Keep unbuffered async multi-map resources alive

Dapper/SqlMapper.Async.cs

@@ -934,17 +934,26 @@ private static async Task<IEnumerable<TReturn>> MultiMapAsync<TFirst, TSecond, T
             var identity = new Identity<TFirst, TSecond, TThird, TFourth, TFifth, TSixth, TSeventh>(command.CommandText, command.CommandTypeDirect, cnn, typeof(TFirst), param?.GetType());
             var info = GetCacheInfo(identity, param, command.AddToCache);
             bool wasClosed = cnn.State == ConnectionState.Closed;
+            DbCommand? cmd = null;
+            DbDataReader? reader = null;
             try
             {
                 if (wasClosed) await cnn.TryOpenAsync(command.CancellationToken).ConfigureAwait(false);
-                using var cmd = command.TrySetupAsyncCommand(cnn, info.ParamReader);
-                using var reader = await ExecuteReaderWithFlagsFallbackAsync(cmd, wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult, command.CancellationToken).ConfigureAwait(false);
-                if (!command.Buffered) wasClosed = false; // handing back open reader; rely on command-behavior
+                cmd = command.TrySetupAsyncCommand(cnn, info.ParamReader);
+                reader = await ExecuteReaderWithFlagsFallbackAsync(cmd, wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult, command.CancellationToken).ConfigureAwait(false);
                 var results = MultiMapImpl<TFirst, TSecond, TThird, TFourth, TFifth, TSixth, TSeventh, TReturn>(null, CommandDefinition.ForCallback(command.Parameters, command.Flags), map, splitOn, reader, identity, true);
-                return command.Buffered ? results.ToList() : results;
+                if (command.Buffered) return results.ToList();
+
+                var deferred = ExecuteReaderSync(results, reader, cmd, cnn, wasClosed);
+                reader = null;
+                cmd = null;
+                wasClosed = false;
+                return deferred;
             }
             finally
             {
+                reader?.Dispose();
+                cmd?.Dispose();
                 if (wasClosed) cnn.Close();
             }
         }
@@ -983,20 +992,44 @@ private static async Task<IEnumerable<TReturn>> MultiMapAsync<TReturn>(this IDbC
             var identity = new IdentityWithTypes(command.CommandText, command.CommandTypeDirect, cnn, types[0], param?.GetType(), types);
             var info = GetCacheInfo(identity, param, command.AddToCache);
             bool wasClosed = cnn.State == ConnectionState.Closed;
+            DbCommand? cmd = null;
+            DbDataReader? reader = null;
             try
             {
                 if (wasClosed) await cnn.TryOpenAsync(command.CancellationToken).ConfigureAwait(false);
-                using var cmd = command.TrySetupAsyncCommand(cnn, info.ParamReader);
-                using var reader = await ExecuteReaderWithFlagsFallbackAsync(cmd, wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult, command.CancellationToken).ConfigureAwait(false);
+                cmd = command.TrySetupAsyncCommand(cnn, info.ParamReader);
+                reader = await ExecuteReaderWithFlagsFallbackAsync(cmd, wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult, command.CancellationToken).ConfigureAwait(false);
                 var results = MultiMapImpl(null, default, types, map, splitOn, reader, identity, true);
-                return command.Buffered ? results.ToList() : results;
-            }
-            finally
-            {
-                if (wasClosed) cnn.Close();
+                if (command.Buffered) return results.ToList();
+
+                var deferred = ExecuteReaderSync(results, reader, cmd, cnn, wasClosed);
+                reader = null;
+                cmd = null;
+                wasClosed = false;
+                return deferred;
+            }
+            finally
+            {
+                reader?.Dispose();
+                cmd?.Dispose();
+                if (wasClosed) cnn.Close();
             }
         }
 
+        private static IEnumerable<T> ExecuteReaderSync<T>(IEnumerable<T> results, DbDataReader reader, DbCommand command, IDbConnection cnn, bool wasClosed)
+        {
+            try
+            {
+                foreach (var result in results) yield return result;
+            }
+            finally
+            {
+                reader.Dispose();
+                command.Dispose();
+                if (wasClosed) cnn.Close();
+            }
+        }
+
         private static IEnumerable<T> ExecuteReaderSync<T>(DbDataReader reader, Func<DbDataReader, object> func, object? parameters)
         {
             using (reader)

Directory.Packages.props

@@ -38,6 +38,7 @@
     <PackageVersion Include="RepoDb.SqlServer" Version="1.13.1" />
     <PackageVersion Include="ServiceStack.OrmLite.SqlServer" Version="10.0.6" />
     <PackageVersion Include="Snowflake.Data" Version="5.5.0" />
+    <PackageVersion Include="pengdows.crud.fakeDb" Version="2.0.5" />
     <PackageVersion Include="SqlMarshal" Version="0.5.0" />
     <PackageVersion Include="SubSonic" Version="3.0.0.4" />
     <PackageVersion Include="Susanoo.SqlServer" Version="1.2.4.2" />

tests/Dapper.Tests/Dapper.Tests.csproj

@@ -32,6 +32,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' != 'net481'">
+    <PackageReference Include="pengdows.crud.fakeDb" />
     <PackageReference Include="Npgsql" />
     <PackageReference Include="Snowflake.Data" />
   </ItemGroup>

tests/Dapper.Tests/FakeDbTests.Issue2099.cs

@@ -0,0 +1,32 @@
+#if !NET481
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Dapper;
+using pengdows.crud.fakeDb;
+using Xunit;
+
+namespace Dapper.Tests;
+
+public sealed class FakeDbIssue2099Tests
+{
+    [Fact]
+    public async Task UnbufferedAsyncMultiMapKeepsReaderAliveUntilEnumeration()
+    {
+        using var connection = new fakeDbConnection(new FakeDataStore());
+        connection.EnqueueReaderResult(new[]
+        {
+            new Dictionary<string, object?> { ["A"] = 1, ["B"] = 2 },
+        });
+        connection.Open();
+
+        var command = new CommandDefinition("select 1 as A, 2 as B", flags: CommandFlags.None);
+        var results = await connection.QueryAsync<First, Second, int>(command, (a, b) => a.A + b.B, splitOn: "B");
+
+        Assert.Equal(3, results.Single());
+    }
+
+    private sealed class First { public int A { get; set; } }
+    private sealed class Second { public int B { get; set; } }
+}
+#endif