Issue215

src/System.Linq.Dynamic.Core/DynamicClassFactory.cs

@@ -264,7 +264,10 @@ public static Type CreateType([NotNull] IList<DynamicProperty> properties, bool
                             ilgeneratorToString.Emit(OpCodes.Pop);
                         }
 
-                        if (createParameterCtor)
+                        // Only create the default and with params constructor when there are any params.
+                        // Otherwise default constructor is not needed because it matches the default
+                        // one provided by the runtime when no constructor is present
+                        if (createParameterCtor && names.Any())
                         {
                             // .ctor default
                             ConstructorBuilder constructorDef = tb.DefineConstructor(MethodAttributes.Public | MethodAttributes.HideBySig, CallingConventions.HasThis, EmptyTypes);

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

@@ -1531,11 +1531,13 @@ Expression ParseMemberAccess(Type type, Expression instance)
                 return Expression.Dynamic(new DynamicGetMemberBinder(id), type, instance);
             }
 #endif
-
-            MethodInfo indexerMethod = instance.Type.GetMethod("get_Item", new[] { typeof(string) });
-            if (indexerMethod != null)
+            if (!_parsingConfig.DisableMemberAccessToIndexAccesorDowncast)
             {
-                return Expression.Call(instance, indexerMethod, Expression.Constant(id));
+                MethodInfo indexerMethod = instance.Type.GetMethod("get_Item", new[] {typeof(string)});
+                if (indexerMethod != null)
+                {
+                    return Expression.Call(instance, indexerMethod, Expression.Constant(id));
+                }
             }
 
             if (_textParser.CurrentToken.Id == TokenId.Lambda && _it.Type == type)

src/System.Linq.Dynamic.Core/ParsingConfig.cs

@@ -103,5 +103,12 @@ public IExpressionPromoter ExpressionPromoter
         /// Renames the (Typed)ParameterExpression empty Name to a the correct supplied name from `it`. Default value is false.
         /// </summary>
         public bool RenameParameterExpression { get; set; } = false;
+
+        /// <summary>
+        /// By default when a member is not found in a type and the type has a string bassed index accessor it will be parsed as an index accesor. Use
+        /// this flag to disable this behaviour and have parsing fail when parsing an expression
+        /// where a member access on a non existing member happens
+        /// </summary>
+        public bool DisableMemberAccessToIndexAccesorDowncast { get; set; } = false;
     }
 }

test/System.Linq.Dynamic.Core.Tests/EntitiesTests.Select.cs

@@ -1,5 +1,7 @@
 using System.Collections;
+using System.Linq.Dynamic.Core.Exceptions;
 using System.Linq.Dynamic.Core.Tests.Helpers.Entities;
+using MongoDB.Bson;
 #if EFCORE
 using Microsoft.EntityFrameworkCore;
 #else
@@ -48,6 +50,42 @@ public void Entities_Select_SingleColumn()
             Assert.Equal<ICollection>(expected, test);
         }
 
+        [Fact]
+        public void Entities_Select_EmptyObject()
+        {
+            ParsingConfig config = ParsingConfig.Default;
+            config.EvaluateGroupByAtDatabase = true;
+
+            //Arrange
+            PopulateTestData(5, 0);
+
+            var expected = _context.Blogs.Select(x => new {}).ToList();
+
+            //Act
+            var test = _context.Blogs.GroupBy(config, "BlogId", "new()").Select<object>("new()").ToList();
+
+            //Assert
+            Assert.Equal(expected.ToJson(), test.ToJson());
+        }
+
+        [Fact]
+        public void Entities_Select_BrokenObject()
+        {
+            ParsingConfig config = ParsingConfig.Default;
+            config.DisableMemberAccessToIndexAccesorDowncast = false;
+
+            // Silently creates something that will later fail on materialization
+            var test = _context.Blogs.Select(config, "new(~.BlogId)");
+            test = test.Select(config, "new(nonexistentproperty as howcanthiswork)");
+
+            // Will fail when creating the expression
+            config.DisableMemberAccessToIndexAccesorDowncast = true;
+            Assert.ThrowsAny<ParseException>(() =>
+            {
+                test = test.Select(config, "new(nonexistentproperty as howcanthiswork)");
+            });
+        }
+
         [Fact]
         public void Entities_Select_MultipleColumn()
         {
@@ -108,4 +146,4 @@ public void Entities_Select_BlogAndPosts()
             }
         }
     }
-}
+}