Implement the change feed processor

5 minutes

The change feed processor is created in a few steps:

Get the processor builder from the monitored (source) container variable
Use the builder to build-out the processor by specifying the delegate, processor name, lease container, and host instance name
Start the processor

First, you should create an instance of Microsoft.Azure.Cosmos.Container for both the source and lease container.

Container sourceContainer = client.GetContainer("cosmicworks", "products");

Container leaseContainer = client.GetContainer("cosmicworks", "productslease");

Next, you can use the GetChangeFeedProcessorBuilder method from a container instance to create a builder. At this point, you should specify the name of the processor and the delegate to handle each batch of changes.

var builder = sourceContainer.GetChangeFeedProcessorBuilder<Product>(
    processorName: "productItemProcessor",
    onChangesDelegate: changeHandlerDelegate
);

The builder ships with a series of fluent methods to configure the processor that includes, but is not limited to:

Method	Description
WithInstanceName	Name of host instance
WithStartTime	Set the pointer (in time) to start looking for changes after
WithLeaseContainer	Configures the lease container
WithErrorNotification	Assigns a delegate to handle errors during execution
WithMaxItems	Quantifies the max number of items in each batch
WithPollInterval	Sets the delay when the processor will poll the change feed for new changes

A simple example would be to configure the instance name using WithInstanceName, the lease container using WithLeaseContainer, and then Build the change feed processor.

ChangeFeedProcessor processor = builder
    .WithInstanceName("desktopApplication")
    .WithLeaseContainer(leaseContainer)
    .Build();

The resulting change feed processor includes both StartAsync and StopAsync methods to run and terminate the processor asynchronously.

await processor.StartAsync();

// Wait while processor handles items

await processor.StopAsync();

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