MongoDB Aggregate two collections and flatten the second collection - mongodb

Question

Collection - 1 (users)
{
"_id" : "aandtv10#gmail.com",
"updateTimestamp" : "2022-07-19T11:59:18.029Z",
"userConsent" : null,
"firstName" : "Aand",
"lastName" : "Aa",
"fullName" : "Aand Aa",
"orgRootName" : "Black&Veatch",
"relationType" : "Contractor"
}
Collection -2 (2 documents)
/* 1 */
{
"_id" : ObjectId("62e9296bf06b3bfdc93be0da"),
"lastUpdated" : "2022-08-02T13:40:59.265Z",
"email" : "aandtv10#gmail.com",
"userName" : "Aand Aa",
"docType" : "dose2",
"administeredTimestamp" : "2022-10-02T11:10:55.784Z",
"uploadTimestamp" : "2022-08-02T13:40:59.265Z",
"manufacturer" : "Novavax"
}
/* 2 */
{
"_id" : ObjectId("62e911cf5b6e67c36c4f843e"),
"lastUpdated" : "2022-08-02T12:00:15.201Z",
"email" : "aandtv10#gmail.com",
"userName" : "Aand Aa",
"templateName" : "Covid-Vaccine",
"docType" : "dose1",
"exemptType" : null,
"administeredTimestamp" : "2022-08-23T17:16:20.347Z",
"uploadTimestamp" : "2022-08-02T12:00:15.202Z",
"manufacturer" : "Novavax"
}
Expected Result:
{
"_id" : "aandtv10#gmail.com",
"updateTimestamp" : "2022-07-19T11:59:18.029Z",
"firstName" : "Aand",
"lastName" : "Aa",
"fullName" : "Aand Aa",
"orgRootName" : "Black&Veatch",
"relationType" : "Contractor",
"dose1_administeredTimestamp" : "2022-08-23T17:16:20.347Z",
"dose1_manufacturer" : "Novavax",
"dose2_administeredTimestamp" : "2022-10-02T11:10:55.784Z",
"dose2_manufacturer" : "Novavax"
}
Query Used:
db.users.aggregate([{
"$match": {
"_id": "aandtv10#gmail.com"
}
},{
$lookup: {
from: "documents",
localField: "_id",
foreignField: "email",
as: "documents"
}}, { $unwind: "$documents" },{
"$group": {
"fullName": { $max: "$identity.fullName" },
"_id":"$_id",
"relationship": { $max:"$seedNetwork.relationType" },
"registration_date": { $max:"$seedNetwork.seededTimestamp" },
"vaccination_level": { $max: "" },
"exemption_declination_date": { $max:"N/A" },
"exemption_verification": { $max: "N/A" },
"dose1_date" : { $max: { $cond: { if: {$eq: ["$docType", "dose1" ]}, then: "$administeredTimestamp", else: "<false-case>" } } }
}
}
]);

Answer 1

One option is using $reduce with $arrayToObject:
db.users.aggregate([
{$match: {_id: "aandtv10#gmail.com"}},
{$set: {data: "$$ROOT"}},
{$lookup: {
from: "documents",
localField: "_id",
foreignField: "email",
as: "documents"
}
},
{$project: {
_id: 0,
data: 1,
documents: {
$reduce: {
input: "$documents",
initialValue: [],
in: {
$concatArrays: [
"$$value",
[
{k: {$concat: ["$$this.docType", "_administeredTimestamp"]},
v: "$$this.administeredTimestamp"},
{k: {$concat: ["$$this.docType", "_manufacturer"]},
v: "$$this.manufacturer"}
]
]
}
}
}
}
},
{$replaceRoot: {newRoot: {$mergeObjects: ["$data", {$arrayToObject: "$documents"}]}}}
])
See how it works on the playground example