pekalam / chronicle

Implementation of saga pattern for .NET Core

Chronicle

Chronicle is simple process manager/saga pattern implementation for .NET Core that helps you manage long-living and distributed transactions.

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Installation

Chronicle is available on NuGet

Package manager

Install-Package Chronicle_ -Version 3.2.1

.NET CLI

dotnet add package Chronicle_ --version 3.2.1

Getting started

In order to create and process a saga you need to go through a few steps:

1. Create a class that derives from either Saga or Saga<TData>.
2. Inside your saga implementation, inherit from one or several ISagaStartAction<TMessage> and ISagaAction<TMessage> to implement HandleAsync() and CompensateAsync() methods for each message type. An initial step must be implemented as an ISagaStartAction<TMessage>, while the rest can be ISagaAction<TMessage>. It's worth mentioning that you can implement as many ISagaStartAction<TMessage> as you want. In this case, the first incoming message is going to initialize the saga and any subsequent ISagaStartAction<TMessage> or ISagaAction<TMessage> will only update the current saga state.
3. Register all your sagas in Startup.cs by calling services.AddChronicle(). By default, AddChronicle() will use the InMemorySagaStateRepository and InMemorySagaLog for maintaining SagaState and for logging SagaLogData in the SagaLog. The SagaLog maintains a historical record of which message handlers have been executed. Optionally, AddChronicle() accepts an Action<ChronicleBuilder> parameter which provides access to UseSagaStateRepository<ISagaStateRepository>() and UseSagaLog<ISagaLog>() for custom implementations of ISagaStateRepository and ISagaLog. If either method is called, then both methods need to be called.
4. Inject ISagaCoordinator and invoke ProcessAsync() methods passing a message. The coordinator will take care of everything by looking for all implemented sagas that can handle a given message.
5. To complete a successful saga, call CompleteSaga() or CompleteSagaAsync(). This will update the SagaState to Completed. To flag a saga which has failed or been rejected, call the Reject() or RejectAsync() methods to update the SagaState to Rejected. Doing so will utilize the SagaLog to call each message type's CompensateAsync() in the reverse order of their respective HandleAsync() method was called. Additionally, an unhanded exception thrown from a HandleAsync() method will cause Reject() to be called and begin the compensation.

Below is the very simple example of saga that completes once both messages (Message1 and Message2) are received:

public class Message1
{
    public string Text { get; set; }
}

public class Message2
{
    public string Text { get; set; }
}

public class SagaData
{
    public bool IsMessage1Received { get; set; }
    public bool IsMessage2Received { get; set; }
}

public class SampleSaga : Saga<SagaData>, ISagaStartAction<Message1>, ISagaAction<Message2>
{
    public Task HandleAsync(Message1 message, ISagaContext context)
    {
        Data.IsMessage1Received = true;
        Console.WriteLine($"Received message1 with message: {message.Text}");
        CompleteSaga();
        return Task.CompletedTask;
    }
    
    public Task HandleAsync(Message2 message, ISagaContext context)
    {
        Data.IsMessage2Received = true;
        Console.WriteLine($"Received message2 with message: {message.Text}");
        CompleteSaga();
        return Task.CompletedTask;
    }

    public Task CompensateAsync(Message1 message, ISagaContext context)
        => Task.CompletedTask;

    public Task CompensateAsync(Message2 message, ISagaContext context)
        => Task.CompletedTask;

    private void CompleteSaga()
    {
        if(Data.IsMessage1Received && Data.IsMessage2Received)
        {
            Complete();
            Console.WriteLine("SAGA COMPLETED");
        }
    }
}

Both messages are processed by mentioned coordinator:

var coordinator = app.ApplicationServices.GetService<ISagaCoordinator>();

var context = SagaContext
    .Create()
    .WithCorrelationId(Guid.NewGuid())
    .Build();

coordinator.ProcessAsync(new Message1 { Text = "Hello" }, context);
coordinator.ProcessAsync(new Message2 { Text = "World" }, context);

The result looks as follows:

Documentation

If you're looking for documentation, you can find it here.

Icon

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