MongoDB $lookup - conditional value for localfield? - mongodb

Question

I have 2 collections I want to combine using lookup.
Collection1: _AddressSyncStatus
fields I wanna use from this collection: "address"
Collection2: EthTokenTransfers
Fields I want to use from this collection: "to_address", "from_address".
Now when I use mongo compass, the lookup filter expects a local field, in my case the local field of EthTokenTransfers to join the collections. My problem now is, that I want to lookup where address from _AddressSyncStatus is either EthTokenTransfers.from_address OR EthTokenTransfers.to_address.
Is this possible using aggregations?
{
from: '_AddressSyncStatus',
localField: 'string', //from_address OR to_address
foreignField: 'address',
as: 'synced_address'
}

Answer 1

One way to do it is using the $lookup pipeline with $or:
db.EthTokenTransfers.aggregate([
{
$lookup: {
from: "_AddressSyncStatus",
let: {
from_address: "$from_address",
to_address: "$to_address"
},
pipeline: [
{
$match: {
$expr: {$or: [{$eq: ["$_id", "$$from_address"]},
{$eq: ["$_id", "$$to_address"]}
]
}
}
}
],
as: "synced_address"
}
}
])
As you can see here.
But I think that for the rset of the work with this data, it will be more convenient like this:
db.EthTokenTransfers.aggregate([
{
$lookup: {
from: "_AddressSyncStatus",
localField: "from_address",
foreignField: "_id",
as: "synced_address_from"
}
},
{
$lookup: {
from: "_AddressSyncStatus",
localField: "to_address",
foreignField: "_id",
as: "synced_address_to"
}
}
])
As you can see here