Added OclEnumDefaultValueAttribute

source/Ocl/Converters/EnumAttributeOclConverter.cs

@@ -33,7 +33,22 @@ public OclDocument ToDocument(OclConversionContext context, object obj)
 
         public IEnumerable<IOclElement> ToElements(OclConversionContext context, PropertyInfo? propertyInfo, object obj)
         {
-            var isDefault = Activator.CreateInstance(obj.GetType()).Equals(obj);
+            var isDefault = false;
+            var defaultValueAttributeType = typeof(OclDefaultEnumValueAttribute);
+            var defaultValueAttribute = propertyInfo?.GetCustomAttribute(defaultValueAttributeType);
+
+            if (defaultValueAttribute != null)
+            {
+                var defaultValueProperty = defaultValueAttributeType.GetProperty("DefaultValue");
+                var defaultValue = defaultValueProperty?.GetValue(defaultValueAttribute);
+
+                isDefault = Equals(obj, defaultValue);
+            }
+            else
+            {
+                isDefault = Activator.CreateInstance(obj.GetType()).Equals(obj);
+            }
+
             if (!isDefault)
                 yield return new OclAttribute(context.Namer.GetName(propertyInfo!), obj.ToString());
         }

source/Ocl/Converters/OclEnumDefaultValueAttribute.cs

@@ -0,0 +1,20 @@
+using System;
+
+namespace Octopus.Ocl.Converters
+{
+    [AttributeUsage(AttributeTargets.Property)]
+    public class OclDefaultEnumValueAttribute : Attribute
+    {
+        public OclDefaultEnumValueAttribute(object defaultValue)
+        {
+            if (!(defaultValue is Enum))
+            {
+                throw new ArgumentException("defaultValue must be an enum", nameof(defaultValue));
+            }
+
+            DefaultValue = defaultValue;
+        }
+
+        public object DefaultValue { get; }
+    }
+}

source/Tests/Converters/EnumAttributeConverterFixture.cs

@@ -0,0 +1,83 @@
+using System;
+using System.Linq;
+using FluentAssertions;
+using NUnit.Framework;
+using Octopus.Ocl;
+using Octopus.Ocl.Converters;
+
+namespace Tests.Converters
+{
+    internal class EnumAttributeConverterFixture
+    {
+        [Test]
+        public void WhenConvertingEnum_ValueIsEnumDefault_ReturnsNull()
+        {
+            var context = new OclConversionContext(new OclSerializerOptions());
+
+            var result = (OclAttribute?)new EnumAttributeOclConverter().ToElements(context, typeof(Dummy).GetProperty(nameof(Dummy.TestProperty))!, Test.Value1).SingleOrDefault();
+
+            result.Should().BeNull();
+        }
+
+        [Test]
+        public void WhenConvertingEnum_ValueIsNotEnumDefault_ReturnsValueOfProperty()
+        {
+            var context = new OclConversionContext(new OclSerializerOptions());
+
+            var result = (OclAttribute?)new EnumAttributeOclConverter().ToElements(context, typeof(Dummy).GetProperty(nameof(Dummy.TestProperty))!, Test.Value2).SingleOrDefault();
+
+            result.Should().NotBeNull();
+            result!.Value.Should().Be("Value2");
+        }
+
+        [Test]
+        public void WhenConvertingEnumWithDefaultAttribute_ValueIsEnumDefault_ReturnsValueOfProperty()
+        {
+            var context = new OclConversionContext(new OclSerializerOptions());
+
+            var result = (OclAttribute?)new EnumAttributeOclConverter().ToElements(context, typeof(DummyWithDefault).GetProperty(nameof(DummyWithDefault.TestProperty))!, Test.Value1).SingleOrDefault();
+
+            result.Should().NotBeNull();
+            result!.Value.Should().Be("Value1");
+        }
+
+        [Test]
+        public void WhenConvertingEnumWithDefaultAttribute_ValueIsNotADefault_ReturnsValueOfProperty()
+        {
+            var context = new OclConversionContext(new OclSerializerOptions());
+
+            var result = (OclAttribute?)new EnumAttributeOclConverter().ToElements(context, typeof(DummyWithDefault).GetProperty(nameof(DummyWithDefault.TestProperty))!, Test.Value2).SingleOrDefault();
+
+            result.Should().NotBeNull();
+            result!.Value.Should().Be("Value2");
+        }
+
+        [Test]
+        public void WhenConvertingEnumWithDefaultAttribute_ValueIstAttributedDefault_ReturnsNull()
+        {
+            var context = new OclConversionContext(new OclSerializerOptions());
+
+            var result = (OclAttribute?)new EnumAttributeOclConverter().ToElements(context, typeof(DummyWithDefault).GetProperty(nameof(DummyWithDefault.TestProperty))!, Test.Value3).SingleOrDefault();
+
+            result.Should().BeNull();
+        }
+
+        enum Test
+        {
+            Value1,
+            Value2,
+            Value3,
+        }
+
+        class Dummy
+        {
+            public Test TestProperty { get; } = Test.Value1;
+        }
+
+        class DummyWithDefault
+        {
+            [OclDefaultEnumValue(Test.Value3)]
+            public Test TestProperty { get; } = Test.Value1;
+        }
+    }
+}