Fix #3725: DbBatchBatcher empty batch execution bug

Add empty batch validation to DoExecuteBatch() and DoExecuteBatchAsync()
to prevent InvalidOperationException when ExecuteBatch is called with no
commands. This matches the pattern used in GenericBatchingBatcher.

Author: ja-kar

src/NHibernate.Test/Async/NHSpecificTest/GH3725/Fixture.cs

@@ -0,0 +1,82 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by AsyncGenerator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+
+using System.Linq;
+using NUnit.Framework;
+using NHibernate.Linq;
+
+namespace NHibernate.Test.NHSpecificTest.GH3725
+{
+	using System.Threading.Tasks;
+	[TestFixture]
+	public class FixtureAsync : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			var e1 = new Entity { Name = "Test" };
+			session.Save(e1);
+
+			transaction.Commit();
+		}
+
+		protected override void OnTearDown()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			session.CreateQuery("delete from System.Object").ExecuteUpdate();
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public async Task EmptyBatchShouldNotThrowExceptionAsync()
+		{
+			// This test verifies that DbBatchBatcher handles empty batches correctly
+			// The bug occurred when ExecuteBatch was called on an empty batch,
+			// causing InvalidOperationException: CommandText property has not been initialized
+
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			// Load an entity - this prepares a SELECT command
+			var entity = await (session.Query<Entity>().FirstOrDefaultAsync());
+			Assert.That(entity, Is.Not.Null);
+
+			// Now prepare a batch command which triggers ExecuteBatch on any existing batch
+			// If the previous command didn't add anything to the batch, this would fail
+			// before the fix with InvalidOperationException
+			var entity2 = await (session.Query<Entity>().FirstOrDefaultAsync());
+			Assert.That(entity2, Is.Not.Null);
+
+			await (transaction.CommitAsync());
+		}
+
+		[Test]
+		public async Task FlushEmptyBatchShouldNotThrowExceptionAsync()
+		{
+			// Another scenario where empty batch execution can occur
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			// Query without any modifications
+			var count = await (session.Query<Entity>().CountAsync());
+			Assert.That(count, Is.EqualTo(1));
+
+			// Flush with no pending batch operations should not throw
+			Assert.DoesNotThrowAsync(() => session.FlushAsync());
+
+			await (transaction.CommitAsync());
+		}
+	}
+}

src/NHibernate.Test/Async/NHSpecificTest/GH3725/FixtureByCode.cs

@@ -0,0 +1,92 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by AsyncGenerator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+
+using System.Linq;
+using NHibernate.Cfg.MappingSchema;
+using NHibernate.Mapping.ByCode;
+using NUnit.Framework;
+using NHibernate.Linq;
+
+namespace NHibernate.Test.NHSpecificTest.GH3725
+{
+	using System.Threading.Tasks;
+	/// <summary>
+	/// Fixture using 'by code' mappings
+	/// </summary>
+	/// <remarks>
+	/// This fixture is identical to <see cref="FixtureAsync" /> except the <see cref="Entity" /> mapping is performed
+	/// by code in the GetMappings method, and does not require the <c>Mappings.hbm.xml</c> file.
+	/// </remarks>
+	[TestFixture]
+	public class FixtureByCodeAsync : TestCaseMappingByCode
+	{
+		protected override HbmMapping GetMappings()
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<Entity>(rc =>
+			{
+				rc.Id(x => x.Id, m => m.Generator(Generators.GuidComb));
+				rc.Property(x => x.Name);
+			});
+
+			return mapper.CompileMappingForAllExplicitlyAddedEntities();
+		}
+
+		protected override void OnSetUp()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			var e1 = new Entity { Name = "Test" };
+			session.Save(e1);
+
+			transaction.Commit();
+		}
+
+		protected override void OnTearDown()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			session.CreateQuery("delete from System.Object").ExecuteUpdate();
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public async Task EmptyBatchShouldNotThrowExceptionAsync()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			var entity = await (session.Query<Entity>().FirstOrDefaultAsync());
+			Assert.That(entity, Is.Not.Null);
+
+			var entity2 = await (session.Query<Entity>().FirstOrDefaultAsync());
+			Assert.That(entity2, Is.Not.Null);
+
+			await (transaction.CommitAsync());
+		}
+
+		[Test]
+		public async Task FlushEmptyBatchShouldNotThrowExceptionAsync()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			var count = await (session.Query<Entity>().CountAsync());
+			Assert.That(count, Is.EqualTo(1));
+
+			Assert.DoesNotThrowAsync(() => session.FlushAsync());
+
+			await (transaction.CommitAsync());
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH3725/Entity.cs

@@ -0,0 +1,10 @@
+using System;
+
+namespace NHibernate.Test.NHSpecificTest.GH3725
+{
+	class Entity
+	{
+		public virtual Guid Id { get; set; }
+		public virtual string Name { get; set; }
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH3725/Fixture.cs

