Better handling of MemberName extraction for broken circumstances (im…

…provement of previous commit).

src/ExpressiveAnnotations.Tests/AttribsTest.cs

@@ -321,6 +321,45 @@ public void throw_when_requirement_is_applied_to_field_of_non_nullable_value_typ
                 e.InnerException.Message);
         }
 
+        [Fact]
+        public void verify_retrieval_of_correct_member_names_when_validation_context_is_broken()
+        {
+            var model = new HackTestModel();
+            var attrib = new AssertThatAttribute("false");
+
+            // correct path:
+            Assert.Equal("Value1", GetFinalMemberName(attrib, model, 0, "Value1", "Value1"));
+            Assert.Equal("Value2", GetFinalMemberName(attrib, model, 0, "Value2", "Value 2"));
+            Assert.Equal("Value3", GetFinalMemberName(attrib, model, 0, "Value3", "Value 3"));
+
+            // first issue: no member name provided (MVC <= 4)
+            Assert.Equal("Value1", GetFinalMemberName(attrib, model, 0, null, "Value1"));
+            Assert.Equal("Value2", GetFinalMemberName(attrib, model, 0, null, "Value 2"));
+            Assert.Equal("Value3", GetFinalMemberName(attrib, model, 0, null, "Value 3"));
+
+            // second issue: member name equals to display name (WebAPI 2)
+            Assert.Equal("Value2", GetFinalMemberName(attrib, model, 0, "Value 2", "Value 2"));
+            Assert.Equal("Value3", GetFinalMemberName(attrib, model, 0, "Value 3", "Value 3"));
+        }
+
+        [Fact]
+        public void return_null_in_place_of_member_name_when_it_cannot_be_unambiguously_retrieved()
+        {
+            var model = new DisplayDuplicateModel();
+            var attrib = new AssertThatAttribute("false");
+
+            Assert.Equal(null, GetFinalMemberName(attrib, model, 0, null, "duplicate"));
+        }
+
+        private static string GetFinalMemberName(ValidationAttribute attrib, object contextModel, object mamberValue, string givenMemberName, string givenDisplayName)
+        {
+            return attrib.GetValidationResult(mamberValue, new ValidationContext(contextModel)
+            {
+                MemberName = givenMemberName,
+                DisplayName = givenDisplayName
+            })?.MemberNames.Single();
+        }
+
         private static void AssertErrorMessage(string input, string output)
         {
             AssertErrorMessage(input, output, output);
@@ -440,6 +479,25 @@ private class WorkModel
             [AssertThat(HeavyExpression)]
             public int? Value { get; set; }
         }
+
+        private class HackTestModel
+        {
+            public int? Value1 { get; set; }
+
+            [Display(Name = "Value 2")]
+            public int? Value2 { get; set; }
+
+            [DisplayName("Value 3")]
+            public int? Value3 { get; set; }
+        }
+
+        private class DisplayDuplicateModel
+        {
+            [Display(Name = "duplicate")]
+            public int? Value1 { get; set; }
+            [Display(Name = "duplicate")]
+            public int? Value2 { get; set; }
+        }
     }
 
     public static class Helper

src/ExpressiveAnnotations.Tests/UtilsTest.cs

@@ -137,9 +137,9 @@ public void verify_display_names_extraction_from_given_type()
         [Fact]
         public void verify_fields_names_extraction_based_on_their_display_names() // Display attribute or DisplayName attribute used as a workaround for field name extraction in older versions of MVC where MemberName was not provided in ValidationContext
         {
-            Assert.Equal("Value1", typeof (Model).GetMemberNameByDisplayName("Value_1"));
-            Assert.Equal("Value2", typeof (Model).GetMemberNameByDisplayName("_{Value2}_"));
-            Assert.Equal("Internal", typeof (Model).GetMemberNameByDisplayName("internal"));
+            Assert.Equal("Value1", typeof (Model).GetPropertyByDisplayName("Value_1").Name);
+            Assert.Equal("Value2", typeof (Model).GetPropertyByDisplayName("_{Value2}_").Name);
+            Assert.Equal("Internal", typeof (Model).GetPropertyByDisplayName("internal").Name);
         }
 
         [Fact]

src/ExpressiveAnnotations/Attributes/ExpressiveAttribute.cs

@@ -65,6 +65,11 @@ protected ExpressiveAttribute(string expression, Func<string> errorMessageAccess
         /// </summary>        
         protected Parser Parser { get; private set; }
 
+        /// <summary>
+        ///     Gets the annotated property type.
+        /// </summary>        
+        protected Type PropertyType { get; private set; }
+
         /// <summary>
         ///     Gets the logical expression based on which specified condition is computed.
         /// </summary>
@@ -272,20 +277,30 @@ protected override ValidationResult IsValid(object value, ValidationContext vali
             catch (Exception e)
             {
                 throw new ValidationException(
-                    $"{GetType().Name}: validation applied to {validationContext.MemberName} field failed.", e);
+                    $"{GetType().Name}: validation applied to {validationContext.MemberName ?? "<member unknown>"} field failed.", e);
             }
         }
 
