mongodb - 克隆并重命名 Mongodb 中子文档数组的字段

Question

我有一个这样的集合:

{
  name: "A Name",
  answers: [
    {order: 1},
    {order: 2}, 
    {order: 3}
  ]
}

我想要做的是添加一个新的文件 id到 answers 的每个元素基于 order 的值的数组属性 - 我只想克隆它，所以输出是

{
  name: "A Name",
  answers: [
    {order: 1, id: 1},
    {order: 2, id: 2}, 
    {order: 3, id: 3}
  ]
}

我看了 this post和 this one也是，但我不知道如何将它们组合起来才能正常用于子文档。
在 aggregate 的 MongoDB 文档中方法，我找到了一个如何更新嵌入文档的简单示例 here ，但我不知道如何使用 order属性(property)而不是固定期限。以下尝试似乎无法按我的需要工作:

db.collection.aggregate([
  {
    $addFields: {
      "answers.id": "answers.$.order" 
    }
  }
])

db.collection.aggregate([
  {
    $addFields: {
      "answers.id": "$answers.order" 
    }
  }
])

使用`aggregate 方法是否可以达到预期的结果？

Answer 1

演示 - https://mongoplayground.net/p/M79MV6-Zp4C

db.collection.aggregate([
  {
    $set: {
      answers: {
        $map: {
          input: "$answers",
          as: "answer",
          in: {  $mergeObjects: [ "$$answer", { id: "$$answer.order" } ]
          }
        }
      }
    }
  }
])

更新演示 - https://mongoplayground.net/p/iyqIPGQ5-ld

db.collection.aggregate([
  {  $unwind: "$answers" },
  {
    $group: {
      _id: "$_id",
      answers: { $push: { order: "$answers.order", id: "$answers.order" } },
      name: { $first: "$name" } // preserve properties add them to the group pick 1st value
    }
  }
])

演示 - https://mongoplayground.net/p/Ln5CcmT-Kkm

db.collection.aggregate([
  { $unwind: "$answers" }, // break into individuals documents
  { $addFields: { "answers.id": "$answers.order" } }, // copy order value to id
  { $group: { _id: "$_id", answers: { $push: "$answers" } } } // join and group it back
])

如果你想排序 n 从索引中获取 id
演示 - https://mongoplayground.net/p/6U_sRYWHtDR

db.collection.aggregate([
  { $sort: { "answers.order": 1 } },
  { $unwind: { path: "$answers", includeArrayIndex: "index" } },
  { $group: { _id: "$_id", answers: { "$push": {  order: "$answers.order", id: { $add: [ "$index", 1 ] } } } } }
])