How to parse back data from EventStore stream to correct type?

Question

I stored the event data in EventStore:

var data = new EventData(Guid.NewGuid(),
                         @event.GetType().ToString(),
                         true,
                         @event.ToJsonBytes(), 
                         @event.GetType().ToJsonBytes());

this.connection.AppendToStreamAsync(this.stream + "/" + aggregateId, 
                                    ExpectedVersion.Any, data);

Seems to work. But how to parse back the data from EventStore without giving the concrete type?

I tried this way, but this only parses the data for the base class:

foreach (var data in result.Events)
{
   var @event = data.Event.Data.ParseJson<Event>();
   if (@event != null) // event contains only the base type data
   {
      events.Add(@event);
   }
}

How to get back the data for SomeSpecialEvent that is derived from Event? There are several Event types and I can't put all in here (storage mechanism should be unaware of the concrete type).

Any ideas how to put the T into the .ParseJson without using generics?

Answer 1

Found a solution by myself:

        var result = this.connection.ReadStreamEventsForwardAsync(this.stream + "/" + aggregateId, 0, 4095, false).Result;

        foreach (var data in result.Events)
        {
            var assemblyQualifiedName = data.Event.Metadata.ParseJson<string>();
            var type = Type.GetType(assemblyQualifiedName);
            var json = Helper.UTF8NoBom.GetString(data.Event.Data);
            var @event = JsonConvert.DeserializeObject(json, type) as Event;
            if (@event != null)
            {
                events.Add(@event);
            }
        }

You need to add the type into metadata when saving:

           var type = @event.GetType().AssemblyQualifiedName;

            var data = new EventData(
                Guid.NewGuid(),
                @event.GetType().Name,
                true,
                @event.ToJsonBytes(),
                type.ToJsonBytes());