Mongo 聚合 - 使用先前管道中的字段值作为排序字段进行排序

Question

我使用 mongodb 聚合生成了以下输出（包括 levelsCount 字段中的 $group 管道）：

{
    "_id" : "1",
    "name" : "First",
    "levelsCount" : [
        { "_id" : "level_One", "levelNum" : 1, "count" : 1 },
        { "_id" : "level_Three", "levelNum" : 3, "count" : 1 },
        { "_id" : "level_Four", "levelNum" : 4, "count" : 8 }
    ]
}
{
    "_id" : "2",
    "name" : "Second",
    "levelsCount" : [
        { "_id" : "level_One", "levelNum" : 1, "count" : 5 },
        { "_id" : "level_Two", "levelNum" : 2, "count" : 2 },
        { "_id" : "level_Three", "levelNum" : 3, "count" : 1 },
        { "_id" : "level_Four", "levelNum" : 4, "count" : 3 }
    ]
}
{
    "_id" : "3",
    "name" : "Third",
    "levelsCount" : [
        { "_id" : "level_One", "levelNum" : 1, "count" : 1 },
        { "_id" : "level_Two", "levelNum" : 2, "count" : 3 },
        { "_id" : "level_Three", "levelNum" : 3, "count" : 2 },
        { "_id" : "level_Four", "levelNum" : 4, "count" : 3 }
    ]
}

现在，我需要根据 levelsCount 数组元素的 levelNum 和 count 字段对这些文档进行排序。 IE。如果两个文档的 levelNum: 1 (level_One) 计数均为 5，则排序将比较 levelNum: 2 (level_Two) 字段的计数，依此类推。

我知道如何 $sort pipeline would work on multiple fields (Something like { $sort : { level_One : 1, level_Two: 1 } }), But the problem is how to access those values of levelNum of each array element and set that value as a field name to do sorting on that. (I couldn't handle it even after $unwinding levelsCount 数组）。

P.s: levelsCount 数组元素的初始顺序在每个文档中可能不同，并不重要。

编辑： 上述结构的预期输出为：

// Sorted result:
{
    "_id" : "2",
    "name" : "Second",
    "levelsCount" : [
        { "_id" : "level_One", "levelNum" : 1, "count" : 5 }, // "level_One's count: 5"  is greater than "level_One's count: 1" in two other documents, regardless of other level_* fields. Therefore this whole document with "name: Second" is ordered first.
        { "_id" : "level_Two", "levelNum" : 2, "count" : 2 },
        { "_id" : "level_Three", "levelNum" : 3, "count" : 1 },
        { "_id" : "level_Four", "levelNum" : 4, "count" : 3 }
    ]
}
{
    "_id" : "3",
    "name" : "Third",
    "levelsCount" : [
        { "_id" : "level_One", "levelNum" : 1, "count" : 1 },
        { "_id" : "level_Two", "levelNum" : 2, "count" : 3 }, // "level_Two's count" in this document exists with value (3) while the "level_Two" doesn't exist in the below document which mean (0) value for count. So this document with "name: Third" is ordered higher than the below document.
        { "_id" : "level_Three", "levelNum" : 3, "count" : 2 },
        { "_id" : "level_Four", "levelNum" : 4, "count" : 3 }
    ]
}
{
    "_id" : "1",
    "name" : "First",
    "levelsCount" : [
        { "_id" : "level_One", "levelNum" : 1, "count" : 1 },
        { "_id" : "level_Three", "levelNum" : 3, "count" : 1 },
        { "_id" : "level_Four", "levelNum" : 4, "count" : 8 }
    ]
}

当然，我更希望有以下格式的输出文档，但第一个问题是对所有文档进行排序：

{
    "_id" : "1",
    "name" : "First",
    "levelsCount" : [
        { "level_One" : 1 },
        { "level_Three" : 1 },
        { "level_Four" : 8 }
    ]
}

Answer 1

您可以按 levelNum 降序排序，count 升序排序，

db.collection.aggregate([
  {
    $sort: {
      "levelsCount.levelNum": -1,
      "levelsCount.count": 1
    }
  }
])

Playground

对于levelsCount数组的键值格式结果，

$map 迭代 levelsCount 数组
准备键值对数组并使用$arrayToObject

  {
    $addFields: {
      levelsCount: {
        $map: {
          input: "$levelsCount",
          in: {
            $arrayToObject: [
              [{ k: "$$this._id", v: "$$this.levelNum" }]
            ]
          }
        }
      }
    }
  }

Playground

Mongo 聚合 - 使用先前管道中的字段值作为排序字段进行排序

Mongo aggregation - Sorting using a field value from previous pipeline as the sort field

sorting

grouping

mongodb

aggregation-framework