Get data from two collection with specific data Mongo - sql

Question

Get data from two collection from first collection(test1) all data and from second collection (test2) customer name using createdBy and updatedBy from test1 collection.
In createdBy and updatedBy I want fullname from test2 collection:
Test1 collection:
{
"_id": "kcXtyaB7jGPw9Ks",
"dateCreated": "2022-07-12T13:09:16.270Z",
"dateModified": "2022-07-12T13:09:16.270Z",
"data1": 1,
"data2": 100,
"data3": 5,
"createdBy": "xQQrzRgi8",
"updatedBy": "56sgAeKfx"
}
Test2 collection:
{
"_id": "xQQrzRgi8",
"fullName": "test name created"
},
{
"_id": "56sgAeKfx",
"fullName": "test name update"
}
Response be like:
{
"_id": "kcXtyaB7jGPw9Ks",
"dateCreated": "2022-07-12T13:09:16.270Z",
"dateModified": "2022-07-12T13:09:16.270Z",
"data1": 1,
"data2": 100,
"data3": 5,
"createdBy": "test name created",
"updatedBy": "test name update"
}

Answer 1

If I've understood correctly, you can use $lookup like this:
This query do a "join" between "Test1" and "Test2" using updatedBy and _id fields.
And after that get the first element in the result (I assume there were only one element because you are comparing with _id but if there is more than one you can use another way like $unwind) to output the value.
Edit: To get both values (created and updated) you can do a second $lookup.
Now the query:
Get the updatedBy name from field _id in Test2.
Set value into field updatedBy.
Get the createdBy name from field _id in Test2.
Set value into field createdBy.
Use $project to not output result.
db.Test1.aggregate([
{
"$lookup": {
"from": "Test2",
"localField": "updatedBy",
"foreignField": "_id",
"as": "result"
}
},
{
"$set": {
"updatedBy": {
"$first": "$result.fullName"
}
}
},
{
"$lookup": {
"from": "Test2",
"localField": "createdBy",
"foreignField": "_id",
"as": "result"
}
},
{
"$set": {
"createdBy": {
"$first": "$result.fullName"
}
}
},
{
"$project": {
"result": 0
}
}
])
Example here

Answer 2

I solved my query with below mongo query:
db.Test1.aggregate([
{
$lookup: {
from: "Test2",
localField: "updatedBy",
foreignField: "_id",
as: "updatedByName",
},
},
{
$lookup: {
from: "Test2",
localField: "createdBy",
foreignField: "_id",
as: "createdByName",
},
},
{
$set: {
updatedBy: {
$first: "$updatedByName.fullName",
},
},
},
{
$set: {
createdBy: {
$first: "$createdByName.fullName",
},
},
},
{
$project: {
updatedByName: 0,
createdByName: 0,
},
}
])
Here is Solved query https://mongoplayground.net/p/7Ekh-q8tkTy