MongoDB罗盘-从文档中的3个字段及其值中获取最大值的字段名称（键）

debugcn 发表于 Dev

Zookastos

我有这个样本mongodb文件-

{
    _id: 5db85ee97d9fb13ead4fc54c
    applId: 5d48f34f7d9fb10ce171f905
    fileId: "dd386cf7-4139-45c2-9853-cbb126621b51"
    job: Object
    country: "US"
    fullName: "abcd xyz"
    htmlWordCount: 2766
    textWordCount: 1867
    rchilliTextWordCount: 2840
    deleted: 0
    dateEntered: 2019-10-29 15:46:49.237
    dateModified: 2019-10-29 15:46:49.237
}

我想在罗盘中建立查询，以便在输出中包含以下字段-

{
    _id: 5db85ee97d9fb13ead4fc54c
    country: "US"
    fullName: "abcd xyz"
    htmlWordCount: 2766
    textWordCount: 1867
    rchilliTextWordCount: 2840
    winner: "rchilliTextWordCount"
}

请注意，它有一个名为“ winner”的新字段，该字段总是返回最大字数的列（3"htmlWordCount", "textWordCount", "rchilliTextWordCount"列之内）。此新列"winner"将在运行时根据查询生成。同样，此查询在上过滤country = "US"。

如何在MongoDB Compass中执行此操作，或者聚合管道应该是什么样？

瓦利洪

您可以使用$ switch或$ cond

db.collection.aggregate([
  {
    $match: {
      country: "US"
    }
  },
  {
    $project: {
      country: 1,
      fullName: 1,
      htmlWordCount: 1,
      textWordCount: 1,
      rchilliTextWordCount: 1,
      winner: {
        $switch: {
          branches: [
            {
              case: {
                $and: [
                  {
                    $gt: [
                      "$htmlWordCount",
                      "$textWordCount"
                    ]
                  },
                  {
                    $gt: [
                      "$htmlWordCount",
                      "$rchilliTextWordCount"
                    ]
                  }
                ]
              },
              then: "htmlWordCount"
            },
            {
              case: {
                $and: [
                  {
                    $gt: [
                      "$textWordCount",
                      "$htmlWordCount"
                    ]
                  },
                  {
                    $gt: [
                      "$textWordCount",
                      "$rchilliTextWordCount"
                    ]
                  }
                ]
              },
              then: "textWordCount"
            },
            {
              case: {
                $and: [
                  {
                    $gt: [
                      "$rchilliTextWordCount",
                      "$htmlWordCount"
                    ]
                  },
                  {
                    $gt: [
                      "$rchilliTextWordCount",
                      "$textWordCount"
                    ]
                  }
                ]
              },
              then: "rchilliTextWordCount"
            }
          ],
          default: "No winners"
        }
      }
    }
  }
])