将元素数组缩减为 MongoDB 中的对象

【问题标题】：Reduce an array of elements into an object in MongoDB将元素数组缩减为 MongoDB 中的对象
【发布时间】：2023-02-07 16:36:17
【问题描述】：

我有一个名为 Venue 的 MongoDB 集合，其元素类型为：

{
    venue: "Grand Hall",
    sections: [{
        name: "Lobby",
        drinks: [{
            name: "Vodka",
            quantity: 3
        }, {
            name: "Red Wine",
            quantity: 1
        }]
    }, {
        name: "Ballroom",
        drinks: [{
            name: "Vodka",
            quantity: 22
        }, {
            name: "Red Wine",
            quantity: 50
        }]
    }]
}

我想计算聚会中每种饮料的总量。所以我希望我的结果是这样的：

{
    venue: "Grand Hall",
    sections: 2,
    drinks: [{
        name: "Vodka",
        quantity: 25
    }, {
        name: "Red Wine",
        quantity: 51
    }]
}

【问题讨论】：

标签： mongodb mongoose mongodb-query aggregation-framework

【解决方案1】：

$unwind - 将sections 数组解构为多个文档。
$unwind - 将sections.drinks 数组解构为多个文档。
$group - 按venue 和sections.drinks.name 分组。对quantity 进行求和。

$group - 按venue 分组。对上一阶段的分组结果进行计数。并将文档添加到drinks 数组中。

db.collection.aggregate([
  {
    $unwind: "$sections"
  },
  {
    $unwind: "$sections.drinks"
  },
  {
    $group: {
      _id: {
        venue: "$venue",
        drink_name: "$sections.drinks.name"
      },
      quantity: {
        $sum: "$sections.drinks.quantity"
      }
    }
  },
  {
    $group: {
      _id: "$venue",
      section: {
        $sum: 1
      },
      drinks: {
        $push: {
          name: "$_id.drink_name",
          quantity: "$quantity"
        }
      }
    }
  }
])

Demo @ Mongo Playground

【讨论】：