arrays - 避免 mongodb 中的空数组元素

Question

在 MongoDb 中查询集合时如何过滤结果时避免空数组

[
  {
    "_id": ObjectId("5d429786bd7b5f4ae4a64790"),
    "extensions": {
      "outcome": "success",
      "docType": "ABC",
      "Roll No": "1"
    },
    "data": [
      {
        "Page1": [
          {
            "heading": "LIST",
            "content": [
              {
                "text": "<b>12345</b>"
              },

            ],

          }
        ],
        "highlights": [
          {
            "name": "ABCD",
            "text": "EFGH",

          }
        ],
        "marks": [
          {
            "revision": "revision 1",
            "Score": [
              {
                "maths": "100",
                "science": "40",
                "history": "90"
              },
              {
                "lab1": "25",
                "lab2": "25"
              }
            ],
            "Result": "Pass"
          },
          {
            "revision": "revision 1",
            "Score": [
              {
                "maths": "100",
                "science": "40"
              },
              {
                "lab1": "25",
                "lab2": "25"
              }
            ],
            "Result": "Pass"
          }
        ]
      }
    ]
  }
]

我正在寻找分数数组中仅具有“历史”标记的结果。

我尝试了以下查询(在 mongo 3.6.10 中)，但它返回空分数数组以及具有历史记录的数组

db.getCollection('student_scores').find({
  "data.marks.score.history": {
    $not: {
      $type: 10
    },
    $exists: true
  }
},
{
  "extensions.rollNo": 1,
  "data.marks.score.history": 1
})

期望的输出是

{
  "extensions": {
    "rollNo": "1"
  },
  "data": [
    {
      "marks": [
        {
          "Score": [
            {
              "history": "90"
            }
          ]
        }
      ]
    }
  ]
}

Answer 1

我使用了类似以下的内容；

db.getCollection('student_scores').aggregate([
  {
    $unwind: "$data"
  },
  {
    $unwind: "$data.marks"
  },
  {
    $unwind: "$data.marks.Score"
  },
  {
    $match: {
      "data.marks.Score.history": {
        $exists: true,
        $not: {
          $type: 10
        }
      }
    }
  },
  {
    $project: {
      "extensions.Roll No": 1,
      "data.marks.Score.history": 1
    }
  },
  {
    $group: {
      _id: "$extensions.Roll No",
      history_grades: {
        $push: "$data.marks.Score.history"
      }
    }
  }
])

根据您的输入，我得到了以下结果(我认为比您预期的输出更具可读性)；

[
  {
    "_id": "1",
    "history_grades": [
      "90"
    ]
  }
]

其中 _id 表示任何给定数据集的“extensions.Roll No”值。

你觉得怎么样？

check with a bigger input on mongoplayground