Added comments with en explanation for the EventStoreDBSubscriptionCheckpointRepository

Author: oskardudycz

Core.EventStoreDB/Events/AggregateStreamExtensions.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Threading;
 using System.Threading.Tasks;
-using Core.Aggregates;
 using Core.Events;
 using Core.EventStoreDB.Serialization;
 using Core.Projections;

Core.EventStoreDB/Subscriptions/EventStoreDBSubscriptionCheckpointRepository.cs

@@ -46,6 +46,7 @@ public async ValueTask Store(string subscriptionId, ulong position, Cancellation
 
             try
             {
+                // store new checkpoint expecting stream to exist
                 await eventStoreClient.AppendToStreamAsync(
                     streamName,
                     StreamState.StreamExists,
@@ -55,13 +56,17 @@ await eventStoreClient.AppendToStreamAsync(
             }
             catch (WrongExpectedVersionException)
             {
+                // WrongExpectedVersionException means that stream did not exist
+                // Set the checkpoint stream to have at most 1 event
+                // using stream metadata $maxCount property
                 await eventStoreClient.SetStreamMetadataAsync(
                     streamName,
                     StreamState.NoStream,
                     new StreamMetadata(1),
                     cancellationToken: ct
                 );
 
+                // append event again expecting stream to not exist
                 await eventStoreClient.AppendToStreamAsync(
                     streamName,
                     StreamState.NoStream,