EventSaucing

EventSaucing

Add a little EventSauce to your project ;)

This library brings together different stacks to create an Event Sourcing solution.

Reading list before using the project:

• Dapper
• Event Sourcing design

Installing

The latest release of EventSaucing is available on NuGet.

Usage

Once referenced in your project you need to configure it in your Startup inside ConfigureServices.

var builder = new ContainerBuilder();

builder.RegisterEventSaucingModules(new EventSaucingConfiguration {
   ConnectionString = // Set your connection string
});

builder.Populate(services); // Populate your services.

var container = builder.Build();

container.StartEventSaucing(); // Start EventSaucing

You can then construct your Aggregates by inheriting from the Aggregate class and including Apply() methods to handle the raised events on the aggregate.

public class FooAggregate : Aggregate {
  public FooAggregate(Guid id) {
    base.Id = id;
  }

  public int Bar { get; set; }

  public void Create(int bar) {
    RaiseEvent(new FooCreated(bar));
  }

  void Apply(FooCreated @event) {			
    Bar = @event.Bar;
  }
}
// A POCO for the event state
public class FooCreated {
  public FooCreated(int bar) {
    Bar = bar;
  }
  public int Bar { get; }
}

You can then create Projectors by inheriting from ProjectorBase and setting up which events to handle. You must also give each projector a unique number. In this example Dapper is used to interact with the persistence store.

[Projector(1)] // The unique projector id.
public class FooProjector: ProjectorBase {
  readonly ConventionBasedCommitProjecter _conventionProjector;

  public FooProjector(IDbService dbService, IPersistStreams persistStreams):base(persistStreams, dbService) {
    var conventionalDispatcher = new ConventionBasedEventDispatcher(c => Checkpoint = c.ToSome())
      .FirstProject<FooCreated>(OnFooCreated)
      .ThenProject<SomeEvent>(OnSomeEventHandler);

    _conventionProjector = new ConventionBasedCommitProjecter(this, dbService, conventionalDispatcher);
  }

  public override void Project(ICommit commit) {
    _conventionProjector.Project(commit);
  }

  private void OnFooCreated(IDbTransaction tx, ICommit commit, FooCreated @event) {
    var sqlParams = new { 
      Id = commit.AggregateId(), 
      Bar = FooCreated.Bar 
    };

    const string sql = @"
      INSERT INTO [dbo].[FooProjector.Foo]
        ([Id]
        ,[Bar])
      SELECT
        @Id
        ,@Bar
      WHERE NOT EXISTS(SELECT * FROM [dbo].[FooProjector.Foo] WHERE Id = @Id);";
    tx.Connection.Execute(sql, (object)sqlParams, tx);
  }

Dependencies

• Dapper - Used to interact with the sql persistence store.
• NEventStore - Used for storage of the event stream.
• Serilog - Used for logging.
• Akka.NET - Used to deliver deliver events to aggregates & projectors.
• Autofac - Used for dependency injection.
• Scalesque - Used to add functional programming in c#.