Event Dispatcher Entity Framework Core

Entity Framework Core Domain and Integration event dispatch.

Quick start

1. Construct a EntityFrameworkEventDispatcherContext class by passing in the DbContext itself, and an implementation of IEventDispatcher.

2. Override the following SaveChanges() and SaveChangesAsync() methods with the example code below (or roll your own).

3. Include the ClearEvents() and GetEventDispatcherContext() methods if required.

public override int SaveChanges(bool acceptAllChangesOnSuccess)
    {
        IEventDispatcherContext dispatcherContext = GetEventDispatcherContext();
        DispatchEvents<IDomainEvent>(dispatcherContext);
        int returnCode = base.SaveChanges(acceptAllChangesOnSuccess);
        DispatchEvents<IIntegrationEvent>(dispatcherContext);
        ClearEvents();
        return returnCode;
    }

public override async Task<int> SaveChangesAsync(bool acceptAllChangesOnSuccess, CancellationToken cancellationToken = default(CancellationToken))
{
    IEventDispatcherContext dispatcherContext = GetEventDispatcherContext();
    await dispatcherContext.DispatchAsync<IDomainEvent>(dispatcherContext, cancellationToken).ConfigureAwait(false);
    int returnCode = await base.SaveChangesAsync(acceptAllChangesOnSuccess, cancellationToken).ConfigureAwait(false);
    await dispatcherContext.DispatchAsync<IIntegrationEvent>(dispatcherContext, cancellationToken).ConfigureAwait(false);
    ClearEvents();
    return returnCode;
}

private void ClearEvents()
{
    foreach (EntityEntry<IEventObject> eventObject in this.ChangeTracker.Entries<IEventObject>())
    {
        eventObject.Entity.EventStore.ClearEvents();
    }
}
    
private IEventDispatcherContext GetEventDispatcherContext()
{
    return new EntityFrameworkEventDispatcherContext(this, this.GetService<IEventDispatcher>());
}

4. Add the IEventObject interface to any of your DbContext entities.
   • This will require you to implement the IEventStore interface.
   • The following example will demonstrate.

public class User : IEntity
{
    public User()
    {
        EventStore = new EventStore();
    }

    public IEventStore EventStore { get; }
}

5. To add a domain event, create a class which derives from IDomainEvent and you can add that to your eventstore on the entity.
   • Integration events should follow IIntegrationEvent.
   • You can create your own event types and use them as you wish. Dispatch them at your chosen point in the SaveChanges() or SaveChangesAsync() methods.

• When save changes is called any event dispatch handlers registered will handle that event.

• Your handlers should derive from the following interface to picked up by the IEventDispatcher:

  • IEventDispatchHandler<MyDomainEvent>

• See the link to a sample project below, which should demonstrate clearly.

Samples

See https://github.com/TheDanielDoyle/EventDispatcher.EntityFrameworkCore/blob/develop/Samples/EventDispatcher.EntityFrameworkCore.Samples.InMemory/SampleDbContext.cs for an example DbContext implementation, which uses the EntityFrameworkEventDispatcherContext.