Monitor Data Changes

You can open a change stream on a Collection, Database, or Client by using the Watch() method.

Example

Tip

Read the Usage Examples to learn how to run this example.

The following example opens a change stream on the restaurants collection and prints inserted documents:

coll := client.Database("sample_restaurants").Collection("restaurants")
// Creates instructions to watch for insert operations
pipeline := mongo.Pipeline{bson.D{{"$match", bson.D{{"operationType", "insert"}}}}}
// Creates a change stream that receives change events
cs, err := coll.Watch(context.TODO(), pipeline)
if err != nil {
	panic(err)
}
defer cs.Close(context.TODO())
fmt.Println("Waiting For Change Events. Insert something in MongoDB!")
// Prints a message each time the change stream receives an event
for cs.Next(context.TODO()) {
	var event bson.M
	if err := cs.Decode(&event); err != nil {
		panic(err)
	}
	output, err := json.MarshalIndent(event["fullDocument"], "", "    ")
	if err != nil {
		panic(err)
	}
	fmt.Printf("%s\n", output)
}
if err := cs.Err(); err != nil {
	panic(err)
}

View a fully runnable example.

Expected Result

After you run the full example, run the Insert a Document usage example in a different shell. Once you run the insert operation, you should see the following output:

// results truncated
{
  "_id": ...,
  "name": "8282",
  "cuisine": "Korean"
}

Important

Make sure to shut down this usage example once you finish by closing your terminal.

Additional Information

To learn more about opening a change stream and handling potential errors, see:

Fundamentals page on change streams
MongoDB Server Manual Change Streams Documentation

API Documentation

Watch()

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Bulk Operations

Count Documents