Customize.md

Customize

When ever EventFlow doesn't meet your needs, e.g. if you want to collect statistics on each command execution time, you can customize EventFlow.

Basically EventFlow relies on an IoC container to allow developers to customize the different parts of EventFlow.

Note: Read the section "Changing IoC container" for details on how to change the IoC container used if you have specific needs like e.g. integrating EventFlow into an Owin application.

You have two options for when you want to customize EventFlow

• Decorate an implementation
• Replace an implementation

Decorating implementations

In the case of collecting statistics, you might want to wrap the existing ICommandBus with a decorator class the can collect statistics on command execution times.

void ConfigureEventFlow()
{
  var resolver = EventFlowOptions.new
    .RegisterServices(DecorateCommandBus)
    ...
    .CreateResolver();
}

void DecorateCommandBus(IServiceRegistration sr)
{
  sr.Decorate<ICommandBus>((r, cb) => new StatsCommandBus(sb));
}

class StatsCommandBus : ICommandBus
{
  private readonly _internalCommandBus;

  public StatsCommandBus(ICommandBus commandBus)
  {
    _internalCommandBus = commandBus;
  }

  // Here follow implementations of ICommandBus that call the
  // internal command bus and logs statistics
  ...
}

Registering new implementations

The more drastic step is to completely replace an implementation. For this you use the Register(...) and related methods on IServiceRegistration instead of the Decorate(...) method.

A example of a service that you might be interested in creating your own custom implementation of is IAggregateFactory which handles all aggregate creation, enabling you to pass additional services to a aggregate upon creation before events are applied.

Changing IoC container

EventFlow provides the NuGet package EventFlow.Autofac that allows you to set the internal ContainerBuilder used during EventFlow initialization.

Pass the ContainerBuilder to EventFlow and call CreateContainer() when configuration is done to create the container.

var containerBuilder = new ContainerBuilder();

var container = EventFlowOptions.With
  .UseAutofacContainerBuilder(containerBuilder) // Must be the first line!
  ...
  .CreateContainer();

Maybe call UseAutofacAggregateRootFactory() just before the CreateContainer() to use the Autofac aggregate root factory.