Marten

Package: MassTransit.Marten

Marten is an open source library that provides provides .NET developers with the ability to easily use the proven PostgreSQL database engine and its fantastic JSON support as a fully fledged document database. To use Marten and PostgreSQL as saga persistence, you need to install MassTransit.Marten NuGet package and add some code.

MassTransit will automatically configure the CorrelationId property so that Marten will use that property as the primary key. No attribute is necessary.

public class OrderState :
    SagaStateMachineInstance
{
    public Guid CorrelationId { get; set; }
    public string CurrentState { get; set; }

    public DateTime? OrderDate { get; set; }
}

Container Integration

To configure Marten as the saga repository for a saga, use the code shown below using the AddMassTransit container extension. This will configure Marten to connect to the local Marten instance on the default port using Optimistic concurrency.

container.AddMassTransit(cfg =>
{
    var connectionString = "server=localhost;port=5432;database=orders;user id=web;password=webpw;";

    cfg.AddSagaStateMachine<OrderStateMachine, OrderState>()
        .MartenRepository(connectionString);
});

Optimistic Concurrency

To use Marten's built-in Optimistic concurrency, use the configuration options to configure the schema. Marten supports optimistic concurrency by using an eTag-like version field in the metadata, which does not require any additional fields in the saga class.

container.AddMassTransit(cfg =>
{
    var connectionString = "server=localhost;port=5432;database=orders;user id=web;password=webpw;";

    cfg.AddSagaStateMachine<OrderStateMachine, OrderState>()
        .MartenRepository(connectionString, r =>
        {
            r.Schema.For<OrderState>().UseOptimisticConcurrency(true);
        });
});

Alternatively, you can add the UseOptimisticConcurrency attribute to the class.

[UseOptimisticConcurrency]
public class OrderState :
    SagaStateMachineInstance
{
    public Guid CorrelationId { get; set; }
    // ...
}

Index Creation

Marten can create indices for properties, which greatly increases query performance. If your saga is correlating events using other fields, index creation is recommended. For example, if an OrderNumber property was added to the OrderState class, it could be indexed by configuring it in the repository.

public class OrderState :
    SagaStateMachineInstance
{
    public Guid CorrelationId { get; set; }
    public string CurrentState { get; set; }

    public string OrderNumber { get; set; }

    public DateTime? OrderDate { get; set; }
}

container.AddMassTransit(cfg =>
{
    var connectionString = "server=localhost;port=5432;database=orders;user id=web;password=webpw;";

    cfg.AddSagaStateMachine<OrderStateMachine, OrderState>()
        .MartenRepository(connectionString, r =>
        {
            r.Schema.For<OrderState>().Index(x => x.OrderNumber);
        });
});

Details on how Marten creates indices is available in the Computed Index documentation.