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。
$addToSet
$addToSet 彙總運算子會從每個群組的指定表達式傳回唯一值的陣列。它會在$group階段內用來累積不同的值，自動消除重複項目。
參數
範例 (MongoDB Shell)
下列範例示範如何使用 $addToSet 運算子來收集為每位客戶下訂單的唯一城市。
建立範例文件
db.orders.insertMany([
{ _id: 1, customer: "Alice", city: "Seattle", amount: 100 },
{ _id: 2, customer: "Alice", city: "Portland", amount: 150 },
{ _id: 3, customer: "Bob", city: "Seattle", amount: 200 },
{ _id: 4, customer: "Alice", city: "Seattle", amount: 75 },
{ _id: 5, customer: "Bob", city: "Boston", amount: 300 }
]);
查詢範例
db.orders.aggregate([
{
$group: {
_id: "$customer",
cities: { $addToSet: "$city" }
}
}
]);
輸出
[
{ _id: 'Bob', cities: [ 'Seattle', 'Boston' ] },
{ _id: 'Alice', cities: [ 'Seattle', 'Portland' ] }
]
程式碼範例
若要檢視使用$addToSet彙總運算子的程式碼範例，請選擇您要使用的語言標籤：
- Node.js
-
const { MongoClient } = require('mongodb');
async function 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');
const collection = db.collection('orders');
const result = await collection.aggregate([
{
$group: {
_id: "$customer",
cities: { $addToSet: "$city" }
}
}
]).toArray();
console.log(result);
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']
collection = db['orders']
result = list(collection.aggregate([
{
'$group': {
'_id': '$customer',
'cities': { '$addToSet': '$city' }
}
}
]))
print(result)
client.close()
example()
