MongoDB Lookup MainField to FieldA or FieldB - mongodb

Question

I need to join two MongoDB Colletions with lookup, the MainField to join from de first collection has to join with the other collection through Field A or Field B.
MainField is an array, with this structure [Doc1.FieldA, Doc2.FieldA, Doc3.FieldB,...].
FieldA is Unique-Index.
FieldB is Non-Unique-Index, it is for group FieldB with a unique value.
The problem is that I need to keep the order of the MainField Array.
I like to do something like this:
db.getCollection("collection1").aggregate([
$lookup: {
from: "collection2",
localField: "mainField",
foreignField: $or:["fieldA","FieldB"]
as: "mainFieldInfo"
}]
Is it possible to do this lookup or I need a different approach?
Collections examples, the documents are simplified there are more fields
in each document.
Collection Machines (1 example) :
{
"_id" : ObjectId("5c793a188021710636865c33"),
"MachineName" : "CER3A",
"NextJobs" : [ //--> MainField
"ST105862", // match with FIELD B - Flags.STS
"OFT083520", // match with FIELD A - Lote
"OFT083365",
"ST105946"
]
}
Collection Works (2 example, 1 to match with FieldA, 1 to match Field B):
Field A example:
FieldB*(Flags.STS)* is empty
{
"_id" : ObjectId("5c1b89d0b6e97d001816595e"),
"Lote" : "OFT083520", //--> FIELD A
"Flags" : {
"ShipsFinished" : true,
"PlanFinished" : true,
"Finished" : true,
"IdDefecto" : false,
"EstadoOF" : 4,
"GCT" : "GCT018929",
"PedidoVenta" : "",
"STS" : "", //--> FIELD B
}
}
Field B Example (2 docs):
FieldA*(Lote)* is diferent in each document, FieldB*(Flags.STS)* is equal
{
"_id" : ObjectId("5dcd78e2a2061070185400e2"),
"Lote" : "OFT083671", //--> FIELD A
"Flags" : {
"B2" : 1,
"EstadoOF" : 4,
"Finished" : false,
"GCT" : "GCT024270",
"LaSI" : 0,
"PedidoVenta" : "P056048",
"SPO" : "PO23579",
"STS" : "ST105862", //--> FIELD B
"Inks" : "true",
}
}
{
"_id" : ObjectId("5dcd78e2a2061070185401f0"),
"Lote" : "OFT083672", //--> FIELD A
"Flags" : {
"B2" : 1,
"EstadoOF" : 4,
"Finished" : false,
"STS" : "ST105862", //--> FIELD B
"ShipsFinished" : false,
"TipoOF" : 1,
"EstatIQC" : 1,
}
}

Answer 1

You have to use the other form of $lookup stage, which allow to perform multiple conditions for the lookup stage.
Here's the query you have to run :
db.machines.aggregate([
{
$lookup: {
from: "works",
let: {
"nj": "$NextJobs"
},
pipeline: [
{
$match: {
$expr: {
$or: [
{
$in: [
"$Lote",
"$$nj"
]
},
{
$in: [
"$Flags.STS",
"$$nj"
]
}
]
}
}
}
],
as: "linkedWorks"
}
}
])
You can test it here