Question

I have an extension method called ToListIfNotNullOrEmpty(), which is hitting the DB twice, instead of once. The first time it returns one result, the second time it returns all the correct results.

I’m pretty sure the first time it hits the database, is when the .Any() method is getting called.

here’s the code.

public static IList<T> ToListIfNotNullOrEmpty<T>(this IEnumerable<T> value)
{
    if (value.IsNullOrEmpty())
    {
        return null;
    }
    if (value is IList<T>)
    {
        return (value as IList<T>);
    }
    return new List<T>(value);
}

public static bool IsNullOrEmpty<T>(this IEnumerable<T> value)
{
    if (value != null)
    {
        return !value.Any();
    }
    return true;
}

I’m hoping to refactor it so that, before the .Any() method is called, it actually enumerates through the entire list.

If i do the following, only one DB call is made, because the list is already enumerated.

var pewPew = (from x in whatever
              select x)
             .ToList()   // This enumerates.
             .ToListIsNotNullOrEmpty();  // This checks the enumerated result.

I sorta don’t really want to call ToList() then my extension method.
Any ideas, folks?

Answer 1

I confess that I see little point in this method. Surely if you simply do a ToList(), a check to see if the list is empty suffices as well. It’s arguably harder to handle the null result when you expect a list because then you always have to check for null before you iterate over it.

I think that:

 var query = (from ...).ToList();
 if (query.Count == 0) {
     ...
 }

works as well and is less burdensome than

var query = (from ...).ToListIfNotNullOrEmpty();
if (query == null) {
   ...
}

and you don’t have to implement (and maintain) any code.