在 MongoDB 中复制键和值

本文介绍了在 MongoDB 中复制键和值的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

说明:我们如何复制字段 f1.我想引入名为f2的对象f1的副本，查看预期输出

Explanation: How we can make a duplication of the field f1. I want to introduce the replica of the object f1 that name as f2, see the expected output

{
    "data": [
        {
            "value": 100,
             "fl" :1
        },
        {
            "value": 300,
             "fl" :0
        },
        {
            "value": 14,
             "fl" :0
        },
        {
            "value": 3
             "fl" :0
        },
        {
            "value": 30,
             "fl" :1
        },
        {
            "value": 60,
             "fl" :1
        }
    ]
}

预期输出

{
   "data": [
       {
           "value": 100,
            "fl" :1,
            "f2" :1
       },
       {
           "value": 300,
            "fl" :0,
            "f2" :0
       },
       {
           "value": 14,
            "fl" :0,
            "f2" :0
       },
       {
           "value": 3,
            "fl" :0,
            "f2" :0
       },
       {
           "value": 30,
            "fl" :1,
            "f2" :1
       },
       {
           "value": 60,
            "fl" :1,
            "f2" :1,
       }
   ]
}

推荐答案

查询

和前面的无条件类似，阅读$map文档，你就可以做到这些

its similar with the previous here without condition, read $map documentation, you will be able to do all those

此处测试代码

db.collection.aggregate([
  {
    "$set": {
      "data": {
        "$map": {
          "input": "$data",
          "in": {
            "$mergeObjects": [
              "$$m",
              {
                "f2": "$$m.fl"
              }
            ]
          },
          "as": "m"
        }
      }
    }
  }
])

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