"$lookup": {
"from": "projects",
"let": { "projectId": "$_id" },
"pipeline": [
{ "$match": { "$expr": { "$eq": [ "$_id", "$$projectId" ] }}},
{ "$project": { "projectName": 1,"upworkdId":1,"status":1,"developers":1,"hoursApproved":1 }}
],
"as": "project"
}
}
],
"as": "projects"
}
}
])
.then((data)=>{
res.json(data);
})
And above query is giving me below result:
[
{
"_id": "5c0a4083753a321c6c4ee024",
"projects": [
{
"_id": "5c0a4083753a321c6c4ee024",
"totalHours": 11,
"project": [
{
"_id": "5c0a4083753a321c6c4ee024",
"hoursApproved": 24,
"developers": [
"5c0a29c697e71a0d28b910a9"
],
"projectName": "fallbrook winery",
"status": "pending"
}
]
}
]
}
]
Now i want to populate the developers subfield inside the project Array. How can i modify the above code to get that.

Answer 1

You can use $lookup one more deep level with the developers array.
Something like this
Project.aggregate([
{ "$match": condition },
{ "$group": { "_id": "$_id" }},
{ "$lookup": {
"from": "worksheets",
"let": { "projectId": "$_id" },
"pipeline": [
{ "$match": { "$expr": { "$eq": ["$projectId", "$$projectId"] } } },
{ "$group": { "_id": "$projectId", "totalHours": { "$sum": "$hours" } }},
{ "$lookup": {
"from": "projects",
"let": { "projectId": "$_id" },
"pipeline": [
{ "$match": { "$expr": { "$eq": ["$_id", "$$projectId"] } } },
{ "$lookup": {
"from": "developers",
"let": { "developers": "$developers" },
"pipeline": [
{ "$match": { "$expr": { "$in": ["$_id", "$$developers"] } } },
],
"as": "developers"
}},
{ "$project": {
"projectName": 1, "upworkdId": 1, "status": 1, "developers": 1, "hoursApproved": 1
}}
],
"as": "project"
}}
],
"as": "projects"
}}
])