重命名（$project）数组中的字段 - MongoDB

Question

我有一个像下面这样的文件，

{
    "_id" : "59ba903dacea50d0d7d47168",
    "sections" : [ 
        {
            "_id" : "59d9dd7947ce651544c5d4c1",
            "sectionName" : "Section 1"
        }, 
        {
            "_id" : "59d9dd8147ce651544c5d4c2",
            "sectionName" : "Section 2"
        }, 
        {
            "_id" : "59d9dd9747ce651544c5d4c3",
            "sectionName" : "Section 3"
        }
    ]
}

我正在使用投影将字段 _id 重命名为 id 和 sectionName 以使用查询命名

db.getCollection('tmp').aggregate([
{$project:{"sections.id":"$sections._id", "sections.name":"$sections.sectionName"}}
])

所需的输出是：

{
    "_id": "59ba903dacea50d0d7d47168",
    "sections": [
        {"id": "59d9dd7947ce651544c5d4c1", "name": "Section 1"}, 
        {"id": "59d9dd8147ce651544c5d4c2", "name": "Section 2"}, 
        {"id": "59d9dd9747ce651544c5d4c3", "name": "Section 3"}
    ]
};

但它似乎不起作用，我做错了什么？

请注意，我并没有像在这个问题中那样尝试更新此文档，我想以所需的格式投影该文档。

Answer 1

如果我确实理解它，它应该通过$map运算符完成，如下所示：

db.getCollection('section').aggregate([
    {
        $project: {
           sections: {
               $map: {
                   "input": "$sections",
                   as: "sec",
                   in: {
                       "my_id": "$$sec._id",
                       "new_section_name": "$$sec.sectionName"
                   }
               }
           }
        }
    }
])

输出类似于以下内容：

{
  "waitedMS": NumberLong("0"),
  "result": [
    {
      "_id": "59ba903dacea50d0d7d47168",
      "sections": [
        {
          "my_id": "59d9dd7947ce651544c5d4c1",
          "new_section_name": "Section 1"
        },
        {
          "my_id": "59d9dd8147ce651544c5d4c2",
          "new_section_name": "Section 2"
        },
        {
          "my_id": "59d9dd9747ce651544c5d4c3",
          "new_section_name": "Section 3"
        }
      ]
    }
  ],
  "ok": 1
}