MongoDB 聚合：计算数组中的不同字段

Question

需要使用JS在mongodb查询中计算所有寄存器上的不同标签。

寄存器结构：

  {
  "_id": {
    "$oid": "62e593aed8fd9808777225e8"
  },
  "title": "“The world as we have created it is a process of our thinking. It cannot be changed without changing our thinking.”",
  "author": {
    "name": "Albert Einstein",
    "url": "https://quotes.toscrape.com/author/Albert-Einstein"
  },
  "tag": [
    "change",
    "deep-thoughts",
    "thinking",
    "world"
  ]
  }

Answer 1

这可能很有用。 除了获取字段的不同值外，它还返回出现次数：

db.collection.aggregate([
  {
    "$unwind": "$tag"
  },
  {
    "$group": {
      "_id": "$tag",
      "total": {
        "$sum": 1
      }
    }
  },
  
])

你可以在这里试试： https://mongoplayground.net/p/yXLYkJKO3Wf