-        private void AdjustMemberName(ValidationContext validationContext)
+        private void AdjustMemberName(ValidationContext validationContext) // fixes for: MVC <= 4 (MemberName is not provided), WebAPI 2 (MemberName states for display name)
         {
-            if (validationContext.MemberName != null) // hack for WebAPI, where MemberName is set to display name
-                validationContext.MemberName = validationContext.ObjectType.GetMemberNameByDisplayName(validationContext.DisplayName);
+            PropertyType = null; // reset value
+            if (validationContext.MemberName == null && validationContext.DisplayName == null)
+                return;
 
-            validationContext.MemberName = validationContext.MemberName // hack for old MVC, where MemberName is not provided:
-                                           ?? validationContext.ObjectType.GetMemberNameByDisplayName(validationContext.DisplayName) // extract property using display name through Display or DisplayName annotation
-                                           ?? validationContext.DisplayName; // return DisplayName, which may contain the proper name if no Display nor DisplayName annotation exists
+            validationContext.MemberName = validationContext.MemberName ?? validationContext.DisplayName;
+            var prop = validationContext.ObjectType.GetProperty(validationContext.MemberName);
+            if (prop == null)
+            {
+                prop = validationContext.ObjectType.GetPropertyByDisplayName(validationContext.MemberName);
+                if (prop == null)
+                {
+                    validationContext.MemberName = null;
+                    return;
+                }
 
-            Debug.Assert(validationContext.MemberName != null);
+                validationContext.MemberName = prop.Name;
+            }
+            PropertyType = prop.PropertyType;
         }
 
         private string PreformatMessage(string displayName, string expression, out IList<FormatItem> items)

src/ExpressiveAnnotations/Attributes/RequiredIfAttribute.cs

@@ -45,10 +45,7 @@ public RequiredIfAttribute(string expression)
         /// <exception cref="System.InvalidOperationException"></exception>
         protected override ValidationResult IsValidInternal(object value, ValidationContext validationContext)
         {
-            var propType = validationContext.ObjectType.GetProperty(validationContext.MemberName).PropertyType;
-            if (value != null && propType.IsNonNullableValueType())
-                throw new InvalidOperationException(
-                    $"{nameof(RequiredIfAttribute)} has no effect when applied to a field of non-nullable value type '{propType.FullName}'. Use nullable '{propType.FullName}?' version instead.");
+            AssertNonValueType(value, validationContext);
 
             var isEmpty = value is string && string.IsNullOrWhiteSpace((string) value);
             if (value == null || (isEmpty && !AllowEmptyStrings))
@@ -62,5 +59,15 @@ protected override ValidationResult IsValidInternal(object value, ValidationCont
 
             return ValidationResult.Success;
         }
+
+        private void AssertNonValueType(object value, ValidationContext validationContext)
+        {
+            if (PropertyType == null)
+                return;
+
+            if (value != null && PropertyType.IsNonNullableValueType())
+                throw new InvalidOperationException(
+                    $"{nameof(RequiredIfAttribute)} has no effect when applied to a field of non-nullable value type '{PropertyType.FullName}'. Use nullable '{PropertyType.FullName}?' version instead.");
+        }
     }
 }

src/ExpressiveAnnotations/Helper.cs

@@ -250,41 +250,41 @@ public static IEnumerable<Type> GetLoadableTypes(this ITypeProvider provider)
             }
         }
 
-        public static string GetMemberNameByDisplayName(this Type type, string displayName)
+        public static PropertyInfo GetPropertyByDisplayName(this Type type, string displayName)
         {
             Debug.Assert(type != null);
             Debug.Assert(displayName != null);
 
-            return type.GetMemberNameFromDisplayAttribute(displayName) ??
-                   type.GetMemberNameFromDisplayNameAttribute(displayName);
+            return type.GetPropertyByDisplayAttribute(displayName) ??
+                   type.GetPropertyByDisplayNameAttribute(displayName);
         }
 
-        public static string GetMemberNameFromDisplayAttribute(this Type type, string displayName)
+        public static PropertyInfo GetPropertyByDisplayAttribute(this Type type, string displayName)
         {
             Debug.Assert(type != null);
             Debug.Assert(displayName != null);
 
-            // get member name from Display attribute (if such an attribute exists) based on display name
+            // get member name through Display attribute (if such an attribute exists) based on display name
             var props = type.GetProperties()
                 .Where(p => p.GetAttributes<DisplayAttribute>().Any(a => a.GetName() == displayName))
-                .Select(p => p.Name).ToList();
+                .ToList();
 
             // if there is an ambiguity, return nothing
-            return props.Count == 1 ? props.SingleOrDefault() : null;
+            return props.Count == 1 ? props.Single() : null;
         }
 
-        public static string GetMemberNameFromDisplayNameAttribute(this Type type, string displayName)
+        public static PropertyInfo GetPropertyByDisplayNameAttribute(this Type type, string displayName)
         {
             Debug.Assert(type != null);
             Debug.Assert(displayName != null);
 
-            // get member name from DisplayName attribute (if such an attribute exists) based on display name
+            // get member name through DisplayName attribute (if such an attribute exists) based on display name
             var props = type.GetProperties()
                 .Where(p => p.GetAttributes<DisplayNameAttribute>().Any(a => a.DisplayName == displayName))
-                .Select(p => p.Name).ToList();
+                .ToList();
 
             // if there is an ambiguity, return nothing
-            return props.Count == 1 ? props.SingleOrDefault() : null;
+            return props.Count == 1 ? props.Single() : null;
         }
 
         public static IEnumerable<T> GetAttributes<T>(this MemberInfo element) where T : Attribute