@@ -0,0 +1,70 @@
+using System.Linq;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH3725
+{
+	[TestFixture]
+	public class Fixture : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			var e1 = new Entity { Name = "Test" };
+			session.Save(e1);
+
+			transaction.Commit();
+		}
+
+		protected override void OnTearDown()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			session.CreateQuery("delete from System.Object").ExecuteUpdate();
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public void EmptyBatchShouldNotThrowException()
+		{
+			// This test verifies that DbBatchBatcher handles empty batches correctly
+			// The bug occurred when ExecuteBatch was called on an empty batch,
+			// causing InvalidOperationException: CommandText property has not been initialized
+
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			// Load an entity - this prepares a SELECT command
+			var entity = session.Query<Entity>().FirstOrDefault();
+			Assert.That(entity, Is.Not.Null);
+
+			// Now prepare a batch command which triggers ExecuteBatch on any existing batch
+			// If the previous command didn't add anything to the batch, this would fail
+			// before the fix with InvalidOperationException
+			var entity2 = session.Query<Entity>().FirstOrDefault();
+			Assert.That(entity2, Is.Not.Null);
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public void FlushEmptyBatchShouldNotThrowException()
+		{
+			// Another scenario where empty batch execution can occur
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			// Query without any modifications
+			var count = session.Query<Entity>().Count();
+			Assert.That(count, Is.EqualTo(1));
+
+			// Flush with no pending batch operations should not throw
+			Assert.DoesNotThrow(() => session.Flush());
+
+			transaction.Commit();
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH3725/FixtureByCode.cs

@@ -0,0 +1,80 @@
+using System.Linq;
+using NHibernate.Cfg.MappingSchema;
+using NHibernate.Mapping.ByCode;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH3725
+{
+	/// <summary>
+	/// Fixture using 'by code' mappings
+	/// </summary>
+	/// <remarks>
+	/// This fixture is identical to <see cref="Fixture" /> except the <see cref="Entity" /> mapping is performed
+	/// by code in the GetMappings method, and does not require the <c>Mappings.hbm.xml</c> file.
+	/// </remarks>
+	[TestFixture]
+	public class FixtureByCode : TestCaseMappingByCode
+	{
+		protected override HbmMapping GetMappings()
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<Entity>(rc =>
+			{
+				rc.Id(x => x.Id, m => m.Generator(Generators.GuidComb));
+				rc.Property(x => x.Name);
+			});
+
+			return mapper.CompileMappingForAllExplicitlyAddedEntities();
+		}
+
+		protected override void OnSetUp()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			var e1 = new Entity { Name = "Test" };
+			session.Save(e1);
+
+			transaction.Commit();
+		}
+
+		protected override void OnTearDown()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			session.CreateQuery("delete from System.Object").ExecuteUpdate();
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public void EmptyBatchShouldNotThrowException()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			var entity = session.Query<Entity>().FirstOrDefault();
+			Assert.That(entity, Is.Not.Null);
+
+			var entity2 = session.Query<Entity>().FirstOrDefault();
+			Assert.That(entity2, Is.Not.Null);
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public void FlushEmptyBatchShouldNotThrowException()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+
+			var count = session.Query<Entity>().Count();
+			Assert.That(count, Is.EqualTo(1));
+
+			Assert.DoesNotThrow(() => session.Flush());
+
+			transaction.Commit();
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH3725/Mappings.hbm.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHibernate.Test"
+                   namespace="NHibernate.Test.NHSpecificTest.GH3725">
+
+  <class name="Entity">
+    <id name="Id" generator="guid.comb"/>
+    <property name="Name"/>
+  </class>
+
+</hibernate-mapping>

src/NHibernate/AdoNet/DbBatchBatcher.cs

@@ -115,6 +115,12 @@ public override Task AddToBatchAsync(IExpectation expectation, CancellationToken
 
 		protected override void DoExecuteBatch(DbCommand ps)
 		{
+			if (_currentBatch.BatchCommands.Count == 0)
+			{
+				Expectations.VerifyOutcomeBatched(_totalExpectedRowsAffected, 0, ps);
+				return;
+			}
+
 			try
 			{
 				Log.Debug("Executing batch");
@@ -145,6 +151,12 @@ protected override void DoExecuteBatch(DbCommand ps)
 		protected override async Task DoExecuteBatchAsync(DbCommand ps, CancellationToken cancellationToken)
 		{
 			cancellationToken.ThrowIfCancellationRequested();
+			if (_currentBatch.BatchCommands.Count == 0)
+			{
+				Expectations.VerifyOutcomeBatched(_totalExpectedRowsAffected, 0, ps);
+				return;
+			}
+
 			try
 			{
 				Log.Debug("Executing batch");