MongoDB

MongoDB is easy to setup as a saga repository. MassTransit includes sensible defaults, and there is no need to explicitly map sagas.

Storing a saga in MongoDB requires an additional interface, ISagaVersion, which has a Version property used for optimistic concurrency. An example saga is shown below.

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

    public DateTime? OrderDate { get; set; }

    public int Version { get; set; }
}

Configuration

To configure MongoDB as a saga repository, 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 CorrelationId property will be automatically mapped to be the document identifier.

services.AddMassTransit(x =>
{
    x.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.

.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:

.MongoDbRepository(r =>
{
    r.Connection = "mongodb://127.0.0.1";
    r.DatabaseName = "orderdb";

    r.ClassMap(m => {});
});

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

class OrderStateClassMap :
    BsonClassMap<OrderState>
{
    public OrderStateClassMap()
    {
        MapProperty(x => x.OrderDate)
            .SetSerializer(new DateTimeSerializer(DateTimeKind.Utc));
    }
}

services.AddSingleton<BsonClassMap<OrderState>, OrderStateClassMap>();