Implement referential enforcement by using a change feed

In this article, we will explore how to implement referential enforcement using a change feed in the context of designing and implementing native applications using Microsoft Azure Cosmos DB. Referential enforcement ensures that referential integrity is maintained between different entities in a database, allowing for consistent and reliable data access and manipulation.

Azure Cosmos DB Overview

Azure Cosmos DB is a globally distributed, multi-model database service provided by Microsoft. It offers consistent low latency and high throughput, making it an ideal choice for building scalable and highly available applications. With its native support for multiple data models, including key-value, document, graph, and columnar, Azure Cosmos DB provides flexibility in data modeling and querying.

The Change Feed Feature

One of the key features of Azure Cosmos DB is the change feed. The change feed provides an ordered, distributed, and durable stream of changes made to documents in a collection. It enables developers to build reactive and event-driven applications by listening to changes in the data and taking action based on those changes.

Steps to Implement Referential Enforcement Using a Change Feed

1. Create the necessary collections: Start by creating collections for the entities that need to have referential integrity enforced. For example, if you have a “Customers” collection and an “Orders” collection, you would create these collections in Azure Cosmos DB.
2. Define the document schema: Define the document schema for each collection, specifying the properties and their data types. For example, a customer document may have properties such as CustomerId, Name, and Email, while an order document may have properties such as OrderId, CustomerId, and Product.
3. Enable the change feed: Enable the change feed for the collections that need referential enforcement. This can be done through the Azure Cosmos DB management portal or programmatically using the Azure Cosmos DB SDKs. Once enabled, the change feed will start capturing the changes made to the documents in the collection.
4. Implement change feed processing: Implement code to process the change feed and perform referential enforcement. This can be done using Azure Functions, Azure Logic Apps, or any other event-driven processing mechanism. When a change occurs in the collection, the change feed will trigger the processing code, allowing you to take action based on the change. In the case of referential enforcement, you can check if the referenced entities exist before allowing the change to be applied.

Example: Change Feed Processing Using Azure Functions and Azure Cosmos DB SDK for .NET

Below is an example demonstrating how to implement change feed processing using Azure Functions and the Azure Cosmos DB SDK for .NET:

public static async Task Run([CosmosDBTrigger(
databaseName: "YourDatabase",
collectionName: "YourCollection",
ConnectionStringSetting = "CosmosDBConnection",
LeaseCollectionName = "YourLeaseCollection")]IReadOnlyList documents,
ILogger log)
{
// Process the changed documents
foreach (var document in documents)
{
if (document.GetPropertyValue("EntityType") == "Order")
{
// Perform referential enforcement for orders
var customerId = document.GetPropertyValue("CustomerId");
if (!await CheckCustomerExists(customerId))
{
log.LogError($"Customer {customerId} not found. Order enforcement failed.");
// Additional error handling logic
}
}
}
}

private static async Task CheckCustomerExists(string customerId)
{
// Check if the customer exists in the Customers collection
// Implement your custom logic here based on your data access layer
// Return true if the customer exists, otherwise false
}


In the above example, the Azure Functions trigger is configured to listen to changes in the “YourCollection” collection. When a change occurs, the function processes the changed documents and performs referential enforcement for orders. It checks if the referenced customer exists in the “Customers” collection using the “CheckCustomerExists” method and handles any errors accordingly.

By implementing referential enforcement using a change feed in Azure Cosmos DB, you can ensure the integrity of your data and maintain consistency between related entities. This allows for reliable and accurate data access and manipulation in your native applications.