如何从 mongodb 集合的查询中获取计数？答案

【问题标题】：How to fetch counts from a query from a mongodb collection?如何从 mongodb 集合的查询中获取计数？
【发布时间】：2021-04-24 11:44:45
【问题描述】：

我想创建一种过滤体验，我从请求参数中获取过滤条件，并使用 mongo 聚合框架 过滤数据。请建议我一个合适的方法。

让数据的集合像

        {
            "material": "silver",
            "type": "beads",
            "shape": "round",
            "_user": "5f9b78bf1130ca88e2e1d"
        },
        {
            "material": "mixed",
            "type": "jewels",
            "shape": "round",
            "_user": "5f9b78bf1130ca88e2e1d"
        },
        {
            "material": "gold",
            "type": "jewels",
            "shape": "other",
            "_user": "5fda2b717112437f9c06"
        },
        {
            "material": "silver",
            "type": "jewels",
            "shape": "other",
            "_user": "5f9b78bf1130ca88e2e1d"
        },
        {
            "material": "mixed",
            "type": "jewels",
            "shape": "other",
            "_user": "5fda2b717112437f9c706"
        },

让查询的数据为 _user 等于 5f9b78bf1130ca88e2e1d， material 等于 silver, mixed 的数组， type 等于 珠子、珠宝 的数组 & shape 等于 round

的数组

我的查询应该返回每个过滤器类别（用户、材料、形状、类型）中的后续计数。

data = {
  categorizedByUser: [
    {
      _id: '5f9b78bf1130ca88e2e1d',
      count: 2
    },
    {
      _id: '5fda2b717112437f9c06',
      count: 0
    },
  ],
  categorizedByMaterial: [
    {
      _id: 'silver',
      count: 1
    },
    {
      _id: 'mixed',
      count: 1
    },
    {
      _id: 'gold',
      count: 0
    },
  ],
  categorizedByShape: [
    {
      _id: 'round',
      count: 2
    },
    {
      _id: 'other',
      count: 0
    },
  ]
  categorizedByType: [
    {
      _id: 'beads',
      count: 1
    },
    {
      _id: 'jewels',
      count: 1
    },
  ]
]

【问题讨论】：

标签： mongodb aggregation-framework filtering dsa

【解决方案1】：

您可以使用$facet 对传入数据进行分类

db.collection.aggregate([
  {
    $facet: {
      categorizedByUser: [
        {
          $group: {
            _id: "$_user",
            count: {
              $sum: 1
            }
          }
        }
      ],
      categorizedByMaterial: [
        {
          $group: {
            _id: "$material",
            count: {
              $sum: 1
            }
          }
        }
      ],
      categorizedByShape: [
        {
          $group: {
            _id: "$shape",
            count: {
              $sum: 1
            }
          }
        }
      ],
      categorizedByType: [
        {
          $group: {
            _id: "$type",
            count: {
              $sum: 1
            }
          }
        }
      ]
    }
  }
])

工作Mongo playground

【讨论】：

谢谢！！对数据进行分类很好，但是如何根据查询对其进行过滤。让查询为，_user = 5f9b78bf1130ca88e2e1d material = [silver, mixed] type = [beads, Jewels] shape = [round] 过滤数据 => 分类 => 响应