C# How to turn all empty lists inside object into null

Question

First of all, i'm aware of the popular advice that you should avoid returning empty lists at all. But as of now, due to a myriad of reasons, i'm met with no other choice but to do just that.

What i'm asking is how do I iterate through the properties of an object (probably through Reflection), take whatever lists I may find and check if it's empty. If so, then turn it into null, otherwise, leave it be.

I'm stuck with the following code, which includes somewhat of a try with Reflection:

private static void IfEmptyListThenNull<T>(T myObject)
{
    foreach (PropertyInfo propertyInfo in myObject.GetType().GetProperties())
    {
        if (propertyInfo.PropertyType.IsGenericType && propertyInfo.PropertyType.GetGenericTypeDefinition() == typeof(List<>))
        {
            //How to know if the list i'm checking is empty, and set its value to null
        }
    }
}

https://stackoverflow.com/questions/1043755/c-sharp-generic-list-t-how-to-get-the-type-of-t shows how to check for list... then calling `.Count` property either through `dynamic` or reflection should not be a problem... — Alexei Levenkov, Mar 07 '19 at 17:44
The answer you linked to says “NEVER return null when returning a collection or enumerable. ALWAYS return an empty enumerable/collection ...”; how did you interpret this to mean “avoid returning empty lists”? — Dour High Arch, Mar 07 '19 at 18:07

Eugene Chybisov · Accepted Answer · 2019-03-07T18:16:18.550

This should work for you, just use GetValue method and cast value to IList, then check for emptiness and set this value via SetValue to null.

private static void IfEmptyListThenNull<T>(T myObject)
        {
            foreach (PropertyInfo propertyInfo in myObject.GetType().GetProperties())
            {
                if (propertyInfo.PropertyType.IsGenericType && propertyInfo.PropertyType.GetGenericTypeDefinition() == typeof(List<>))
                {
                    if (((IList)propertyInfo.GetValue(myObject, null)).Count == 0)
                    {
                        propertyInfo.SetValue(myObject, null);
                    }
                }
            }
        }

C# How to turn all empty lists inside object into null

1 Answers1