$lookup with conditional localField

[kevin_Morte_i_Piferrer (km)]

Very true Steevej,
I over supposed. I looked those links you send and I’m wondering if that could be the solution for another issue I have.
Could you check this?

Best way to insert document with id's from other recently created collections

Hi, I’m building a logic that basically uploads documents to one or several collection in MongoDb from an excel file. Sometimes, the own excel file insert new documents whose ID will be a paramater value from other documents. For example, one sheet contains customers and the next one invoices, so when the invoice is being sent, inserted to MongoDB, it shoud have the parameter customer changed from the string (the one used in the previouse sheet to insert the customer) to the ObjectId that the…

I think It can’t because that solution has to do with $lookup and I would need to perform with a bulk operation.