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Mongo:添加字段,计算另一个字段出现的次数

mongoose mongodb node.js

BeetleJuice · 技术社区 · 6 年前

我是MongoDB的新手。我正在写一个应用程序使用猫鼬和NodeJS。我从这个系列开始:

[
  { name: "Joe", hobby: "Food"},
  { name: "Lyn", hobby: "Food"},
  { name: "Rex", hobby: "Play"},
  { name: "Rex", hobby: "Shop"},
  ...
]

nameCount hobbyCount 为文档的爱好显示相同的内容:

[
  { name: "Joe", hobby: "Food", nameCount: 1, hobbyCount: 2 },
  { name: "Lyn", hobby: "Food", nameCount: 1, hobbyCount: 2 },
  { name: "Rex", hobby: "Play", nameCount: 2, hobbyCount: 1 },
  { name: "Rex", hobby: "Shop", nameCount: 2, hobbyCount: 1 }
]

通过我的研究和摆弄,我得到了下面的查询工作,但它似乎过高,低效和过于复杂。

db.members.aggregate([
  {$skip: 0},
  {$limit: 4},
  {
    $lookup: {
      from: "members",
      let: { name: "$name"},
      pipeline: [
        { $match: { $expr: { $eq: ["$name", "$$name"] } } },
        { $count: "count" }
      ],
      as: "nameCount"
    }
  },
  { $unwind: "$nameCount" },
  { $addFields: { nameCount: "$nameCount.count" } },
  {
    $lookup: {
      from: "members",
      let: { hobby: "$hobby"},
      pipeline: [
        { $match: { $expr: { $eq: ["$hobby", "$$hobby"] } } },
        { $count: "count" }
      ],
      as: "hobbyCount"
    }
  },
  { $unwind: "$hobbyCount" },
  { $addFields: { hobbyCount: "$hobbyCount.count" } }
]);

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姓名计数 和 霍比计数

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0 回复 | 直到 5 年前

Valijon 6 年前

编辑: $lookup (我们通过名字和爱好来匹配)和计数 nameCount 和 hobbyCount 通过应用 $filter $reduce 操作员

db.members.aggregate([
  {
    $skip: 1
  },
  {
    $limit: 2
  },
  {
    $lookup: {
      from: "members",
      let: {
        name: "$name",
        hobby: "$hobby"
      },
      pipeline: [
        {
          $match: {
            $expr: {
              $or: [
                {
                  $eq: [
                    "$name",
                    "$$name"
                  ]
                },
                {
                  $eq: [
                    "$hobby",
                    "$$hobby"
                  ]
                }
              ]
            }
          }
        }
      ],
      as: "count"
    }
  },
  {
    $project: {
      _id: 0,
      name: 1,
      hobby: 1,
      nameCount: {
        $reduce: {
          input: "$count",
          initialValue: 0,
          in: {
            $add: [
              "$$value",
              {
                $cond: [
                  {
                    $eq: [
                      "$name",
                      "$$this.name"
                    ]
                  },
                  1,
                  0
                ]
              }
            ]
          }
        }
      },
      hobbyCount: {
        $size: {
          $filter: {
            input: "$count",
            cond: {
              $eq: [
                "$hobby",
                "$$this.hobby"
              ]
            }
          }
        }
      }
    }
  }
])

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