MongoDB - 计算包含数组元素的数组中的值的$sum

Question

我有一个聚合查询生成一个包含数组元素的数组。我如何 $sum 这些值并产生类似于以下内容的输出:

  { "additionalReminders": 7 }

这是一个数据结构的例子。注意一些数组元素是空的，应该被忽略或计为 0:

  {
    "additionalReminders": [
      [
        "1",
        "1"
      ],
      [],
      [],
      [
        "1"
      ],
      [],
      [
        "1"
      ],
      [],
      [
        "1"
      ],
      [],
      [
        "1"
      ],
      [],
      [],
      [
        "1"
      ]
    ]
  }

Mongo Playground : https://mongoplayground.net/p/BjSU_oYC8KG

Answer 1

这是您要查找的内容:

db.collection.aggregate([
  {
    "$unwind": "$additionalReminders"
  },
  {
    "$unwind": "$additionalReminders"
  },
  {
    $group: {
      _id: null,
      "additionalReminders": {
        $sum: {
          "$toInt": "$additionalReminders"
        }
      }
    }
  },
  {
    $project: {
      _id: false,
      additionalReminders: true
    }
  }
])

Playground :https://mongoplayground.net/p/JInbHAmc_yV

我们的想法是将您的场展开几次以获得此输出:

...
{
    "_id": ObjectId("5a934e000102030405000000"),
    "additionalReminders": "1"
  },
  {
    "_id": ObjectId("5a934e000102030405000000"),
    "additionalReminders": "1"
  },
  {
    "_id": ObjectId("5a934e000102030405000000"),
    "additionalReminders": "1"
  },
...

然后这只是对 $additionalReminders 字段求和的简单问题，但不是在我们将其转换为 Int 之前。