我是MongoDB的新手，正在使用NodeJS代码。

我需要使用聚合函数来获取每本书的最新book_version。

这是我的数据库的外观：

[
  {
    "book_id": "ab12nld”,"book_version": "0”,"author": “Sam”,“name”: “Sample Book”,“comments”: “Done”
  },{
    "book_id": "ab12nld”,"book_version": "1","author": "Martin","name": "Sample Book",“comments”: “In Progress”
  },"book_version": "2","author": "Roy",“comments”: “To-Do”
  }
]
[
  {
    "book_id": "bcj123n”,"author": “Don”,“name”: “Another Book”,{
    "book_id": "bcj123n”,"author": "Ray","name": "Another Book","author": "Max",“comments”: “To-Do”
  }
]
[
  {
    "book_id": "k23d1d3”,"author": “Sunny”,“name”: “New Book”,{
    "book_id": "k23d1d3”,"author": "Archer","name": "New Book",“comments”: “In Progress”
  }
]
[
  {
    "book_id": "o902f3s”,"author": “Joy”,“name”: “nice Book”,{
    "book_id": "o902f3s”,"author": "James","name": "nice Book","book_version": "2”,"author": “Pam”,"book_version": "3","author": "Jonah",“comments”: “Completed”
  }
]

因此，我应该为每个book_version以及整个对象获取book_id的最大值：

{
    "book_id": "ab12nld”,“comments”: “To-Do”
  },“comments”: “Completed”
  }