MongoDB 聚合管道

嗨，外星人！我是帕万。因此，在这个存储库中，我将通过基本示例深入解释所有聚合阶段。我还将提供进一步学习资源的链接。

所以这个存储库包含各种 MongoDB 聚合管道的 JSON 文件。这些管道演示了如何使用不同的聚合阶段和操作来处理和分析数据。

目录

• 简介
• CRUD 操作
• 聚合阶段
  • $匹配
  • $组
  • $项目
  • $排序
  • $限额
  • $跳过
  • $查找
  • $放松
  • $addFields
  • $replaceRoot
• 聚合操作
  • $总和
  • 平均$
  • $分钟
  • $max
  • $第一
  • $最后
• 示例数据集
• 进一步学习的资源

介绍

MongoDB 中的聚合是处理和分析存储在集合中的数据的强大方法。它允许您执行过滤、分组、排序和转换数据等操作。

增删改查操作

创造

db.orders.insertOne({
  "order_id": 26,
  "cust_id": 1006,
  "status": "A",
  "amount": 275,
  "items": ["apple", "banana"],
  "date": "2023-01-26"
});

读

db.orders.find().pretty();

更新

db.orders.updateOne(
  { "order_id": 2 },
  {
    $set: { "status": "C", "amount": 500 },
    $currentDate: { "lastModified": true }
  }
);

删除

db.orders.deleteOne({ "order_id": 1 });

聚合阶段

$匹配

过滤文档，仅将符合指定条件的文档传递到下一个管道阶段。

db.orders.aggregate([
  { $match: { "status": "A" } }
]);

$组

按指定的 _id 表达式对输入文档进行分组，并针对每个不同的分组输出一个文档。 _id 字段包含唯一的分组依据值。

db.orders.aggregate([
  {
    $group: {
      _id: "$cust_id",
      totalSpent: { $sum: "$amount" }
    }
  }
]);

$项目

将带有请求字段的文档传递到管道的下一阶段。

db.orders.aggregate([
  { $project: { "order_id": 1, "items": 1, "_id": 0 } }
]);

$排序

对所有输入文档进行排序，并按排序顺序将它们返回到管道。

db.orders.aggregate([
  { $sort: { "amount": -1 } }
]);

$限额

限制传递到管道中下一阶段的文档数量。

db.orders.aggregate([
  { $limit: 5 }
]);

$跳过

跳过前 n 个文档，并将剩余文档传递到管道中的下一阶段。

db.orders.aggregate([
  { $skip: 5 }
]);

$查找

对同一数据库中的另一个集合执行左外连接，以过滤“已连接”集合中的文档进行处理。

db.orders.aggregate([
  {
    $lookup: {
      from: "orderDetails",
      localField: "order_id",
      foreignField: "order_id",
      as: "details"
    }
  }
]);

$放松

从输入文档中解构数组字段，以输出每个元素的文档。

db.orders.aggregate([
  { $unwind: "$items" }
]);

$addFields

向文档添加新字段。

db.orders.aggregate([
  { $addFields: { totalWithTax: { $multiply: ["$amount", 1.1] } } }
]);

$replaceRoot

用指定文档替换输入文档。

db.orders.aggregate([
  { $replaceRoot: { newRoot: "$items" } }
]);

聚合操作

$总和

计算并返回数值的总和。 $sum 忽略非数字值。

db.orders.aggregate([
  {
    $group: {
      _id: "$cust_id",
      totalSpent: { $sum: "$amount" }
    }
  }
]);

平均$

计算并返回数值的平均值。

db.orders.aggregate([
  {
    $group: {
      _id: "$cust_id",
      averageSpent: { $avg: "$amount" }
    }
  }
]);

分钟$

返回数值中的最小值。

db.orders.aggregate([
  {
    $group: {
      _id: "$cust_id",
      minSpent: { $min: "$amount" }
    }
  }
]);

最高$

返回数值中的最大值。

db.orders.aggregate([
  {
    $group: {
      _id: "$cust_id",
      maxSpent: { $max: "$amount" }
    }
  }
]);

$第一

返回每个组文档中的第一个值。

db.orders.aggregate([
  {
    $group: {
      _id: "$cust_id",
      firstOrder: { $first: "$amount" }
    }
  }
]);

$最后

返回每个组文档中的最后一个值。

db.orders.aggregate([
  {
    $group: {
      _id: "$cust_id",
      lastOrder: { $last: "$amount" }
    }
  }
]);

示例数据集

用于执行 CRUD 和聚合操作的示例文档：

[
  { "order_id": 1, "cust_id": 1001, "status": "A", "amount": 250, "items": ["apple", "banana"], "date": "2023-01-01" },
  { "order_id": 2, "cust_id": 1002, "status": "B", "amount": 450, "items": ["orange", "grape"], "date": "2023-01-02" },
  { "order_id": 3, "cust_id": 1001, "status": "A", "amount": 300, "items": ["apple", "orange"], "date": "2023-01-03" },
  { "order_id": 4, "cust_id": 1003, "status": "A", "amount": 150, "items": ["banana", "grape"], "date": "2023-01-04" },
  { "order_id": 5, "cust_id": 1002, "status": "C", "amount": 500, "items": ["apple", "banana"], "date": "2023-01-05" },
  { "order_id": 6, "cust_id": 1004, "status": "A", "amount": 350, "items": ["orange", "banana"], "date": "2023-01-06" },
  { "order_id": 7, "cust_id": 1005, "status": "B", "amount": 200, "items": ["grape", "banana"], "date": "2023-01-07" },
  { "order_id": 8, "cust_id": 1003, "status": "A", "amount": 100, "items": ["apple", "orange"], "date": "2023-01-08" },
  { "order_id": 9, "cust_id": 1004, "status": "C", "amount": 400, "items": ["banana", "grape"], "date": "2023-01-09" },
  { "order_id": 10, "cust_id": 1001, "status": "A", "amount": 250, "items": ["apple", "grape"], "date": "2023-01-10" },
  { "order_id": 11, "cust_id": 1002, "status": "B", "amount": 350, "items": ["orange", "banana"], "date": "2023-01-11" },
  { "order_id": 12, "cust_id": 1003, "status": "A", "amount": 450, "items": ["apple", "orange"], "date": "2023-01-12" },
  { "order_id": 13, "cust_id": 1005, "status": "A", "amount": 150, "items": ["banana", "grape"], "date": "2023-01-13" },
  { "order_id": 14, "cust_id": 1004, "status": "C

