本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。
$out
Amazon DocumentDB 中的$out運算子用於將彙總管道的結果寫入指定的集合。
$out 應該是管道中的最後一個階段。
參數
注意：如果集合已存在，則會將其取代為彙總階段的結果。
範例 (MongoDB Shell)
下列範例示範如何在 Amazon DocumentDB 中使用 $out運算子，將彙總管道的結果寫入新集合。
建立範例文件
db.products.insertMany([
{ _id: 1, name: "Wireless Headphones", category: "Electronics", price: 100.0 },
{ _id: 2, name: "Smartphone", category: "Electronics", price: 200.0 },
{ _id: 3, name: "JavaScript Guide", category: "Books", price: 50.0 },
{ _id: 4, name: "Database Design Handbook", category: "Books", price: 75.0 }
]);
查詢範例
db.products.aggregate([
{ $group: { _id: "$category", totalPrice: { $sum: "$price" } } },
{ $out: "product_categories" }
])
輸出
無 （結果會寫入輸出集合）。
彙總管道會依類別將產品分組，並計算每個類別的項目總價。$out 運算子會將結果寫入名為 "product_categories" 的新集合。
若要檢視輸出集合中的結果：
db.product_categories.find()
[
{ "_id" : "Books", "totalPrice" : 125 },
{ "_id" : "Electronics", "totalPrice" : 300 }
]
程式碼範例
若要檢視使用 $out命令的程式碼範例，請選擇您要使用的語言標籤：
- Node.js
-
const { MongoClient } = require('mongodb');
async function demo_out_operator() {
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');
const products = db.collection('products');
// Execute aggregation with $out - results are stored in 'product_categories' collection
await products.aggregate([
{ $group: { _id: "$category", totalPrice: { $sum: "$price" } } },
{ $out: "product_categories" }
]).toArray();
// Retrieve the results from the output collection (limited to 20 records)
const productCategories = db.collection('product_categories');
const results = await productCategories.find({}).limit(20).toArray();
console.log('Results stored in product_categories collection:', results);
await client.close();
}
demo_out_operator();
- Python
-
from pymongo import MongoClient
def demo_out_operator():
client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
db = client['test']
products = db['products']
# Execute aggregation with $out - results are stored in 'product_categories' collection
list(products.aggregate([
{ '$group': { '_id': '$category', 'totalPrice': { '$sum': '$price' } } },
{ '$out': 'product_categories' }
]))
# Retrieve the results from the output collection (limited to 20 records)
product_categories = db['product_categories']
results = list(product_categories.find({}).limit(20))
print('Results stored in product_categories collection:', results)
client.close()
demo_out_operator()
