Fix np(...) with UnaryExpression (#509)

Author: StefH

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

@@ -294,7 +294,11 @@ public bool TryGenerateAndAlsoNotNullExpression(Expression sourceExpression, boo
 
         public bool ExpressionQualifiesForNullPropagation(Expression expression)
         {
-            return expression is MemberExpression || expression is ParameterExpression || expression is MethodCallExpression;
+            return
+                expression is MemberExpression ||
+                expression is ParameterExpression || 
+                expression is MethodCallExpression ||
+                expression is UnaryExpression;
         }
 
         private Expression GetMemberExpression(Expression expression)
@@ -349,6 +353,11 @@ private List<Expression> CollectExpressions(bool addSelf, Expression sourceExpre
                         expressionRecognized = expression != null;
                         break;
 
+                    case UnaryExpression unaryExpression:
+                        expression = GetUnaryExpression(unaryExpression);
+                        expressionRecognized = expression != null;
+                        break;
+
                     default:
                         expressionRecognized = false;
                         break;
@@ -374,5 +383,10 @@ private static Expression GetMethodCallExpression(MethodCallExpression methodCal
             // Something like: "np(MyClasses.FirstOrDefault())"
             return methodCallExpression.Arguments.FirstOrDefault();
         }
+
+        private static Expression GetUnaryExpression(UnaryExpression unaryExpression)
+        {
+            return unaryExpression.Operand;
+        }
     }
 }

test/System.Linq.Dynamic.Core.Tests/QueryableTests.Is,OfType,As,Cast.cs

@@ -1,6 +1,8 @@
-using NFluent;
+using System.Collections.Generic;
 using System.Linq.Dynamic.Core.Exceptions;
 using System.Linq.Dynamic.Core.Tests.Entities;
+using FluentAssertions;
+using NFluent;
 using Xunit;
 
 namespace System.Linq.Dynamic.Core.Tests
@@ -175,6 +177,32 @@ public void As_Dynamic_ActingOnIt_WithType()
             Check.That(countAsDynamic).Equals(1);
         }
 
+        public class AS_A { }
+        public class AS_B : AS_A
+        {
+            public string MyProperty { get; set; }
+        }
+
+        [Fact]
+        [Trait("bug", "452")]
+        public void As_UnaryExpression()
+        {
+            // Arrange
+            var a = new AS_A();
+            var b = new AS_B { MyProperty = "x" };
+            var lst = new List<AS_A>()
+            {
+                a,
+                b
+            };
+
+            // Act
+            var result = lst.AsQueryable().Where($"np(as(\"{typeof(AS_B).FullName}\").MyProperty) = \"x\"");
+
+            // Assert
+            result.ToDynamicArray().Should().HaveCount(1).And.Contain(b);
+        }
+
         [Fact]
         public void CastToType_WithType()
         {