Real-time Applications - (CosmosDB Change Feed)

Real-time applications are becoming increasingly popular as users demand data and updates in real-time. One way to build real-time applications is through the use of change feeds, which allow you to stream data changes in your database to your application. In this tutorial, we'll discuss how to use the Azure Cosmos DB Change Feed to build real-time applications.

Syntax

The syntax for using the Cosmos DB Change Feed is as follows:

var feedOptions = new ChangeFeedOptions()
{
    StartFromBeginning = true,
    RequestContinuation = null,
    MaxItemCount = -1,
    LeaseOptions = new ChangeFeedLeaseOptions()
    {
        LeasePrefix = "prefix",
        LeaseExpirationInterval = TimeSpan.FromSeconds(60)
    }
};

var documentCollectionInfo = new DocumentCollectionInfo
{
    CollectionName = "mycollection",
    ConnectionPolicy = new ConnectionPolicy
    {
        ConnectionMode = ConnectionMode.Direct
    }
};

DocumentCollection documentCollection = await client.CreateDocumentCollectionIfNotExistsAsync(
    UriFactory.CreateDatabaseUri("mydatabase"),
    documentCollectionInfo);

IDocumentQuery<Document> documentQuery = client.CreateDocumentChangeFeedQuery(
    documentCollection.SelfLink,
    feedOptions);

while (documentQuery.HasMoreResults)
{
    FeedResponse<Document> feedResponse = await documentQuery.ExecuteNextAsync<Document>();
    Console.WriteLine("Inserted document {0}", feedResponse.Count);
}

Example

Let's say we have a Cosmos DB collection named mycollection and want to build a real-time application using the Change Feed. We can do this as follows:

var feedOptions = new ChangeFeedOptions()
{
    StartFromBeginning = true,
    RequestContinuation = null,
    MaxItemCount = -1,
    LeaseOptions = new ChangeFeedLeaseOptions()
    {
        LeasePrefix = "prefix",
        LeaseExpirationInterval = TimeSpan.FromSeconds(60)
    }
};

var documentCollectionInfo = new DocumentCollectionInfo
{
    CollectionName = "mycollection",
    ConnectionPolicy = new ConnectionPolicy
    {
        ConnectionMode = ConnectionMode.Direct
    }
};

DocumentCollection documentCollection = await client.CreateDocumentCollectionIfNotExistsAsync(
    UriFactory.CreateDatabaseUri("mydatabase"),
    documentCollectionInfo);

IDocumentQuery<Document> documentQuery = client.CreateDocumentChangeFeedQuery(
    documentCollection.SelfLink,
    feedOptions);

while (documentQuery.HasMoreResults)
{
    FeedResponse<Document> feedResponse = await documentQuery.ExecuteNextAsync<Document>();
    Console.WriteLine("Inserted document {0}", feedResponse.Count);
}

In this example, we are setting feedOptions to specify that we want to start from the beginning of the feed, with no continuation, and no limit on item count. We are also setting the lease prefix to "prefix" with an expiration interval of 60 seconds.

We then create a DocumentCollection object and a documentQuery object using the CreateDocumentChangeFeedQuery method, passing in the documentCollection.SelfLink and feedOptions.

Finally, we loop through the change feed using documentQuery.HasMoreResults and documentQuery.ExecuteNextAsync<Document>(), printing the number of inserted documents to the console.

Explanation

The Azure Cosmos DB Change Feed allows you to stream data changes in your database to your application in real-time. This allows you to build real-time applications that can respond to data changes immediately.

The example above shows how to use the Change Feed SDKs to read the change feed for a Cosmos DB collection. The SDKs provide a simple looping mechanism to keep reading changes in the collection.

Use

The Cosmos DB Change Feed can be used to build many different types of real-time applications, such as chat applications, real-time analytics dashboards, and real-time notifications.

Important Points

Here are some important points to keep in mind when using the Cosmos DB Change Feed in your real-time applications:

• The Change Feed can be used for both reactive and proactive scenarios, reacting to changes in the system or proactively obtaining changes without polling.
• The Change Feed can be used with different Azure services, including Azure Functions and Azure Stream Analytics.
• The Cosmos DB Change Feed can help you build real-time applications that provide up-to-date data in real-time.

Summary

In this tutorial, we discussed how to use the Azure Cosmos DB Change Feed to build real-time applications. We covered the syntax, example, explanation, use, and important points of using the Change Feed. By understanding these concepts, you can leverage the Change Feed to build real-time applications that can react to real-time data changes.