In order to use the transactional session feature with CosmosDB Persistence, add a reference to the NServiceBus. NuGet package.
Configuration
To enable the transactional session feature:
var persistence = config.UsePersistence<CosmosPersistence>();
persistence.EnableTransactionalSession();
Opening a session
To open a CosmosDB transactional session, a partition key must be provided:
using var childScope = serviceProvider.CreateScope();
var session = childScope.ServiceProvider.GetService<ITransactionalSession>();
await session.Open(
new CosmosOpenSessionOptions(
new PartitionKey("MyPartitionKey")));
// use the session
await session.Commit();
Custom container
By default, the transactional session uses the configured default container. The CosmosOpenSessionOptions instance can be configured with container information to be used for this transaction:
using var childScope = serviceProvider.CreateScope();
var session = childScope.ServiceProvider.GetService<ITransactionalSession>();
await session.Open(
new CosmosOpenSessionOptions(
new PartitionKey("MyPartitionKey"),
new ContainerInformation(
"MyContainer",
new PartitionKeyPath("/path/to/partition/key"))));
// use the session
await session.Commit();
Transaction usage
Message and database operations made via the the transactional session are committed together once the session is committed:
await session.Open(
new CosmosOpenSessionOptions(
new PartitionKey("MyPartitionKey")));
// add messages to the transaction:
await session.Send(new MyMessage());
// access the database:
var cosmosSession = session.SynchronizedStorageSession.CosmosPersistenceSession();
await session.Commit();
See the Cosmos DB persistence transactions documentation for further details about using the transaction.
In order to guarantee atomic consistency across message and database operations, the outbox must be enabled. Otherwise Commit executes database modifications first and then messages are dispatched with best-effort.