NH-3919 - Allow reverting to DateTime.

Author: fredericDelaporte

src/NHibernate.Test/DialectTest/MsSql2008DialectFixture.cs

@@ -1,18 +1,20 @@
-using System.Reflection;
+using System;
+using System.Reflection;
 using NHibernate.Cfg;
 using NHibernate.Dialect;
 using NHibernate.Engine;
 using NHibernate.SqlTypes;
 using NHibernate.Type;
 using NUnit.Framework;
+using Environment = NHibernate.Cfg.Environment;
 
 namespace NHibernate.Test.DialectTest
 {
 	[TestFixture]
 	public class MsSql2008DialectFixture
 	{
 		[Test]
-		public void CheckSql2005DateTimeTypes()
+		public void CheckPreSql2008DateTimeTypes()
 		{
 			var cfg = TestConfigurationHelper.GetDefaultConfiguration();
 			cfg.SetProperty(Environment.Dialect, typeof(MsSql2005Dialect).FullName);
@@ -45,6 +47,24 @@ public void CheckSql2008DateTimeTypes()
 #pragma warning restore 618
 		}
 
+		[Test]
+		public void CheckKeepDateTime()
+		{
+			var cfg = TestConfigurationHelper.GetDefaultConfiguration();
+			cfg.SetProperty(Environment.Dialect, typeof(MsSql2008Dialect).FullName);
+			cfg.SetProperty(Environment.SqlTypesKeepDateTime, "true");
+			var mapping = GetMapping(cfg);
+			AssertSqlType(NHibernateUtil.DateTime, SqlTypeFactory.DateTime, mapping);
+			AssertSqlType(NHibernateUtil.Timestamp, SqlTypeFactory.DateTime, mapping);
+			AssertSqlType(NHibernateUtil.TimestampUtc, SqlTypeFactory.DateTime, mapping);
+			AssertSqlType(NHibernateUtil.DbTimestamp, SqlTypeFactory.DateTime, mapping);
+			AssertSqlType(NHibernateUtil.LocalDateTime, SqlTypeFactory.DateTime, mapping);
+			AssertSqlType(NHibernateUtil.UtcDateTime, SqlTypeFactory.DateTime, mapping);
+#pragma warning disable 618 // DateTime2 is obsolete
+			AssertSqlType(NHibernateUtil.DateTime2, SqlTypeFactory.DateTime2, mapping);
+#pragma warning restore 618
+		}
+
 		private static readonly FieldInfo _mappingField =
 			typeof(Configuration).GetField("mapping", BindingFlags.Instance | BindingFlags.NonPublic);
 

src/NHibernate/Cfg/Environment.cs

@@ -208,6 +208,12 @@ public static string Version
 		/// </summary>
 		public const string OdbcDateTimeScale = "odbc.explicit_datetime_scale";
 
+		/// <summary>
+		/// Disable switching built-in NHibernate date-time types from DbType.DateTime to DbType.DateTime2
+		/// for dialects supporting datetime2.
+		/// </summary>
+		public const string SqlTypesKeepDateTime = "sql_types.keep_datetime";
+
 		/// <summary>
 		/// <para>Oracle has a dual Unicode support model.</para>
 		/// <para>Either the whole database use an Unicode encoding, and then all string types

src/NHibernate/Dialect/MsSql2008Dialect.cs

@@ -1,16 +1,37 @@
 using System.Collections.Generic;
 using System.Data;
-using NHibernate.Cfg;
 using NHibernate.Dialect.Function;
 using NHibernate.Driver;
 using NHibernate.SqlTypes;
 using NHibernate.Type;
 using NHibernate.Util;
+using Environment = NHibernate.Cfg.Environment;
 
 namespace NHibernate.Dialect
 {
 	public class MsSql2008Dialect : MsSql2005Dialect
 	{
+		/// <summary>
+		/// Should <see cref="DbType.DateTime" /> be preserved instead of switching it to <see cref="DbType.DateTime2" />?
+		/// </summary>
+		/// <value>
+		/// <see langword="true" /> for preserving <see cref="DbType.DateTime" />, <see langword="false" /> for
+		/// replacing it with <see cref="DbType.DateTime2" />.
+		/// </value>
+		protected bool KeepDateTime { get; private set; }
+
+		public override void Configure(IDictionary<string, string> settings)
+		{
+			base.Configure(settings);
+
+			KeepDateTime = PropertiesHelper.GetBoolean(Environment.SqlTypesKeepDateTime, settings, false);
+			if (KeepDateTime)
+			{
+				// Re-register functions, they depend on this setting.
+				RegisterFunctions();
+			}
+		}
+
 		protected override void RegisterDateTimeTypeMappings()
 		{
 			base.RegisterDateTimeTypeMappings();
@@ -23,8 +44,15 @@ protected override void RegisterDateTimeTypeMappings()
 		protected override void RegisterFunctions()
 		{
 			base.RegisterFunctions();
-			RegisterFunction("current_timestamp", new NoArgSQLFunction("sysdatetime", NHibernateUtil.DateTime, true));
-			RegisterFunction("current_timestamp_offset", new NoArgSQLFunction("sysdatetimeoffset", NHibernateUtil.DateTimeOffset, true));
+			if (!KeepDateTime)
+			{
+				RegisterFunction(
+					"current_timestamp",
+					new NoArgSQLFunction("sysdatetime", NHibernateUtil.DateTime, true));
+			}
+			RegisterFunction(
+				"current_timestamp_offset",
+				new NoArgSQLFunction("sysdatetimeoffset", NHibernateUtil.DateTimeOffset, true));
 		}
 
 		protected override void RegisterKeywords()
@@ -42,21 +70,26 @@ protected override void RegisterDefaultProperties()
 		}
 
 		public override string CurrentTimestampSQLFunctionName =>
-			"SYSDATETIME()";
+			KeepDateTime ? base.CurrentTimestampSQLFunctionName : "SYSDATETIME()";
 
 		public override long TimestampResolutionInTicks =>
-			// MS SQL resolution with datetime2 is 100ns, one tick.
-			1;
+			KeepDateTime
+				? base.TimestampResolutionInTicks
+				// MS SQL resolution with datetime2 is 100ns, one tick.
+				: 1;
 
 		/// <inheritdoc />
 		public override SqlType[] RefineSqlTypes(IType type, SqlType[] types)
 		{
-			switch (type)
+			if (!KeepDateTime)
 			{
-				// Switch built-in DateTime types and their descendants to DateTime2.
-				case DateTimeType _:
-				case TimestampType _:
-					return new[] { SqlTypeFactory.DateTime2 };
+				switch (type)
+				{
+					// Switch built-in DateTime types and their descendants to DateTime2.
+					case DateTimeType _:
+					case TimestampType _:
+						return new[] { SqlTypeFactory.DateTime2 };
+				}
 			}
 			return base.RefineSqlTypes(type, types);
 		}

src/NHibernate/nhibernate-configuration.xsd

@@ -161,6 +161,14 @@
 										</xs:documentation>
 									</xs:annotation>
 								</xs:enumeration>
+								<xs:enumeration value="sql_types.keep_datetime">
+									<xs:annotation>
+										<xs:documentation>
+											Disable switching built-in NHibernate date-time types from DbType.DateTime to DbType.DateTime2
+											for dialects supporting datetime2.
+										</xs:documentation>
+									</xs:annotation>
+								</xs:enumeration>
 							</xs:restriction>
 						</xs:simpleType>
 					</xs:attribute>