Don't fallback to default mapping when property is ignored

Resolves #81

src/Dapper.FluentMap/TypeMaps/FluentTypeMap.cs

@@ -48,6 +48,14 @@ private static PropertyInfo GetPropertyInfo(Type type, string columnName)
                         TypePropertyMapCache.TryAdd(cacheKey, propertyMap.PropertyInfo);
                         return propertyMap.PropertyInfo;
                     }
+#if !NETSTANDARD1_3
+                    else
+                    {
+                        var ignoredPropertyInfo = new IgnoredPropertyInfo();
+                        TypePropertyMapCache.TryAdd(cacheKey, ignoredPropertyInfo);
+                        return ignoredPropertyInfo;
+                    }
+#endif
                 }
             }
 

src/Dapper.FluentMap/TypeMaps/IgnoredPropertyInfo.cs

@@ -0,0 +1,28 @@
+#if !NETSTANDARD1_3
+using System;
+using System.Globalization;
+using System.Reflection;
+
+namespace Dapper.FluentMap.TypeMaps
+{
+    internal class IgnoredPropertyInfo : PropertyInfo
+    {
+        public override Type PropertyType => throw new NotImplementedException();
+        public override PropertyAttributes Attributes => throw new NotImplementedException();
+        public override bool CanRead => throw new NotImplementedException();
+        public override bool CanWrite => throw new NotImplementedException();
+        public override string Name => throw new NotImplementedException();
+        public override Type DeclaringType => throw new NotImplementedException();
+        public override ParameterInfo[] GetIndexParameters() => throw new NotImplementedException();
+        public override Type ReflectedType => throw new NotImplementedException();
+        public override MethodInfo[] GetAccessors(bool nonPublic) => throw new NotImplementedException();
+        public override object[] GetCustomAttributes(bool inherit) => throw new NotImplementedException();
+        public override object[] GetCustomAttributes(Type attributeType, bool inherit) => throw new NotImplementedException();
+        public override MethodInfo GetGetMethod(bool nonPublic) => throw new NotImplementedException();
+        public override MethodInfo GetSetMethod(bool nonPublic) => throw new NotImplementedException();
+        public override bool IsDefined(Type attributeType, bool inherit) => throw new NotImplementedException();
+        public override object GetValue(object obj, BindingFlags invokeAttr, Binder binder, object[] index, CultureInfo culture) => throw new NotImplementedException();
+        public override void SetValue(object obj, object value, BindingFlags invokeAttr, Binder binder, object[] index, CultureInfo culture) => throw new NotImplementedException();
+    }
+}
+#endif

src/Dapper.FluentMap/TypeMaps/MultiTypeMap.cs

@@ -103,6 +103,14 @@ public SqlMapper.IMemberMap GetMember(string columnName)
                     var result = mapper.GetMember(columnName);
                     if (result != null)
                     {
+#if !NETSTANDARD1_3
+                        if (result is IgnoredPropertyInfo)
+                        {
+                            // The property is explicitly ignored, 
+                            // return null to prevent falling back to default type map of Dapper.
+                            return null;
+                        }
+#endif
                         return result;
                     }
                 }