", "amount": 500, "items": ["apple", "banana"], "date": "2023-01-14" },
  { "order_id": 15, "cust_id": 1002, "status": "A", "amount": 300, "items": ["orange", "grape"], "date": "2023-01-15" },
  { "order_id": 16, "cust_id": 1003, "status": "B", "amount": 200, "items": ["apple", "banana"], "date": "2023-01-16" },
  { "order_id": 17, "cust_id": 1001, "status": "A", "amount": 250, "items": ["orange", "grape"], "date": "2023-01-17" },
  { "order_id": 18, "cust_id": 1005, "status": "A", "amount": 350, "items": ["apple", "banana"], "date": "2023-01-18" },
  { "order_id": 19, "cust_id": 1004, "status": "C", "amount": 400, "items": ["orange", "grape"], "date": "2023-01-19" },
  { "order_id": 20, "cust_id": 1001, "status": "B", "amount": 150, "items": ["apple", "orange"], "date": "2023-01-20" },
  { "order_id": 21, "cust_id": 1002, "status": "A", "amount": 500, "items": ["banana", "grape"], "date": "2023-01-21" },
  { "order_id": 22, "cust_id": 1003, "status": "A", "amount": 450, "items": ["apple", "banana"], "date": "2023-01-22" },
  { "order_id": 23, "cust_id": 1004, "status": "B", "amount": 350, "items": ["orange", "banana"], "date": "2023-01-23" },
  { "order_id": 24, "cust_id": 1005, "status": "A", "amount": 200, "items": ["grape", "banana"], "date": "2023-01-24" },
  { "order_id": 25, "cust_id": 1001, "status": "A", "amount": 300, "items": ["apple", "orange"], "date": "2023-01-25" }
]

进一步学习的资源

• MongoDB 聚合文档
• MongoDB 大学课程
• MongoDB 聚合管道生成器

请随意克隆此存储库并尝试提供的聚合管道。如果您有任何问题或建议，请提出问题或提交拉取请求。

$组

按状态对订单进行分组，并计算每个状态的总金额和平均金额。

db.orders.aggregate([
  {
    $group: {
      _id: "$status",
      totalAmount: { $sum: "$amount" },
      averageAmount: { $avg: "$amount" }
    }
  }
]);

$项目

投影订单 ID、客户 ID 和含税总额的计算字段（假设税费为 10%）。

db.orders.aggregate([
  {
    $project: {
      "order_id": 1,
      "cust_id": 1,
      "totalWithTax": { $multiply: ["$amount", 1.1] }
    }
  }
]);

$排序

首先按状态升序对订单进行排序，然后按金额降序排序。

db.orders.aggregate([
  { $sort: { "status": 1, "amount": -1 } }
]);

$限额

将结果限制为金额最高的前 3 个订单。

db.orders.aggregate([
  { $sort: { "amount": -1 } },
  { $limit: 3 }
]);

$跳过

跳过前 5 个订单并返回其余订单。

db.orders.aggregate([
  { $skip: 5 }
]);

$查找

将订单集合与 orderDetails 集合连接起来以添加订单详细信息。

db.orders.aggregate([
  {
    $lookup: {
      from: "orderDetails",
      localField: "order_id",
      foreignField: "order_id",
      as: "details"
    }
  }
]);

$unwind

Deconstructs the items array in each order to output a document for each item.

db.orders.aggregate([
  { $unwind: "$items" }
]);

$addFields

Adds a new field discountedAmount which is 90% of the original amount.

db.orders.aggregate([
  { $addFields: { discountedAmount: { $multiply: ["$amount", 0.9] } } }
]);

$replaceRoot

Replaces the root document with the items array.

db.orders.aggregate([
  { $replaceRoot: { newRoot: "$items" } }
]);

$sum

Calculates the total amount for all orders.

db.orders.aggregate([
  {
    $group: {
      _id: null,
      totalAmount: { $sum: "$amount" }
    }
  }
]);

$avg

Calculates the average amount spent per order.

db.orders.aggregate([
  {
    $group: {
      _id: null,
      averageAmount: { $avg: "$amount" }
    }
  }
]);

$min

Finds the minimum amount spent on an order.

db.orders.aggregate([
  {
    $group: {
      _id: null,
      minAmount: { $min: "$amount" }
    }
  }
]);

$max

Finds the maximum amount spent on an order.

db.orders.aggregate([
  {
    $group: {
      _id: null,
      maxAmount: { $max: "$amount" }
    }
  }
]);

$first

Gets the first order placed (by date).

db.orders.aggregate([
  { $sort: { "date": 1 } },
  {
    $group: {
      _id: null,
      firstOrder: { $first: "$$ROOT" }
    }
  }
]);

$last

Gets the last order placed (by date).

db.orders.aggregate([
  { $sort: { "date": -1 } },
  {
    $group: {
      _id: null,
      lastOrder: { $last: "$$ROOT" }
    }
  }
]);

So, we have covered basic CRUD operations, all major aggregation stages, and operations, and looked into resources for further learning.

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