Can I generate unique String _ids in aggregation pipeline

Question

I am planning on transforming a large data set from my mongo database and creating a new collection from the transformed documents. I wanted to do this as part of a single aggregation to stop round trips back and forth from the server and the database. Our application automatically enforces String type ID's, so I cannot use the automatic _ids generated by $out / $merge as these are ObjectIds()

Obviously I can pull the data down and generate a unique string ID for each document then insert them but I was hoping for a way to do this within a single aggregation query. Any ideas?

Answer 1

Take a look here how to $project ObjectId to string value in mongodb aggregate?

We do pretty much the same thing in our mongo scripts:

db.YourCollection.insert({
    _id: new ObjectId().valueOf(),
    ...fields
});