Read stream from EventStore without "stream doesn't exist exception"

Question

Application written in .net tries to read event stream. For this goal, EventStoreCleint wrapper was written, under the hood it uses EventStore.Client.Grpc.Streams 23.1.0. The logic is the following:

• try to read stream
• if there is no stream (or stream version is 0) we can continue and send TenantCreated event
• if there is a stream (or stream version is > 0) application will not apply TenantCreated event.

The problem is in fact, when the application reads the event stream by _client.ReadStreamAsync if there is no stream, the exception will be thrown. Exceptions are expensive from the performance point of view.

How to read stream even is stream version is 0 without exceptions?

Answer 1

If you inspect the StreamState in the result, it will be StreamNotFound

var res = await conn.ReadStreamAsync(Direction.Forwards, streamName, startPosition, Int64.MaxValue, resolveLinkTos: false, cancellationToken: ct)
if (res.ReadState == ReadState.StreamNotFound)
   // TODO handle empty

Example in Equinox

When writing, ConditionalAppendToStreamAsync don't throw an exception either; you inspect the Status of the result.

Example in Equinox

Answer 2

Key thing is to not enumerate events immediately e.g.:

_client.ReadStreamAsync(Direction.Forwards, name, StreamPosition.Start).ToListAsync().Result

Instead use something like this:

var res = await _client.ReadStreamAsync(Direction.Forwards, name, StreamPosition.Start);
if (res.ReadState == ReadState.Ok)
    events = res.ToListAsync();