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$push - Amazon DocumentDB
示例（MongoDB Shell）窗口运算符用法示例（MongoDB Shell）代码示例

本文属于机器翻译版本。若本译文内容与英语原文存在差异，则一律以英文原文为准。

$push

$push聚合运算符返回每个组的指定表达式中所有值的数组。它通常在$group阶段内用于将值累积到数组中。

参数

  • expression：要为组中每个文档计算的表达式。

示例（MongoDB Shell）

以下示例演示使用$push运算符收集每个类别的所有产品名称。

创建示例文档 

db.sales.insertMany([
  { _id: 1, category: "Electronics", product: "Laptop", amount: 1200 },
  { _id: 2, category: "Electronics", product: "Mouse", amount: 25 },
  { _id: 3, category: "Furniture", product: "Desk", amount: 350 },
  { _id: 4, category: "Furniture", product: "Chair", amount: 150 },
  { _id: 5, category: "Electronics", product: "Keyboard", amount: 75 }
]);

查询示例 

db.sales.aggregate([
  {
    $group: {
      _id: "$category",
      products: { $push: "$product" }
    }
  }
]);

输出

[
  { _id: 'Furniture', products: [ 'Desk', 'Chair' ] },
  { _id: 'Electronics', products: [ 'Laptop', 'Mouse', 'Keyboard' ] }
]

窗口运算符用法示例（MongoDB Shell）

8.0.2 版中的新内容。

该$push操作员还可以在$setWindowFields舞台中用作窗口操作员。在此上下文中，它按排序顺序返回每个窗口中文档的指定表达式的所有值的数组。您可以在output字段下指定运算符，也可以选择使用window文档定义窗口边界。

注意

在中用作窗口运算符时$setWindowFields，中间数据限制$push为 100 MB。超过此限制的操作会返回错误。

创建示例文档 

db.purchases.insertMany([
  { _id: 1, category: "Electronics", day: 1, product: "Laptop" },
  { _id: 2, category: "Electronics", day: 2, product: "Mouse" },
  { _id: 3, category: "Electronics", day: 3, product: "Keyboard" },
  { _id: 4, category: "Furniture", day: 1, product: "Desk" },
  { _id: 5, category: "Furniture", day: 2, product: "Chair" }
]);

查询示例

以下示例对文档进行分区category，按分区排序day，并返回从分区开始到当前文档的运行product值列表。

db.purchases.aggregate([
  {
    $setWindowFields: {
      partitionBy: "$category",
      sortBy: { day: 1 },
      output: {
        productsSoFar: {
          $push: "$product",
          window: { documents: ["unbounded", "current"] }
        }
      }
    }
  }
]);

输出

[
  { "_id": 1, "category": "Electronics", "day": 1, "product": "Laptop", "productsSoFar": [ "Laptop" ] },
  { "_id": 2, "category": "Electronics", "day": 2, "product": "Mouse", "productsSoFar": [ "Laptop", "Mouse" ] },
  { "_id": 3, "category": "Electronics", "day": 3, "product": "Keyboard", "productsSoFar": [ "Laptop", "Mouse", "Keyboard" ] },
  { "_id": 4, "category": "Furniture", "day": 1, "product": "Desk", "productsSoFar": [ "Desk" ] },
  { "_id": 5, "category": "Furniture", "day": 2, "product": "Chair", "productsSoFar": [ "Desk", "Chair" ] }
]

每个文档都添加了productsSoFar按排序顺序从头到当前文档的分区内所有product值的数组。

代码示例

要查看使用$push运算符的代码示例，请选择要使用的语言的选项卡。以下示例显示了累加器的用法（输入$group）和窗口运算符的用法（输入$setWindowFields）：

Node.js
const { MongoClient } = require('mongodb');

async function example() {
  const client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
  const db = client.db('test');

  // Accumulator usage: collect all values per group
  const sales = db.collection('sales');
  await sales.insertMany([
    { _id: 1, category: "Electronics", product: "Laptop", amount: 1200 },
    { _id: 2, category: "Electronics", product: "Mouse", amount: 25 },
    { _id: 3, category: "Furniture", product: "Desk", amount: 350 },
    { _id: 4, category: "Furniture", product: "Chair", amount: 150 },
    { _id: 5, category: "Electronics", product: "Keyboard", amount: 75 }
  ]);
  const accumulatorResult = await sales.aggregate([
    {
      $group: {
        _id: "$category",
        products: { $push: "$product" }
      }
    }
  ]).toArray();
  console.log('Accumulator result:', accumulatorResult);

  // Window operator usage: running list of values within each partition
  const purchases = db.collection('purchases');
  await purchases.insertMany([
    { _id: 1, category: "Electronics", day: 1, product: "Laptop" },
    { _id: 2, category: "Electronics", day: 2, product: "Mouse" },
    { _id: 3, category: "Electronics", day: 3, product: "Keyboard" },
    { _id: 4, category: "Furniture", day: 1, product: "Desk" },
    { _id: 5, category: "Furniture", day: 2, product: "Chair" }
  ]);
  const windowResult = await purchases.aggregate([
    {
      $setWindowFields: {
        partitionBy: "$category",
        sortBy: { day: 1 },
        output: {
          productsSoFar: {
            $push: "$product",
            window: { documents: ["unbounded", "current"] }
          }
        }
      }
    }
  ]).toArray();
  console.log('Window result:', windowResult);

  await client.close();
}

example();
Python
from pymongo import MongoClient

def example():
    client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
    db = client['test']

    # Accumulator usage: collect all values per group
    sales = db['sales']
    sales.insert_many([
        { '_id': 1, 'category': 'Electronics', 'product': 'Laptop', 'amount': 1200 },
        { '_id': 2, 'category': 'Electronics', 'product': 'Mouse', 'amount': 25 },
        { '_id': 3, 'category': 'Furniture', 'product': 'Desk', 'amount': 350 },
        { '_id': 4, 'category': 'Furniture', 'product': 'Chair', 'amount': 150 },
        { '_id': 5, 'category': 'Electronics', 'product': 'Keyboard', 'amount': 75 }
    ])
    accumulator_result = list(sales.aggregate([
        {
            '$group': {
                '_id': '$category',
                'products': { '$push': '$product' }
            }
        }
    ]))
    print('Accumulator result:', accumulator_result)

    # Window operator usage: running list of values within each partition
    purchases = db['purchases']
    purchases.insert_many([
        { '_id': 1, 'category': 'Electronics', 'day': 1, 'product': 'Laptop' },
        { '_id': 2, 'category': 'Electronics', 'day': 2, 'product': 'Mouse' },
        { '_id': 3, 'category': 'Electronics', 'day': 3, 'product': 'Keyboard' },
        { '_id': 4, 'category': 'Furniture', 'day': 1, 'product': 'Desk' },
        { '_id': 5, 'category': 'Furniture', 'day': 2, 'product': 'Chair' }
    ])
    window_result = list(purchases.aggregate([
        {
            '$setWindowFields': {
                'partitionBy': '$category',
                'sortBy': { 'day': 1 },
                'output': {
                    'productsSoFar': {
                        '$push': '$product',
                        'window': { 'documents': ['unbounded', 'current'] }
                    }
                }
            }
        }
    ]))
    print('Window result:', window_result)

    client.close()

example()