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。
$底部
8.0.1 版中的新增内容。
使用$group阶段中的$bottom累加器根据指定的排序顺序返回每组排名最低的文档。
参数
示例（MongoDB Shell）
以下示例说明如何使用$bottom累加器来查找销售产品系列中每件商品的最低销售额（最低数量）。
创建示例文档
db.sales.insertMany([
{ item: "abc", quantity: 10, price: 5 },
{ item: "abc", quantity: 5, price: 8 },
{ item: "xyz", quantity: 15, price: 3 },
{ item: "xyz", quantity: 7, price: 6 }
])
查询示例
db.sales.aggregate([
{ $group: { _id: "$item", bottomSale: { $bottom: { sortBy: { quantity: -1 }, output: { quantity: "$quantity", price: "$price" } } } } }
])
输出
[
{ "_id": "xyz", "bottomSale": { "quantity": 7, "price": 6 } },
{ "_id": "abc", "bottomSale": { "quantity": 5, "price": 8 } }
]
代码示例
要查看使用$bottom运算符的代码示例，请选择要使用的语言的选项卡：
- Node.js
-
const { MongoClient } = require('mongodb');
async function example() {
const uri = 'mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false';
const client = new MongoClient(uri);
try {
await client.connect();
const db = client.db('test');
const collection = db.collection('sales');
const result = await collection.aggregate([
{ $group: { _id: "$item", bottomSale: { $bottom: { sortBy: { quantity: -1 }, output: { quantity: "$quantity", price: "$price" } } } } }
]).toArray();
console.log(result);
} catch (error) {
console.error('Error:', error);
} finally {
await client.close();
}
}
example();
- Python
-
from pymongo import MongoClient
from pprint import pprint
def example():
client = None
try:
client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
db = client['test']
collection = db['sales']
result = list(collection.aggregate([
{ '$group': { '_id': '$item', 'bottomSale': { '$bottom': { 'sortBy': { 'quantity': -1 }, 'output': { 'quantity': '$quantity', 'price': '$price' } } } } }
]))
pprint(result)
except Exception as e:
print(f"An error occurred: {e}")
finally:
if client:
client.close()
example()
