Consume a change feed from within an application by using the SDK

The Azure Cosmos DB change feed allows you to consume and react to changes in your database in real-time. By using the SDK for Azure Cosmos DB, you can easily integrate the change feed into your application. This article will guide you through the steps to consume a change feed from within your application using the SDK.

Step 1: Initialize the Cosmos DB Client

To get started, you need to initialize the Azure Cosmos DB client in your application. This client will be used to interact with the database and consume the change feed. Here’s an example of how to initialize the client using the C# SDK:

using Microsoft.Azure.Cosmos;
using Microsoft.Azure.Cosmos.ChangeFeed;

string connectionString = "";
CosmosClient cosmosClient = new CosmosClient(connectionString);


Step 2: Get the Database and Container References

Next, you need to obtain references to the specific database and container within Azure Cosmos DB. This will allow you to listen for changes in the desired container. Here’s an example:

string databaseName = "";
string containerName = "";

Database database = await cosmosClient.GetDatabase(databaseName).InitializeAsync();
Container container = await database.GetContainer(containerName).InitializeAsync();


Step 3: Enable Change Feed Processor on the Container

Now that you have the container reference, you can enable the change feed processor on it. The change feed processor will receive the change events and allow you to process them within your application. Here’s an example:

ChangeFeedProcessor changeFeedProcessor = container.GetChangeFeedProcessorBuilder("MyProcessorName", HandleChangesAsync)
.WithInstanceName("MyInstance")
.WithLeaseContainer(leaseContainer)
.Build();

// Handle change events
async Task HandleChangesAsync(IReadOnlyCollection changes, CancellationToken cancellationToken)
{
foreach (ChangeFeedProcessorContext change in changes)
{
Console.WriteLine($"Detected operation for item with id: {change.GetResource().Id}");
// Process change event
// Your custom logic here
}
await changeFeedProcessor.CheckpointAsync(cancellationToken);
}


Step 4: Start the Change Feed Processor

Once the change feed processor is set up, you can start consuming the change feed events by starting the processor. Here’s how to start the change feed processor:

await changeFeedProcessor.StartAsync();

Optional: Stop the Change Feed Processor

If you want to stop consuming the change feed events at any point, you can stop the change feed processor. Here’s an example:

await changeFeedProcessor.StopAsync();

Now, your application is ready to consume change feed events from the specified Azure Cosmos DB container. You can customize the handling logic to meet your specific requirements.

Note:

• Replace with the connection string for your Azure Cosmos DB account.
• Replace with the name of your database.
• Replace with the name of your container.

The change feed processor enables you to listen to changes in your Azure Cosmos DB container and react to them in real-time. It eliminates the need for continuous polling of the database for updates, making your application more efficient and responsive.

By incorporating the change feed processor into your application, you can easily build event-driven architectures, real-time analytics, and workflows triggered by data changes. The Azure Cosmos DB change feed provides a powerful mechanism for building reactive applications that respond to changes in your database.