Question

I’m trying to create a simple event store using C# and [ServiceStack] Redis.

public class AggregateEvents
{
    public Guid Id { get; set;}
    public List<DomainEvent> Events { get; set; }
}

public abstract class DomainEvent { }

public class UserRegisteredEvent : DomainEvent 
{
    public Guid UserId { get; set; }
    public string Name { get; set; }
}

public class UserPromotedEvent : DomainEvent
{
    public Guid UserId { get; set; }
    public string NewRole { get; set; }
}

if I do a roots.GetAll() I get an exception because the abstract class could not be instantiated. If I turn the base class into an interface instead, the Events object is null and the objects I stored in there get lost.

Any thoughts?

Edit 1

No joy using v3.03 and this code:

    [Test]
    public void foo()
    {
        var client = new RedisClient("localhost");
        var users = client.GetTypedClient<AggregateEvents>();


        var userId = Guid.NewGuid();

        var eventsForUser = new AggregateEvents
                       {
                           Id = userId,
                           Events = new List<DomainEvent>()
                       };

        eventsForUser.Events.Add(new UserPromotedEvent { UserId = userId });


        users.Store(eventsForUser);

        var all = users.GetAll(); // exception
    }

Edit 2

Also not worked with this approach;

    [Test]
    public void foo()
    {
        var userId = Guid.NewGuid();
        var client = new RedisClient("localhost");

        client.As<DomainEvent>().Lists["urn:domainevents-" + userId].Add(new UserPromotedEvent {UserId= userId});


        var users = client.As<DomainEvent>().Lists["urn:domainevents-" + userId];

        foreach (var domainEvent in users) // exception
        {

        }
    }

Answer 1

Can you try again with the latest version (v3.05+) of the ServiceStack Redis client:

https://github.com/ServiceStack/ServiceStack.Redis/downloads

The ServiceStack Json Serializer which the client uses has just added support for deserialization of Abstract/interface types which will be in the latest version of the client.

Note: this works by embedding __type information into the JSON payload which tells the serializer what concrete class it should deserialize into. It only embeds this information for Abstract/interface/object types. So you when you serialize you will need to cast to the abstract type, e.g:

redis.Store((DomainEvent)userPromoEvent);

or if adding to a list:

redis.As<DomainEvent>().Lists["urn:domainevents"].Add(userPromoEvent);

These examples now work as indicated by the newly added DomainEvents Unit Tests 🙂

[Test]
public void Can_Retrieve_DomainEvents()
{
    var userId = Guid.NewGuid();
    var client = new RedisClient("localhost");
    client.FlushAll();

    client.As<DomainEvent>().Lists["urn:domainevents-" + userId].Add(
        new UserPromotedEvent { UserId = userId });

    var users = client.As<DomainEvent>().Lists["urn:domainevents-" + userId];

    Assert.That(users.Count, Is.EqualTo(1));

    var userPromoEvent = (UserPromotedEvent)users[0];
    Assert.That(userPromoEvent.UserId, Is.EqualTo(userId));
}


[Test]
public void Can_from_Retrieve_DomainEvents_list()
{
    var client = new RedisClient("localhost");
    var users = client.As<AggregateEvents>();

    var userId = Guid.NewGuid();

    var eventsForUser = new AggregateEvents
    {
        Id = userId,
        Events = new List<DomainEvent>()
    };

    eventsForUser.Events.Add(new UserPromotedEvent { UserId = userId });

    users.Store(eventsForUser);

    var all = users.GetAll(); 
}