给定结果后，您可以直接根据结果创建新对象。

const res = await BusDayWise.findOne(
    { ...filter },
    { session: mongoSession }
  );

const result = [
    {
      "_id": res._id,
      "busNo": res.busNo,
      "city": res.city,
      "agency": res/agency,
      "date": res.date,
    }
],
const aggregates = 
{
    "ticketPrice": res.ticketPrice,
    "totalCollection": res.totalCollection,
    "helper": res.helper,
    "driver": res.driver,
}

更高级的答案

您可以拥有一个仅从词典中检索特定关键字函数

function subDict(dict, keys){
   const newDict = {};
   keys.forEach(key => newDict[key] = dict[key]);
   return newDict 
}

test = {"a": 1, "b": 2, "c": 3}
keys = ["a", "c"];
newTest = subDict(test, keys); // {"a": 1; "c": 3}

所以在你的情况下

const result = subDict(res, ["_id", "busNo", "city","agency", "date"]);
const aggregates = subDict(res, ["ticketPrice", "totalCollection", "helper", "driver"]);

这应该与投影非常简单，投影是改变文档形状的行为。
您编辑的问题现在包括对最简单投影类型的引用，但不包括there are many more。在您的情况下，看起来您仍然可以使用相对简单的一个，试试这个：

{
  "result._id": "$_id",
  "result.busNo": "$busNo",
  "result.city": "$city",
  "result.agency": "$agency",
  "result.date": "$date",
  "aggregates.ticketPrice": "$ticketPrice",
  "aggregates.totalCollection": "$totalCollection",
  "aggregates.helper": "$helper",
  "aggregates.driver": "$driver",
  _id: 0
}

Playground demonstration here.
如果每次检索数据时都要这样做，那么您可能希望更改文档的模式，因为它们存储在数据库中。或者，您可以使用create a view来定义该投影，然后在每次查询数据时自动应用该投影，而不必依赖于客户端来请求数据。