MongoDB Watch Collection

MongoDB Watch Collection

In MongoDB, the watch operation is used to open a change stream on a collection. This method is essential for real-time monitoring of data changes in MongoDB collections.

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Syntax

db.collection.watch(pipeline, options)

The watch method takes an optional pipeline parameter to specify an aggregation pipeline for filtering the change events and an optional options parameter to customize the change stream.

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Example MongoDB Watch Collection

Let's look at some examples of how to use the watch method in the programGuru collection in MongoDB:

1. Watch Collection for Changes

const changeStream = db.programGuru.watch();
changeStream.on('change', (change) => {
    printjson(change);
});

This command opens a change stream on the programGuru collection and prints each change event to the console.

2. Watch Collection with a Pipeline

const pipeline = [
    { $match: { 'fullDocument.age': { $gt: 30 } } }
];
const changeStream = db.programGuru.watch(pipeline);
changeStream.on('change', (change) => {
    printjson(change);
});

This command opens a change stream on the programGuru collection and prints change events where the age field is greater than 30.

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Full Example

Let's go through a complete example that includes switching to a database, creating a collection, inserting documents, and opening a change stream to watch for changes.

Step 1: Switch to a Database

This step involves switching to a database named myDatabase.

use myDatabase

In this example, we switch to the myDatabase database.

Step 2: Create a Collection

This step involves creating a new collection named programGuru in the myDatabase database.

db.createCollection("programGuru")

Here, we create a collection named programGuru.

Step 3: Insert Documents into the Collection

This step involves inserting documents into the programGuru collection.

db.programGuru.insertMany([
    { name: "John Doe", age: 30, email: "john.doe@example.com" },
    { name: "Jane Smith", age: 25, email: "jane.smith@example.com" },
    { name: "Jim Brown", age: 35, email: "jim.brown@example.com" }
])

We insert multiple documents into the programGuru collection.

Step 4: Watch Collection for Changes

This step involves using the watch method to open a change stream on the programGuru collection and monitor changes.

Watch Collection for All Changes

const changeStream = db.programGuru.watch();
changeStream.on('change', (change) => {
    printjson(change);
});

We open a change stream on the programGuru collection and print each change event to the console.

Watch Collection with a Pipeline

const pipeline = [
    { $match: { 'fullDocument.age': { $gt: 30 } } }
];
const changeStream = db.programGuru.watch(pipeline);
changeStream.on('change', (change) => {
    printjson(change);
});

We open a change stream on the programGuru collection and print change events where the age field is greater than 30.

Conclusion

The MongoDB watch operation is crucial for real-time monitoring of data changes in collections. Understanding how to use this method allows you to efficiently track and respond to changes within your MongoDB collections.