small tweak to how mongo db fetches messages

src/MongoDb/CleanUp/Cleaner.cs

@@ -9,7 +9,7 @@ internal sealed class Cleaner<TMessage>(
     MongoDbCleanUpSettings settings,
     MongoDbCleanUpCollectionSettings<TMessage> collectionSettings,
     IMongoDatabase db,
-    TimeProvider timeProvider) : IOutboxCleaner where TMessage : IMessage
+    TimeProvider timeProvider) : IOutboxCleaner where TMessage : class, IMessage
 {
     private readonly IMongoCollection<TMessage> _collection = db.GetCollection<TMessage>(collectionSettings.Name);
 

src/MongoDb/CleanUp/MongoDbCleanUpSettings.cs

@@ -8,7 +8,7 @@ internal sealed record MongoDbCleanUpSettings
     public TimeSpan MaxAge { get; init; } = TimeSpan.FromDays(1);
 }
 
-internal sealed record MongoDbCleanUpCollectionSettings<TMessage> where TMessage : IMessage
+internal sealed record MongoDbCleanUpCollectionSettings<TMessage> where TMessage : class, IMessage
 {
     public required string Name { get; init; } 
     public required Expression<Func<TMessage, DateTime?>> ProcessedAtSelector { get; init; }

src/MongoDb/Polling/BatchCompleter.cs

@@ -5,7 +5,7 @@
 
 namespace YakShaveFx.OutboxKit.MongoDb.Polling;
 
-internal sealed class BatchCompleter<TMessage, TId> : IBatchCompleteRetrier where TMessage : IMessage
+internal sealed class BatchCompleter<TMessage, TId> : IBatchCompleteRetrier where TMessage : class, IMessage
 {
     private readonly IMongoCollection<TMessage> _collection;
     private readonly TimeProvider _timeProvider;

src/MongoDb/Polling/BatchFetcher.cs

@@ -6,7 +6,7 @@
 namespace YakShaveFx.OutboxKit.MongoDb.Polling;
 
 // ReSharper disable once ClassNeverInstantiated.Global - automagically instantiated by DI
-internal sealed class BatchFetcher<TMessage, TId> : IBatchFetcher where TMessage : IMessage
+internal sealed class BatchFetcher<TMessage, TId> : IBatchFetcher where TMessage : class, IMessage
 {
     private readonly IMongoCollection<TMessage> _collection;
     private readonly DistributedLockThingy _lockThingy;
@@ -77,14 +77,13 @@ public async Task<IBatchContext> FetchAndHoldAsync(CancellationToken ct)
 
     private async Task<IReadOnlyCollection<IMessage>> FetchMessagesAsync(CancellationToken ct)
     {
-        var messages = await _collection.Find(_findFilter).Sort(_sort).Limit(_batchSize).ToListAsync(ct);
-        var cast = new IMessage[messages.Count];
-        for (var i = 0; i < messages.Count; i++)
+        var messages = new List<TMessage>(_batchSize);
+        using var cursor = await _collection.Find(_findFilter).Sort(_sort).Limit(_batchSize).ToCursorAsync(ct);
+        while (await cursor.MoveNextAsync(ct))
         {
-            cast[i] = messages[i];
+            messages.AddRange(cursor.Current);
         }
-
-        return cast;
+        return messages;
     }
 
     private Task<bool> HasNextAsync(CancellationToken ct) => _collection.Find(_findFilter).Limit(1).AnyAsync(ct);

src/MongoDb/Polling/ConfigurationExtensions.cs

@@ -61,7 +61,7 @@ public interface IMongoDbPollingOutboxKitConfigurator
     /// <returns>The <see cref="IMongoDbPollingOutboxKitConfigurator"/> instance for chaining calls.</returns>
     IMongoDbPollingOutboxKitConfigurator WithCollection<TMessage, TId>(
         Action<IMongoDbOutboxCollectionConfigurator<TMessage, TId>> configure)
-        where TMessage : IMessage;
+        where TMessage : class, IMessage;
 
     /// <summary>
     /// Configures the outbox polling interval.
@@ -99,7 +99,7 @@ IMongoDbPollingOutboxKitConfigurator WithCollection<TMessage, TId>(
 /// </summary>
 /// <typeparam name="TMessage">The type of the message in the outbox.</typeparam>
 /// <typeparam name="TId">The type of the id of the message in the outbox.</typeparam>
-public interface IMongoDbOutboxCollectionConfigurator<TMessage, TId> where TMessage : IMessage
+public interface IMongoDbOutboxCollectionConfigurator<TMessage, TId> where TMessage : class, IMessage
 {
     /// <summary>
     /// Configures the name of the outbox collection.

src/MongoDb/Polling/ConfigurationImplementation.cs

@@ -13,7 +13,7 @@ namespace YakShaveFx.OutboxKit.MongoDb.Polling;
 internal interface IGetMongoDbOutboxCollectionConfigured
 {
     void ConfigureCollection<TMessage, TId>(MongoDbPollingCollectionSettings<TMessage, TId> collectionSettings)
-        where TMessage : IMessage;
+        where TMessage : class, IMessage;
 }
 
 internal interface IMongoDbOutboxCollectionConfigurator
@@ -24,7 +24,7 @@ internal interface IMongoDbOutboxCollectionConfigurator
 internal sealed class MongoDbOutboxCollectionConfigurator<TMessage, TId>(
     MongoDbPollingCollectionSettings<TMessage, TId>? defaults)
     : IMongoDbOutboxCollectionConfigurator, IMongoDbOutboxCollectionConfigurator<TMessage, TId>
-    where TMessage : IMessage
+    where TMessage : class, IMessage
 {
     private MongoDbPollingCollectionSettings<TMessage, TId> _settings = defaults ?? new();
 
@@ -89,7 +89,7 @@ public IMongoDbPollingOutboxKitConfigurator WithDatabaseFactory(
     }
 
     public IMongoDbPollingOutboxKitConfigurator WithCollection<TMessage, TId>(
-        Action<IMongoDbOutboxCollectionConfigurator<TMessage, TId>> configure) where TMessage : IMessage
+        Action<IMongoDbOutboxCollectionConfigurator<TMessage, TId>> configure) where TMessage : class, IMessage
     {
         ArgumentNullException.ThrowIfNull(configure);
         var configurator = new MongoDbOutboxCollectionConfigurator<TMessage, TId>(null);
@@ -189,7 +189,7 @@ private sealed class GetMongoDbOutboxCollectionConfigured(
     {
         public void ConfigureCollection<TMessage, TId>(
             MongoDbPollingCollectionSettings<TMessage, TId> collectionSettings)
-            where TMessage : IMessage
+            where TMessage : class, IMessage
         {
             if (string.IsNullOrWhiteSpace(collectionSettings.Name))
                 throw new InvalidOperationException("Collection name must be set");
@@ -321,7 +321,7 @@ internal sealed record MongoDbPollingSettings
     public CompletionMode CompletionMode { get; init; } = CompletionMode.Delete;
 }
 
-internal sealed record MongoDbPollingCollectionSettings<TMessage, TId> where TMessage : IMessage
+internal sealed record MongoDbPollingCollectionSettings<TMessage, TId> where TMessage : class, IMessage
 {
     public string Name { get; init; } = "outbox_messages";
     public Expression<Func<TMessage, TId>> IdSelector { get; init; } = null!;