public async Task <bool> MoveNextAsync()
{
if (_buffer.Count > 0)
{
_buffer.Dequeue();
if (_buffer.Count > 0)
{
return(true);
}
}
if (_isEndOfStream)
{
return(false);
}
// Why the 'while'? If the stream was soft-deleted in the past it starts at an event with number != 0.
// So the first read operation returns 0 events, but reports the actual start position of the stream
// (currentSlice.NextEventNumber). Then, a second read is required to actually read the first few events.
while (_buffer.Count == 0 && !_isEndOfStream)
{
var currentSlice = await _connection.ReadStreamEventsForwardAsync(_streamName, _startPosition, PageSize, false);
foreach (var eventData in currentSlice.Events)
{
try
{
var ev = eventData.Event.ToIEvent().MigrateToLatestVersion();
_buffer.Enqueue(ev);
}
catch (ArgumentException e)
{
EventParsingFailed?.Invoke(this, new EventParsingFailedArgs(eventData, e));
}
}
_startPosition = currentSlice.NextEventNumber;
_isEndOfStream = currentSlice.IsEndOfStream;
}
return(_buffer.Count > 0);
}
private Task OnEventAppeared(EventStoreCatchUpSubscription _, ResolvedEvent resolvedEvent)
{
try
{
// Note regarding migration:
// Event types may change over time (properties get added/removed etc.)
// Whenever an event has multiple versions, an event of an obsolete type should be transformed to an event
// of the latest version, so that ApplyEvent(...) only has to deal with events of the current version.
var ev = resolvedEvent.Event.ToIEvent().MigrateToLatestVersion();
_handler?.Invoke(ev);
}
catch (Exception e)
{
EventParsingFailed?.Invoke(this, new EventParsingFailedArgs(resolvedEvent, e));
}
return(Task.CompletedTask);
}