Extending IEnumerable With Reflection To Create A Custom Distinct Method

Reflection is a great tool when it comes to handling the information at runtime. I found this solution below to be suitable in one of my applications because I wanted something that I could easily adapt.

The implementation of the method below looks for both public and private fields and properties.

namespace MyNamespace
{
static class Extensions
{
public static IEnumerable<T> DistinctBy<T, Tkey>(this IEnumerable<T> @this, string binding)
{
string[] PropertyNames = binding.Split('.');
IList<Tkey> PropertyValues = new List<Tkey>();
IList<T> DistinctList = new List<T>();
//
foreach (var item in @this)
{
//get key
object Key = item;
foreach (var Property in PropertyNames)
{
Type keyType = Key.GetType();
//Check for property first - public and private
FieldInfo fieldInfo = keyType.GetField(Property, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
PropertyInfo propertyInfo = keyType.GetProperty(Property, BindingFlags.Public | BindingFlags.NonPublic |BindingFlags.Instance);
if (propertyInfo != null)
{
Key = propertyInfo.GetValue(Key);
}
else if (fieldInfo != null)
{
Key = fieldInfo.GetValue(Key);
}
else {
Key = null;
}
}
if (Key == null) {
DistinctList.Add(item);
}
else if (PropertyValues.Where(x => x.Equals(Key)).Count() == 0)
{
PropertyValues.Add((Tkey)Key);
DistinctList.Add(item);
}
}
return DistinctList;
}
}

Let’s create a product class that has a Price. We aim to easily create a list with unique “parameters” that will be defined in a string.

class Price
{
public double Value { get; set; }
}
class Product
{
public string Name { get; set; }
public Price Price { get; set; }
private int NoPrice;
}
class Program
{
static void Main(string[] args)
{
List<Product> Products = new List<Product>
{
new Product{ Name = "Product1", Price = new Price{ Value = 100} },
new Product{ Name = "Product2", Price = new Price{ Value = 100} },
new Product{ Name = "Product3", Price = new Price{ Value = 200} }
};
// will result 1 item, NoPrice default for all is 0
var DistinctProducts1 = Products.DistinctBy<Product, int>("NoPrice");
// will result 3 items, no such key is found
var DistinctProducts2 = Products.DistinctBy<Product, int>("NoPrice.Test");
// will result 2 items - Value is 100 for 2 of them
var DistinctProducts3 = Products.DistinctBy<Product, int>("Price.Value");
}
}
}