How to do a Mongodb $lookup for local and foreign array fields - mongodb

Question

Trying to do $lookup s for local array fields which is inside an object.
Querying case collection :
{
"no" : "2020921008981",
"sale" : {
"soldItems" : [
{
"itemId" : "5b55ac7f0550de00210a3b24",
},
{
"itemId" : "5b55ac7f0550de00215584re",
}
],
"bills" : [
{
"billNo" : "2020921053467",
"insurancePlanId" : "160",
},
{
"billNo" : "2020921053467",
"insurancePlanId" : "170",
}
]
}
}
Item collection :
{
"_id" : ObjectId("5b55ac7f0550de00210a3b24"),
"code" : "ABCDE"
},
{
"_id" : ObjectId("5b55ac7f0550de00215584re"),
"code" : "PQRST"
}
Insurance collection :
{
"_id" : ObjectId("5b55aca20550de00210a6d25"),
"name" : "HIJKL"
"plans" : [
{
"_id" : "160",
"name" : "UVWZ",
},
{
"_id" : "161",
"name" : "LMNO",
}
]
},
{
"_id" : ObjectId("5b55aca20550de00210a6d25"),
"name" : "WXYZ"
"coveragePlans" : [
{
"_id" : "169",
"name" : "5ABC",
},
{
"_id" : "170",
"name" : "4XYZ",
}
]
}
Desired output :
{
"no" : "2020921008981",
"sale" : {}
"insurances" : "HIJKL \n WXYZ",
"items" : [
{
"_id" : ObjectId("5b55ac7f0550de00210a3b24"),
"code" : "ABCDE"
},
{
"_id" : ObjectId("5b55ac7f0550de00215584re"),
"code" : "PQRST"
}
]
}
The attempt to lookup using the local itemRefId field from the item collection. And to lookup using the local insurancePlanId from the insurance collection and then $reduce the returning array into the desired format for the insurances field:
{
$lookup:
{
from: "item",
let: { iid: "$sale.soldItems.itemId" },
pipeline: [
{
$match: {
$expr: {
$in: ["$_id", {
$map: {
input: "$$iid",
in: { $_id: "$$this" }
}
}
]
}
}
}
],
as: "items"
}
},
{
$lookup:
{
from: "insurance",
let: { iid: "$sale.insurances.insurancePlanId" },
pipeline: [
{
$match: {
$expr: {
$in: ["$insurance.plans._id", {
$map: {
input: "$$iid",
in: { $toObjectId: "$$this" }
}
}
]
}
}
}
],
as: "insurancesList"
}
},
{
$addFields: {
insurances: {
$reduce: {
input: "$insurancesList.name",
initialValue: "",
in: {
$cond: [ { "$eq": [ "$$value", "" ] }, "$$this", { $concat: [ "$$value", "\n", "$$this" ] } ]
}
}
}
}
}
This attempt returns a mongodb error. Any help to get the desired output would be appreciated.

Answer 1

db.case.aggregate([
{
$lookup: {
from: "insurance",
let: { ipids: "$salesOrder.invoices.insurancePlanId" },
pipeline: [
{
$unwind: "$coveragePlans"
},
{
$match: { $expr: { $in: ["$coveragePlans._id", "$$ipids"] } }
},
{
$project: { _id: 0, name: 1 }
}
],
as: "insurances"
}
},
{
$lookup: {
from: "item",
let: { iid: "$salesOrder.purchaseItems.itemRefId" },
pipeline: [
{
$match: {
$expr: {
$in: ["$_id", {
$map: {
input: "$$iid",
in: { $toObjectId: "$$this" }
}
}
]
}
}
}
],
as: "items"
}
},
{
$project: {
_id: 0,
caseNumber: 1,
insurances: {
$reduce: {
input: "$insurances",
initialValue: "",
in: { $concat: ["$$value", "$$this.name", " \n "] }
}
},
items: 1
}
}
])