排序并将序列号添加到mongodb中的嵌套项

Question

我有以下文档的 MongoDB 集合：

{
    "name": "First parent",
    "items": [
        { "name": "First child", "value": 32 },
        { "name": "Second child", "value": 76 },
        { "name": "Third child", "value": 13 }
    ]
}
{
    "name": "Second parent",
    "items": [
        { "name": "Fifth child", "value": 16 },
        { "name": "Sixth child", "value": 15 }
    ]
}
{
    "name": "Third parent",
    "items": [
        { "name": "Fourth child", "value": 56 }
    ]
}

我想：

• 从 (desc) 的每个父级中按 items.value 对子级进行排序，
• 按items.value 的第一个（最高）孩子（desc）对父母进行排序，
• 为每个孩子添加items.order。

所以期望的输出应该是：

{
    "name": "First parent",
    "items": [
        { "name": "Second child", "value": 76, "order": 1 }, // Should be first in array, because 76 < 32 < 13. Should have order: 1, because 76 is highest value of all children in collection.
        { "name": "First child", "value": 32, "order": 3 },
        { "name": "Third child", "value": 13, "order": 6 }
    ]
}
{
    "name": "Third parent",
    "items": [
        { "name": "Fourth child", "value": 56, "order": 2 } // Should have order: 2, because 56 is second highest value of all children in collection.
    ]
}
{
    "name": "Second parent",
    "items": [
        { "name": "Fifth child", "value": 16, "order": 4 },
        { "name": "Sixth child", "value": 15, "order": 5 }
    ]
}

有没有办法做到这一点？我只有这个（没有items.order 属性）：

db.collection.aggregate([
    { "$unwind": "$items" },
    { "$sort": { "items.value": -1 } },
    { "$group": {
        "_id": "$_id",
        "name": { "$first": "$name" },
        "items": { "$push": "$items" }}
    },
    { "$sort": { "items.value": -1 } }
])

Answer 1

引入一个key来获取item数组的第一个元素的第一个值。然后按它排序。

[
  {
    "$unwind": {
      path: "$items"
    }
  },
  {
    "$sort": {
      "items.value": -1
    }
  },
  {
    "$group": {
      "_id": "$_id",
      "name": {
        "$first": "$name"
      },
      topValue: {
        $first: "$items.value"
      },
      "items": {
        "$push": "$items"
      }
    }
  },
  {
    "$sort": {
      "topValue": -1
    }
  },
  {
    "$project": {
      topValue: 0
    }
  }
]

工作Mongo playground