MongoDB

MongoDB is an easy to use saga repository, because setup is easy. There is no need for class mapping, the saga instances can be persisted easily using a MongoDB collection.

To use MongoDB, an additional interface, property, and data annotation are required on saga instances. The interface, IVersionedSaga, contains a Version property that is used to support optimistic concurrency versioning. The annotation [BsonId] configures the CorrelationId property as the id property in MongoDB.

public class OrderState :
    SagaStateMachineInstance,
    IVersionedSaga
{
    [BsonId]
    public Guid CorrelationId { get; set; }
    public string CurrentState { get; set; }

    public DateTime? OrderDate { get; set; }

    public int Version { get; set; }
}

Container Integration

To configure MongoDB as the saga repository for a saga, use the code shown below using the AddMassTransit container extension. This will configure MongoDB to connect to the local MongoDB instance on the default port using Optimistic concurrency. The annotation [BsonId] is redundant, CorrelationId property will be automatically mapped.

container.AddMassTransit(cfg =>
{
    cfg.AddSagaStateMachine<OrderStateMachine, OrderState>()
        .MongoDbRepository(r =>
        {
            r.Connection = "mongodb://127.0.0.1";
            r.DatabaseName = "orderdb";
        });
});

In the example above, saga instances are stored in a collection named order.states. The collection name can be specified using the CollectionName property. Alternatively, a collection name formatter can be specified using the CollectionNameFormatter method.

container.AddMassTransit(cfg =>
{
    cfg.AddSagaStateMachine<OrderStateMachine, OrderState>()
        .MongoDbRepository(r =>
        {
            r.Connection = "mongodb://127.0.0.1";
            r.DatabaseName = "orderdb";

            r.CollectionName = "orders";
        });
});

Container integration gives you ability to configure class map based on saga type. You can use Action<BsonClassMap> explicitly:

container.AddMassTransit(cfg =>
{
    cfg.AddSagaStateMachine<OrderStateMachine, OrderState>()
        .MongoDbRepository(r =>
        {
            r.Connection = "mongodb://127.0.0.1";
            r.DatabaseName = "orderdb";

            r.ClassMap(cfg => {/*Your configuration*/})
        });
});

BsonClassMap<TSaga> registered inside container will be used by default for TSaga configuration:

class OrderStateClassMap : BsonClassMap<OrderState>
{
  	public OrderStateClassMap()
    {
      	AutoMap();
      	/*
      	Your other configuration
      	*/
    }
}

container.AddSingleton<BsonClassMap<OrderState>>(new OrderStateClassMap());

container.AddMassTransit(cfg =>
{
    cfg.AddSagaStateMachine<OrderStateMachine, OrderState>()
        .MongoDbRepository(r =>
        {
            r.Connection = "mongodb://127.0.0.1";
            r.DatabaseName = "orderdb";
        });
});