Mongodb 根据参考图计算子文档列表的最大值

你的分类dict不适合mongo，因为mongo要求对象有字符串类型的键.为了更容易处理，您可以将词典整理为以下表格:

[
  {
    category: 1,
    fruits: [
      "apple"
    ]
  },
  {
    category: 2,
    fruits: [
      "banana",
      "kiwi"
    ]
  },
  {
    category: 3,
    fruits: [
      "pineapple",
      "strawberry"
    ]
  }
]

在聚合管道中，按$reduce迭代带参数的类别数组以有条件地更新累加器，以获得最大匹配类别.

db.collection.aggregate([
  {
    "$unwind": "$shops"
  },
  {
    "$set": {
      "max_category": {
        "$reduce": {
          "input": [
            {
              category: 1,
              fruits: [
                "apple"
              ]
            },
            {
              category: 2,
              fruits: [
                "banana",
                "kiwi"
              ]
            },
            {
              category: 3,
              fruits: [
                "pineapple",
                "strawberry"
              ]
            }
          ],
          "initialValue": null,
          "in": {
            "$cond": {
              "if": {
                $and: [
                  {
                    $gt: [
                      "$$this.category",
                      "$$value"
                    ]
                  },
                  {
                    $gt: [
                      {
                        $size: {
                          "$setIntersection": [
                            "$$this.fruits",
                            "$shops.fruits"
                          ]
                        }
                      },
                      0
                    ]
                  }
                ]
              },
              "then": "$$this.category",
              "else": "$$value"
            }
          }
        }
      }
    }
  },
  {
    "$group": {
      "_id": "$_id",
      "country": {
        $first: "$country"
      },
      "max_category": {
        $max: "$max_category"
      },
      "shops": {
        "$push": "$shops"
      }
    }
  }
])

Mongo Playground个