Convert from IEnumerable to IQueryable

Question

I'm writing access methods that query data from a database that return an IQueryable object. If something goes wrong, though, I don't want to return null, but rather an empty list. I thought I had the following working:

IQueryable<MyType> GetAllThings()
{
   IQueryable<MyType> returnList = null;

   try
   {
      // Get Things from the database
   }
   catch (Exception exception)
   {
      // Handle exceptions
   }

   if (returnList == null)
      returnList = new List<MyType>() as IQueryable<MyType>;

   return returnList
}

But it turns out that "List<MyType>() is IQueryable<MyType>" is false, so returnList stays null.

Is there a way to convert a list to an IQueryable? Or even just a way to create an empty IQueryable object?

Thanks!

Answer 1

You can call .AsQueryable() on an IEnumerable<T> sequence and it will return IQueryable<T>.

But I would seriously question why you'd want to do this. Returning an empty list in case of an exception is almost always a bad pattern - if an unknown exception is thrown, you really want to let that exception bubble up.

Joe

Answer 2

Thanks, Joe.

It's not always in that case, it was just the example case. Often I call these methods in a foreach loop and returning null causes an exception.

I do use the above pattern for my generated code, but in that case I allow the user to define a delegate for exceptions, meaning they can trap, log, and/or throw the exception as they please. I just don't want their code to break if they do with to keep the exception suppressed, which is why I wanted the empty list.

Thanks again!