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$changeStream
弹性集群不支持。
$changeStream聚合阶段会打开更改流游标，以监视集合的实时更改。当进行插入、更新、替换或删除操作时，它会返回更改事件文档。
参数
-
fullDocument：指定是否返回完整文档以进行更新操作。选项有 default 或 updateLookup。
-
resumeAfter: 可选。恢复令牌以从变更流中的特定点继续。
-
startAtOperationTime: 可选。开始变更流的时间戳。
-
allChangesForCluster: 可选。布尔值。何时true，监视集群中的所有更改（对于管理员数据库）。当false（默认）时，仅监视指定的集合。
示例（MongoDB 外壳）
以下示例演示了如何使用$changeStream舞台来监视集合的更改。
查询示例
// Open change stream first
const changeStream = db.inventory.aggregate([
{ $changeStream: { fullDocument: "updateLookup" } }
]);
// In another session, insert a document
db.inventory.insertOne({ _id: 1, item: "Widget", qty: 10 });
// Back in the first session, read the change event
if (changeStream.hasNext()) {
print(tojson(changeStream.next()));
}
输出
{
_id: { _data: '...' },
operationType: 'insert',
clusterTime: Timestamp(1, 1234567890),
fullDocument: { _id: 1, item: 'Widget', qty: 10 },
ns: { db: 'test', coll: 'inventory' },
documentKey: { _id: 1 }
}
代码示例
要查看使用$changeStream聚合阶段的代码示例，请选择要使用的语言对应的选项卡：
- 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('inventory');
// Open change stream
const changeStream = collection.watch([]);
changeStream.on('change', (change) => {
console.log('Change detected:', change);
});
// Simulate insert in another operation
setTimeout(async () => {
await collection.insertOne({ _id: 1, item: 'Widget', qty: 10 });
}, 1000);
// Keep connection open to receive changes
// In production, handle cleanup appropriately
}
example();
- Python
-
from pymongo import MongoClient
import threading
import time
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['inventory']
# Open change stream
change_stream = collection.watch([])
# Insert document in separate thread after delay
def insert_doc():
time.sleep(1)
collection.insert_one({'_id': 1, 'item': 'Widget', 'qty': 10})
threading.Thread(target=insert_doc).start()
# Watch for changes
for change in change_stream:
print('Change detected:', change)
break # Exit after first change
client.close()
example()
