Petl

Petl is an Event Sourcing framework built to support CQRS architectures, specifically on Microsoft Orleans.

The Petl.EventSourcing library provides the base interfaces for implementing contracts related to Event Sourcing, such that developers may create provider specific implementations, such as Petl.EventSourcing.Providers.MongoDb

The Petl.EventSourcing.Orleans library offers an EventSourcedGrain that supports (will support) common scenarios related to Event Sourcing.

public sealed class AccountGrain : 
    EventSourcedGrain<BankAccount, BankAccountBaseEvent>,
    IAccountGrain
{
    public ValueTask<bool> Withdraw(double amount)
    {
        if (amount > State.Balance)
        {
            return ValueTask.FromResult(false);
        }

        Raise(new AmountWithdrawn { Amount = amount });

        return ValueTask.FromResult(true);
    }
}

Event and State are managed through a single interface, IEventLog<TView, TEntry>. The goal is to support the possibility to truncate the event log by snapshotting the view.

public interface IEventLog<TView, TEntry>
    where TView : class, new()
    where TEntry : class
{
    // ...
}

An instance of the event log is associated with every EventSourcedGrain, providing a window into the underlying data. The event log may load a snapshot and/or events to hydrate and maintain the state of the grain's data.

A MongoDB implementation is being provided with Petl.

public class MongoDbEventLog<TView, TEvent> : IEventLog<TView, TEvent>
    where TView : class, new()
    where TEvent : class
{
    // ...
}

To use the MongoDB provider, reference the appropriate libraries and configure the services in your Program.cs

await Host.CreateDefaultBuilder(args)
    .UseOrleans(silo =>
    {
        silo
            .ConfigureServices((services) =>
            {
                // configure the grain storage serializer as the event serializer
                services.AddOrleansEventSerializer();
                
                // add the mongo event log
                services.AddMongoEventSourcing("your-database");
            })
            .UseLocalhostClustering()
            .UseMongoDBClient(sp =>
                MongoClientSettings.FromConnectionString("mongodb://localhost:27017/")
            )
            .UseDashboard();
    })
    .RunConsoleAsync();