Aggregate

public class Concert : AggregateRoot<ConcertState>
{
    Concert() {} // keep the private parameterless constructor
    
    public Concert(string name, Venue venue, DateTimeOffset startTime, TimeSpan duration)
    {
        // business logic for creating a concert
        Apply(new ConcertAnnounced(...));
    }

    public void RegisterPerformer(Performer performer)
    {
        // business logic for registering a performer
        Apply(new PerformerRegistered(...));
    }
    
    // ...
}

public class ConcertState : AggregateRootState<Concert, ConcertId>
{
    public ConcertState()
    {
        Performers = new List<Performer>();
    }

    public override ConcertId Id { get; set; }

    public string Name { get; private set; }

    public Venue Venue { get; private set; }

    public DateTimeOffset StartTime { get; private set; }

    public TimeSpan Duration { get; private set; }

    public List<Performer> Performers { get; private set; }
    
    public void When(ConcertAnnounced @event)
    {
        // change the state here ...
    }
    
    public void When(PerformerRegistered @event)
    {
        // change the state here ...
    }
}

[DataContract(Name = "e96d90d0-4943-43f4-8a84-cd90b1217d06")]
public class ConcertId : AggregateRootId
{
    const string RootName = "concert";

    public ConcertId(AggregateUrn urn) : base(RootName, urn) { }
    public ConcertId(string idBase, string tenant) : base(idBase, RootName, tenant) { }
    protected ConcertId() { }
}

[DataContract(Name = "e96d90d0-4943-43f4-8a84-cd90b1217d06")]
public class ConcertId : AggregateRootId<ConcertId>
{
    const string RootName = "concert";

    ConcertId() { }
    public ConcertId(string id, string tenant) : base(id, RootName, tenant) { }

    protected override ConcertId Construct(string id, string tenant)
    {
        return new ConcertId(id, tenant);
    }
}