MongoDB 对数组中的元素进行分组

Question

我想要，对于每个 product_id，所有订单中的价格总和，我想要实现的另一个结果是同一数组中具有相同 ID 的产品的价格总和。

\orders collection:
{
order_id: 123,
customer_id: 1,
order_items: [{product_id:1, price: 2}, {product: 4, price: 8}, {product_id:1, price: 2}]
},
{
order_id: 124,
customer_id: 5,
order_items: [{product_id:5, price: 7}, {product: 4, price: 8}]
}

我想要的第一个结果：

{product_id: 1, tot_price: 4}, 
{product_id: 4, tot_price: 16},
{product_id: 5, tot_price: 7}

第二个结果：

{order_id:123,
product_tot: [{product_id:1, tot_price: 4}, {product: 4, tot_price: 8}]},
{order_id:124,
product_tot: [{product_id:5, tot_price: 7}, {product: 4, tot_price: 8}},

Answer 1

尝试以下查询：

第一个结果：

db.collection.aggregate([
  {
    $unwind: {
      path: "$order_items",
      preserveNullAndEmptyArrays: true
    }
  },
  {
    $group: {
      _id: "$order_items.product_id",
      tot_price: {
        $sum: "$order_items.price"
      }
    }
  },
  {
    $project: {
      _id: 0,
      product_id: "$_id",
      tot_price: 1
    }
  }
])

MongoPlayGroundLink

第二个结果：

db.collection.aggregate([
  {
    $unwind: {
      path: "$order_items",
      preserveNullAndEmptyArrays: true
    }
  },
  {
    $group: {
      _id: {
        order_id: "$order_id",
        product_id: "$order_items.product_id"
      },
      tot_price: {
        $sum: "$order_items.price"
      }
    }
  },
  {
    $project: {
      _id: 0,
      order_id: "$_id.order_id",
      product_id: "$_id.product_id",
      tot_price: "$tot_price"
    }
  },
  {
    $group: {
      _id: "$order_id",
      product_tot: {
        $push: {
          product_id: "$product_id",
          tot_price: "$tot_price"
        }
      }
    }
  },
  {
    $project: {
      _id: 0,
      order_id: "$_id",
      product_tot: 1
    }
  }
])

MongoPlayGroundLink

MongoDB 对数组中的元素进行分组

MongoDB group elements in an array

group-by

embedded-database

mongodb