Azure Table Storage Configuration

Azure Tables are exposed in two ways in Azure - via Storage accounts & via the premium offering within Cosmos DB APIs. This persistence supports both implementations and behind the curtains uses the Azure.Data.Tables library for communication.

Note

Azure Tables currently only supports Optimistic Concurrency. Mass Transit manages the ETag property in Payload Context and uses this property for state machine updates. Concurrency errors can be spotted in logs via standard “Precondition Failed” errors from Table Storage.

Caution

Be sure to set DateTime properties as nullable when updated later in the saga. Failure to do this can result in 400 bad requests from Table Storage.

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

    public DateTime? OrderDate { get; set; }
}

Configure the saga repository

To configure a Table as the saga repository for a saga, use the code shown below using the AddMassTransit container extension.

TableClient cloudTable;
container.AddMassTransit(cfg =>
{
    cfg.AddSagaStateMachine<OrderStateMachine, OrderState>()
        .AzureTableRepository(endpointUri, key, r =>
        {
           cfg.ConnectionFactory(() => cloudTable);
        });
});

The container extension will register the saga repository in the container.

To configure the saga repository with a specific key formatter, use the code shown below with KeyFormatter configuration extension.

TableClient cloudTable;
container.AddMassTransit(cfg =>
{
    cfg.AddSagaStateMachine<OrderStateMachine, OrderState>()
        .AzureTableRepository(endpointUri, key, r =>
        {
           cfg.ConnectionFactory(() => cloudTable);
           cfg.KeyFormatter(() => new ConstRowSagaKeyFormatter<OrderState>(typeof(OrderState).Name)))
        });
});

Unlike the default ConstPartitionSagaKeyFormatter, ConstRowSagaKeyFormatter in this example uses PartitionKey to store the correlationId which may benefit from scale-out capability of Tables.