MongoDB Online Test

You're working on a MongoDB database for a video game where players can sell their items, such as planks, to other players.

The Mongo Shell code to trade planks between players is the following:

// The seller and buyer variables were set to the ids of the seller and the buyer, respectively
// They both exist in the database
sellerPlayer = db.Players.findOne({ _id: seller });
buyerPlayer = db.Players.findOne({ _id: buyer });
if (sellerPlayer.planks >= 100 && buyerPlayer.gold >= 350) {
    db.Players.updateOne({ _id: seller }, { $inc: { gold: 350, planks: -100 }});
    db.Players.updateOne({ _id: buyer }, { $inc: { planks: 100, gold: -350 }});
}

What can be said about the code above in cases with no disconnections from the server?

You work for a mail delivery company and the tracker system uses MongoDB with the following document schema for the "Packages" collection:

{
  "_id": { "bsonType": "objectId" },
  "destination": { "bsonType": "string" },
  "state": { "enum": ["preparing", "in transit", "delivered"] }
}

Select all the correct statements about the Packages collection.