Helper for classes decorated with DefaultValueAttribute

ComponentModelExtensions.cs

using System;
using System.ComponentModel;
using System.Linq.Expressions;
using System.Reflection;

namespace Extensions
{
	public static class ComponentModelExtensions
	{
		public static TProperty GetPropertyValueOrDefault<TSource, TProperty>(
			this TSource source,
			Expression<Func<TSource, TProperty>> propertyLambda)
		{
			var propInfo = GetPropertyInfo(source, propertyLambda);

			var instanceValue = propInfo.GetValue(source);
			if (instanceValue == null || ((TProperty)instanceValue).Equals(default(TProperty)))
			{
				var defaultValueAttribute = propInfo.GetCustomAttribute<DefaultValueAttribute>()?.Value;
				if (defaultValueAttribute != null)
					return (TProperty) defaultValueAttribute;
			}
			
			return (TProperty)instanceValue;
		}

		private static PropertyInfo GetPropertyInfo<TSource, TProperty>(
	TSource source,
	Expression<Func<TSource, TProperty>> propertyLambda)
		{
			Type type = typeof(TSource);

			MemberExpression member = propertyLambda.Body as MemberExpression;
			if (member == null)
				throw new ArgumentException(string.Format(
					"Expression '{0}' refers to a method, not a property.",
					propertyLambda.ToString()));

			PropertyInfo propInfo = member.Member as PropertyInfo;
			if (propInfo == null)
				throw new ArgumentException(string.Format(
					"Expression '{0}' refers to a field, not a property.",
					propertyLambda.ToString()));

			if (type != propInfo.ReflectedType &&
				!type.IsSubclassOf(propInfo.ReflectedType))
				throw new ArgumentException(string.Format(
					"Expresion '{0}' refers to a property that is not from type {1}.",
					propertyLambda.ToString(),
					type));

			return propInfo;
		}
	}
}