Enforce referential integrity by using Change Feed and Azure Functions

Enforcing referential integrity is a critical aspect of maintaining data consistency in any database system. Azure Cosmos DB, a globally distributed, multi-model database service provided by Microsoft Azure, offers several mechanisms to achieve referential integrity. One powerful approach is to leverage Change Feed and Azure Functions together. In this article, we will explore how to enforce referential integrity using Change Feed and Azure Functions in Azure Cosmos DB.

Understanding Referential Integrity

Referential integrity ensures that relationships between data entities are maintained, preventing orphaned or inconsistent data entries. By using Change Feed and Azure Functions, we can automatically react to changes in the database and enforce referential integrity in near real-time.

Change Feed and Azure Functions

Change Feed is a feature in Azure Cosmos DB that provides an ordered, immutable stream of database changes. Whenever a document is inserted, updated, or deleted, the Change Feed captures those modifications. Azure Functions, on the other hand, is a serverless compute service that allows you to respond to events and triggers in various Azure services.

Implementing Referential Integrity

To enforce referential integrity, we can set up an Azure Function that subscribes to the Change Feed and performs the necessary checks and actions whenever a change occurs.

Step 1: Create an Azure Function

Start by creating a new Azure Function with an HTTP trigger. This trigger will be used to initialize the Change Feed processor.

class CustomerOrderIntegrityFunction

Step 2: Configure Cosmos DB Trigger

Add a Cosmos DB trigger to the Function. This trigger will be set up to monitor the “Orders” collection for changes.

[CosmosDBTrigger("databaseId", "collectionId", ConnectionStringSetting = "cosmosDbConnectionString", LeaseCollectionName = "leases")]

Step 3: Read the Change Feed

Inside the Function’s code, retrieve the modified order document from the Change Feed.

async Task Run([CosmosDBTrigger("databaseId", "collectionId", ConnectionStringSetting = "cosmosDbConnectionString", LeaseCollectionName = "leases")] IReadOnlyList input, ILogger log)


Step 4: Retrieve Customer Document

Based on the “customerId” field within the order document, query the “Customers” collection to verify the existence of the referenced customer.

Uri collectionUri = UriFactory.CreateDocumentCollectionUri(databaseId, "customers");
var customer = client.CreateDocumentQuery(collectionUri)
.Where(c => c.Id == order.CustomerId)
.AsEnumerable()
.FirstOrDefault();


Step 5: Enforce Referential Integrity

If the customer does not exist, take the necessary action to maintain referential integrity. This could involve deleting the order, updating the “customerId” field, or sending a notification.

if (customer == null)
{
// Perform action to maintain referential integrity
}

Step 6: Deploy Azure Function

Publish the Azure Function to Azure for execution.

Step 7: Configure Change Feed Processor

Once the Azure Function is deployed, configure the Change Feed processor to start processing changes from the “Orders” collection.

await host.StartAsync();

By following these steps, you can enforce referential integrity between the “Orders” and “Customers” collections in Azure Cosmos DB. As new orders are added or modified, the Azure Function will automatically verify the existence of referenced customers and take appropriate action if necessary.

Enforcing referential integrity is essential for maintaining data consistency in any database system. Azure Cosmos DB, along with Change Feed and Azure Functions, offers a powerful mechanism to achieve this goal. By automatically reacting to changes in the database, you can ensure that data relationships are maintained, avoiding orphaned or inconsistent entries.