Mongodb 查找平均值取决于值答案

【问题标题】：Mongodb Finding average of depends on the valueMongodb 查找平均值取决于值
【发布时间】：2021-09-10 10:58:43
【问题描述】：

这是我的收藏，其中包含课程单元列表和字段的信息，以表示单元是否已被阅读。

{
    "_id": "612f5605dc3813a3717663fe",
    "units": [
        {
            "unit": "612f5608dc3813268a766417",
            "alreadyRead": 1
        },
        {
            "unit": "612f5608dc38133ee6766411",
            "alreadyRead": 1
        },
        {
            "unit": "61322aa16c985ae927308a82",
            "alreadyRead": 1
        },
        {
            "unit": "612f560cdc38137394766440",
            "alreadyRead": 0
        },
        {
            "unit": "612f5614dc38139a927664b2",
            "alreadyRead": 0
        },
        {
            "unit": "612f5621dc381387d976653f",
            "alreadyRead": 0
        }
    ]
},
{
    "_id": "612f5622dc381383dd766545",
    "units": [
        {
            "unit": "612f5625dc3813e311766560",
            "alreadyRead": 1
        },
        {
            "unit": "612f5625dc381386bb76655a",
            "alreadyRead": 1
        },
        {
            "unit": "612f5626dc38132a2d766566",
            "alreadyRead": 1
        },
        {
            "unit": "612f5628dc3813a36d7665bd",
            "alreadyRead": 0
        },
        {
            "unit": "612f5626dc3813af32766574",
            "alreadyRead": 0
        },
    ]
},

我想要如下输出。只需要找到取决于alreadyRead 字段的平均值并将其放入avgCompleted。有没有办法做到这一点？

{
    "_id": "612f5605dc3813a3717663fe",
    "units": [
        {
            "unit": "612f5608dc3813268a766417",
            "alreadyRead": 1
        },
        {
            "unit": "612f5608dc38133ee6766411",
            "alreadyRead": 1
        },
        {
            "unit": "61322aa16c985ae927308a82",
            "alreadyRead": 1
        },
        {
            "unit": "612f560cdc38137394766440",
            "alreadyRead": 0
        },
        {
            "unit": "612f5614dc38139a927664b2",
            "alreadyRead": 0
        },
        {
            "unit": "612f5621dc381387d976653f",
            "alreadyRead": 0
        }
    ],
    "avgCompleted": 50
},
{
    "_id": "612f5622dc381383dd766545",
    "units": [
        {
            "unit": "612f5625dc3813e311766560",
            "alreadyRead": 1
        },
        {
            "unit": "612f5625dc381386bb76655a",
            "alreadyRead": 1
        },
        {
            "unit": "612f5626dc38132a2d766566",
            "alreadyRead": 1
        },
        {
            "unit": "612f5628dc3813a36d7665bd",
            "alreadyRead": 0
        },
        {
            "unit": "612f5626dc3813af32766574",
            "alreadyRead": 0
        },
    ],
    "avgCompleted": 60
},

【问题讨论】：

标签： mongodb aggregation-framework average

【解决方案1】：

你只需要使用$avg并乘以100就可以得到你想要的值。

使用$set 创建字段avgCompleted，其中值为100 * $avg。

db.collection.aggregate([
  {
    "$set": {
      "avgCompleted": {
        "$multiply": [
          100,
          {
            "$avg": "$units.alreadyRead"
          }
        ]
      }
    }
  }
])

例如here

【讨论】：