public async Task <IEnumerable <IEvent> > Process <TCommand>(TCommand command)
where TCommand : class, ICommand
{
Argument.IsNotNull(command, nameof(command));
string aggregateId = command.GetAggregateId();
TAggregate aggregate = await _aggregateRepository.LoadById(aggregateId);
aggregate.Perform(command);
await _aggregateRepository.Save(aggregate);
return(aggregate.Changes);
}