MongoDb:如何将现有文档转换为预期的结构？

{
  "_id": 1,
  "name": "John",
  "age": 30
}

{
  "_id": 1,
  "fullName": "John",
  "age": 30
}

db.myCollection.updateOne(
  { "_id": 1 },
  {
    $set: {
      "fullName": "$name"
    }
  }
);

db.myCollection.updateMany(
  {},
  {
    $rename: {
      "name": "fullName"
    }
  }
);

{
  "_id": 1,
  "fullName": "John",
  "age": 30,
  "isAdult": true
}

db.myCollection.aggregate([
  {
    $addFields: {
      "fullName": "$name",
      "isAdult": { $gte: ["$age", 18] }
    }
  },
  {
    $project: {
      "name": 0
    }
  }
]).forEach(function(doc) {
  db.myCollection.replaceOne({ "_id": doc._id }, doc);
});