NBB.Data.EventSourcing

NBB.Data.EventSourcing

This package aims to help you deal with data access when working with event sourced domain models.

NuGet install

dotnet add package NBB.Data.EventSourcing

Philosophy

It offers an EventSourcedRepository that:

• reads/persists events from/into an IEventStore
• manages snapshots using an ISnapshotStore
• dispatches events using MediatR

EventSourcedRepository offers two operations needed when working with ES domains:

public interface IEventSourcedRepository<TAggregateRoot>
        where TAggregateRoot : IEventSourcedAggregateRoot, new()
{
    Task SaveAsync(TAggregateRoot aggregate, CancellationToken cancellationToken = default(CancellationToken));
    Task<TAggregateRoot> GetByIdAsync(object id, CancellationToken cancellationToken = default(CancellationToken));
}

For EventSore and SnapshotStore configuration see NBB.EventStore.

For more info about how to model event sourced snapshot-able entities see NBB.Domain.

Loading domain aggregates

When loading domain aggregates, the repository uses the following algorithm:

• if the entity is snapshot-able it tries to load the last snapshot
• it loads the events from the event store (starting with last one from the snapshot, if any)
• it applies the events, re-hydrating the state of the aggregate, by calling the LoadFromHistory instance method on the ES aggregate root

Saving domain aggregates

When saving domain aggregates, the repository uses the following algorithm:

• fetches uncommitted events from the aggregate
• saves the events in the event store, with the concurrency control set to aggregate-loaded-at-version
• if the entity is snapshot-able it checks if it should persist a snapshot
• dispatches events using MediatR

Stream identity

The process of mapping an event sourced entity to a stream, is a pure function like this:

 public static string GetStream(this IIdentifiedEntity entity)
    => entity.GetType().FullName + ":" + entity.GetIdentityValue();

Container registration

You can register custom options for ES data access like this:

services.AddEventSourcingDataAccess((sp, builder)=>builder.Options.DefaultSnapshotVersionFrequency = 5)

Register an ES repository for an aggregate like so:

services.AddEventSourcedRepository<Contract>();

Sample usage

For a working sample see: NBB.Contracts sample