Fixes #3421

Author: nfplee

src/NHibernate.Test/NHSpecificTest/GH3421/Entity.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+
+namespace NHibernate.Test.NHSpecificTest.GH3421
+{
+	class Entity
+	{
+		public virtual Guid Id { get; set; }
+		public virtual string Name { get; set; }
+
+		private IDictionary<string, object> _attributes;
+		public virtual IDictionary<string, object> Attributes {
+			get {
+				if (_attributes == null)
+					_attributes = new Dictionary<string, object>();
+				return _attributes;
+			}
+			set => _attributes = value;
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH3421/Fixture.cs

@@ -0,0 +1,97 @@
+using System.Collections.Generic;
+using System.Linq;
+using NHibernate.Cfg;
+using NHibernate.Cfg.MappingSchema;
+using NHibernate.Mapping.ByCode;
+using NHibernate.SqlCommand;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH3421
+{
+	[TestFixture]
+	public class ByCodeFixture : TestCaseMappingByCode
+	{
+		private SqlInterceptor _interceptor;
+
+		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);
+				rc.Component(x => x.Attributes, new {
+					Sku = (string)null
+				}, dc => {
+					dc.Property(x => x.Sku);
+				});
+			});
+
+			return mapper.CompileMappingForAllExplicitlyAddedEntities();
+		}
+
+		protected override void Configure(Configuration configuration)
+		{
+			base.Configure(configuration);
+
+			_interceptor = new SqlInterceptor();
+
+			configuration.SetInterceptor(_interceptor);
+		}
+
+		protected override void OnSetUp()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				var e1 = new Entity { Name = "Bob" };
+				session.Save(e1);
+
+				var e2 = new Entity { Name = "Sally", Attributes = new Dictionary<string, object>() {
+					{ "Sku", "AAA" }
+				} };
+				session.Save(e2);
+
+				transaction.Commit();
+			}
+		}
+
+		protected override void OnTearDown()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				session.CreateQuery("delete from Entity").ExecuteUpdate();
+				transaction.Commit();
+			}
+		}
+
+		[Test]
+		public void TestFlushDoesNotTriggerAnUpdate()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				var foo = session.Query<Entity>().ToList();
+
+				session.Flush();
+
+				var updateStatements = _interceptor.SqlStatements.Where(s => s.ToString().ToUpper().Contains("UPDATE")).ToList();
+
+				Assert.That(updateStatements, Has.Count.EqualTo(0));
+			}
+		}
+
+		public class SqlInterceptor : EmptyInterceptor
+		{
+			public IList<SqlString> SqlStatements = new List<SqlString>();
+
+			public override SqlString OnPrepareStatement(SqlString sql)
+			{
+				SqlStatements.Add(sql);
+
+				return base.OnPrepareStatement(sql);
+			}
+		}
+	}
+}

src/NHibernate/Type/ComponentType.cs

@@ -156,14 +156,6 @@ public override bool IsDirty(object x, object y, ISessionImplementor session)
 			{
 				return false;
 			}
-			/* 
-			 * NH Different behavior : we don't use the shortcut because NH-1101 
-			 * let the tuplizer choose how cosiderer properties when the component is null.
-			 */
-			if (EntityMode != EntityMode.Poco && (x == null || y == null))
-			{
-				return true;
-			}
 			object[] xvalues = GetPropertyValues(x);
 			object[] yvalues = GetPropertyValues(y);
 			for (int i = 0; i < xvalues.Length; i++)
@@ -182,14 +174,6 @@ public override bool IsDirty(object x, object y, bool[] checkable, ISessionImple
 			{
 				return false;
 			}
-			/* 
-			 * NH Different behavior : we don't use the shortcut because NH-1101 
-			 * let the tuplizer choose how cosiderer properties when the component is null.
-			 */
-			if (EntityMode != EntityMode.Poco && (x == null || y == null))
-			{
-				return true;
-			}
 			object[] xvalues = GetPropertyValues(x);
 			object[] yvalues = GetPropertyValues(y);
 			int loc = 0;