Domain Events

OrigoDB domain events are an effort to support event driven, reactive designs. Capture domain events to trigger additional external behavior like sending emails, updating read models, sending messages, relaying through web sockets, etc.

Publish events by adding to the List Execution.Current.Events.

Zero or more events are produced during command execution. The events are collected by the Engine and included in the EventArgs when the Engine.CommandExecuted event fires. If a command fails or is aborted, no events are published.

Modeling domain events

An event is an object representing something that has happened in the past.
The event name should be a verb in the past tense
Events should be immutable
Events must not expose mutable references to objects within the model
Events must implement the empty IEvent marker interface
Mark events Serializable

An example event

[Serializable]
public class CustomerAdded : IEvent
{
   public int readonly CustomerId;

   public CustomerAdded(int id)
   {
      CustomerId = id;
   }
}

Producing events

Emit events by adding them to the current execution context.

[Serializable]
public class CreateCustomerCommand : Command<MyModel>
{
   public int Id{get;set;}
   public string Name{get;set;}

   public override void Execute(MyModel db)
   {
      var customer = new Customer(Id, Name);
      db.Customers.Add(customer);
      var ctx = Execution.Current;
      ctx.Events.Add(new CustomerCreated(Id));
   }
}

Consuming events

Subscribe to domain events through Engine.CommandExecuted:

var engine = Engine.For<MyModel>();
engine.CommandExecuted += (s,e) => {
   foreach(IEvent evt in e.Events)
   {
      Console.WriteLine("Domain Event: " + evt);
   }
};

//execute command which produces events
engine.Execute(new CreateCustomerCommand(42, "Batman"));