# Azure Service Bus Pub/Sub Native Integration

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This sample shows how to subscribe to events published by an NServiceBus endpoint using the Azure Service Bus API.

## Prerequisites

An environment variable named `AzureServiceBus_ConnectionString` with the connection string for the Azure Service Bus namespace.

## Code walk-through

The sample contains three executable projects:

* `Publisher`: an NServiceBus endpoint that publishes `EventOne` and `EventTwo` events.
* `NativeSubscriberA`: an executable subscribing to the `EventOne` event published by the `Publisher`.
* `NativeSubscriberB`: an executable subscribing to both events published by the `Publisher`.

## Running the sample

1. First, run the `Publisher` project by itself. This will create all the necessary publish/subscribe infrastructure in Azure Service Bus, including the default `bundle-1` topic.
2. Run the projects normally so that all endpoints start.
3. In the `Publisher` window, press any key to publish an event.
    * The endpoint in the `NativeSubscriberA` window will receive `EventOne`.
    * The endpoint in the `NativeSubscriberB` window will receive both `EventOne` and `EventTwo`.

## Setting up namespace entities

Each subscriber requires a topic subscription to receive the events published by the `Publisher`. The subscriptions are created on the `bundle-1` topic, which is [the default](/transports/azure-service-bus/configuration.md#entity-creation) name used by NServiceBus endpoints.

<!-- snippet: SubscriptionCreation -->

```cs
await client.CreateSubscriptionAsync(new CreateSubscriptionOptions(topicPath, subscriptionName)
{
    LockDuration = TimeSpan.FromMinutes(5),
    EnableDeadLetteringOnFilterEvaluationExceptions = false,
    MaxDeliveryCount = int.MaxValue,
    EnableBatchedOperations = true,
}, new CreateRuleOptions(ruleName, sqlFilter));
```

<!-- endsnippet -->

### Subscription filters

Subscriptions created by `NativeSubscriberA` and `NativeSubscriberB` contain a single filtering rule. `NativeSubscriberA` subscribes to the `EventOne` events only by specifying a SQL subscription rule (`event-one`) that matches the event type name stored in the event properties collection:

<!-- snippet: EventOneSubscription -->

```cs
await TopologyManager.CreateSubscription(
    ConnectionString,
    subscriptionName,
    ruleName: "event-one",
    sqlFilter: new SqlRuleFilter($"[NServiceBus.EnclosedMessageTypes] LIKE '%{typeof(EventOne).FullName}%'")
    );
```

<!-- endsnippet -->

The other subscriber uses [`TrueFilter`](https://learn.microsoft.com/en-us/dotnet/api/microsoft.servicebus.messaging.truefilter?view=azure-dotnet) in the `all-events` rule which ensures that both `EventOne` and `EventTwo` events are routed to its subscription.