Fix for np() opererator for Nullable (e.g. DateTime) (#270)

* Fixed np() operator for DateTime / DateTime?

* 14

Author: StefH

Directory.Build.props

@@ -4,7 +4,7 @@
   </PropertyGroup>
 
   <PropertyGroup>
-    <VersionPrefix>1.0.13</VersionPrefix>
+    <VersionPrefix>1.0.14</VersionPrefix>
   </PropertyGroup>
 
   <Choose>

GitHubReleaseNotes.txt

@@ -1,3 +1,3 @@
 https://github.com/StefH/GitHubReleaseNotes
 
-GitHubReleaseNotes.exe . --output CHANGELOG.md --skip-empty-releases --language en --version 1.0.13.0
+GitHubReleaseNotes.exe . --output CHANGELOG.md --skip-empty-releases --language en --version 1.0.14.0

src/System.Linq.Dynamic.Core/Parser/ExpressionParser.cs

@@ -1177,7 +1177,7 @@ Expression GenerateConditional(Expression test, Expression expr1, Expression exp
                     // - convert expr2 to nullable
                     if (Constants.IsNull(expr1) && expr2.Type.GetTypeInfo().IsValueType)
                     {
-                        Type nullableType = typeof(Nullable<>).MakeGenericType(expr2.Type);
+                        Type nullableType = TypeHelper.ToNullableType(expr2.Type);
                         expr1 = Expression.Constant(null, nullableType);
                         expr2 = Expression.Convert(expr2, nullableType);
                     }
@@ -1187,7 +1187,7 @@ Expression GenerateConditional(Expression test, Expression expr1, Expression exp
                     // - convert expr1 to nullable
                     if (Constants.IsNull(expr2) && expr1.Type.GetTypeInfo().IsValueType)
                     {
-                        Type nullableType = typeof(Nullable<>).MakeGenericType(expr1.Type);
+                        Type nullableType = TypeHelper.ToNullableType(expr1.Type);
                         expr2 = Expression.Constant(null, nullableType);
                         expr1 = Expression.Convert(expr1, nullableType);
                     }

src/System.Linq.Dynamic.Core/Parser/TypeHelper.cs

@@ -260,6 +260,13 @@ public static bool IsNullableType(Type type)
             return type.GetTypeInfo().IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>);
         }
 
+        public static Type ToNullableType(Type type)
+        {
+            Check.NotNull(type, nameof(type));
+
+            return IsNullableType(type) ? type : typeof(Nullable<>).MakeGenericType(type);
+        }
+
         public static bool IsSignedIntegralType(Type type)
         {
             return GetNumericTypeKind(type) == 2;

test/System.Linq.Dynamic.Core.Tests/ExpressionTests.cs

@@ -1290,7 +1290,39 @@ public void ExpressionTests_NullCoalescing()
         }
 
         [Fact]
-        public void ExpressionTests_NullPropagating_Null()
+        public void ExpressionTests_NullPropagating_DateTime_Value()
+        {
+            // Arrange
+            var q = new[] {
+                new { id = 1, date1 = (DateTime?) DateTime.Now, date2 = DateTime.Now.AddDays(-1)}
+            }.AsQueryable();
+
+            // Act
+            var result = q.OrderBy(x => x.date2).Select(x => x.id).ToArray();
+            var resultDynamic = q.OrderBy("np(date2)").Select("id").ToDynamicArray<int>();
+
+            // Assert
+            Check.That(resultDynamic).ContainsExactly(result);
+        }
+
+        [Fact]
+        public void ExpressionTests_NullPropagating_NullableDateTime()
+        {
+            // Arrange
+            var q = new[] {
+                new { id = 1, date1 = (DateTime?) DateTime.Now, date2 = DateTime.Now.AddDays(-1)}
+            }.AsQueryable();
+
+            // Act
+            var result = q.OrderBy(x => x.date1).Select(x => x.id).ToArray();
+            var resultDynamic = q.OrderBy("np(date1)").Select("id").ToDynamicArray<int>();
+
+            // Assert
+            Check.That(resultDynamic).ContainsExactly(result);
+        }
+
+        [Fact]
+        public void ExpressionTests_NullPropagating_Integer_Null()
         {
             // Arrange
             var testModels = User.GenerateSampleModels(2, true).ToList();
@@ -1306,7 +1338,7 @@ public void ExpressionTests_NullPropagating_Null()
         }
 
         [Fact]
-        public void ExpressionTests_NullPropagating_Value()
+        public void ExpressionTests_NullPropagating_Integer_Value()
         {
             // Arrange
             var testModels = User.GenerateSampleModels(2, true).ToList();