fixes dotnet#26742

Author: EamonHetherton

src/EFCore.SqlServer/Storage/Internal/SqlServerDateTimeTypeMapping.cs

@@ -25,7 +25,7 @@ public class SqlServerDateTimeTypeMapping : DateTimeTypeMapping
         // so the order of the entries in this array is important
         private readonly string[] _dateTime2Formats =
         {
-            "'{0:yyyy-MM-ddTHH:mm:ss}'",
+            "'{0:yyyy-MM-ddTHH:mm:ssK}'",
             "'{0:yyyy-MM-ddTHH:mm:ss.fK}'",
             "'{0:yyyy-MM-ddTHH:mm:ss.ffK}'",
             "'{0:yyyy-MM-ddTHH:mm:ss.fffK}'",
@@ -89,10 +89,21 @@ protected override void ConfigureParameter(DbParameter parameter)
 
             if (Precision.HasValue)
             {
-                parameter.Precision = unchecked((byte)Precision.Value);
+                // Workaround for inconsistant definition of precision/scale between EF and SQLClient for VarTime types
+                if (IsVarTime(((SqlParameter)parameter).SqlDbType))
+                {
+                    parameter.Scale = unchecked((byte)Precision.Value);
+                }
+                else
+                {
+                    parameter.Precision = unchecked((byte)Precision.Value);
+                }
             }
         }
 
+        private static bool IsVarTime(SqlDbType type) =>
+            type == SqlDbType.Time || type == SqlDbType.DateTime2 || type == SqlDbType.DateTimeOffset;
+
         /// <summary>
         ///     Creates a copy of this mapping.
         /// </summary>

test/EFCore.SqlServer.FunctionalTests/Query/QueryBugsTest.cs

@@ -7041,7 +7041,7 @@ public enum BusinessType18346
         public virtual async Task Thread_safety_in_relational_command_cache()
         {
             var contextFactory = await InitializeAsync<MyContext21666>(
-                onConfiguring: options =>((IDbContextOptionsBuilderInfrastructure)options).AddOrUpdateExtension(
+                onConfiguring: options => ((IDbContextOptionsBuilderInfrastructure)options).AddOrUpdateExtension(
                     options.Options.FindExtension<SqlServerOptionsExtension>()
                         .WithConnection(null)
                         .WithConnectionString(SqlServerTestStore.CreateConnectionString(StoreName))));
@@ -10345,6 +10345,59 @@ public class CollectionViewModel25225
 
         #endregion
 
+        #region Issue26742
+        [ConditionalTheory]
+        [InlineData(null, "")]
+        //[InlineData(0, " (Scale = 0)")] //https://github.com/dotnet/SqlClient/issues/1380 prevents this passing, not EF
+        [InlineData(1, " (Scale = 1)")]
+        [InlineData(2, " (Scale = 2)")]
+        [InlineData(3, " (Scale = 3)")]
+        [InlineData(4, " (Scale = 4)")]
+        [InlineData(5, " (Scale = 5)")]
+        [InlineData(6, " (Scale = 6)")]
+        [InlineData(7, " (Scale = 7)")]
+        public virtual async Task Query_generates_correct_datetime2_parameter_definition(int? fractionalSeconds, string postfix)
+        {
+            var contextFactory = await InitializeAsync<MyContext_26742>(onModelCreating: modelBuilder =>
+            {
+                if (fractionalSeconds.HasValue)
+                {
+                    modelBuilder.Entity<MyContext_26742.Entity>().Property(p => p.DateTime).HasPrecision(fractionalSeconds.Value);
+                }
+            });
+
+            var parameter = new DateTime(2021, 11, 12, 13, 14, 15).AddTicks(1234567);
+
+            using (var context = contextFactory.CreateContext())
+            {
+                _ = context.Entities.FirstOrDefault(x => x.DateTime == parameter);
+
+                AssertSql(
+                    $@"@__parameter_0='2021-11-12T13:14:15.1234567'{postfix}
+
+SELECT TOP(1) [e].[Id], [e].[DateTime]
+FROM [Entities] AS [e]
+WHERE [e].[DateTime] = @__parameter_0");
+            }
+        }
+
+        protected class MyContext_26742 : DbContext
+        {
+            public DbSet<Entity> Entities { get; set; }
+
+            public MyContext_26742(DbContextOptions options)
+                : base(options)
+            {
+            }
+
+            public class Entity
+            {
+                public int Id { get; set; }
+                public DateTime DateTime { get; set; }
+            }
+        }
+        #endregion
+
         protected override string StoreName => "QueryBugsTest";
         protected TestSqlLoggerFactory TestSqlLoggerFactory
             => (TestSqlLoggerFactory)ListLoggerFactory;