Why Generic Casting is not working on this section of code?

Question

IQueryable<T> IS3Repository.FindAllBuckets<T>()
{
  IQueryable<object> list = _repository.GetAllBuckets().Cast<object>().AsQueryable();
  return list == null ? default(T) : (T)list;
}

This is the error: Error 3 Cannot implicitly convert type 'T' to 'System.Linq.IQueryable'. An explicit conversion exists (are you missing a cast?)

I am implementing this interface:

 IQueryable<T> FindAllBuckets<T>();

What is the problem?

This is what I have tried:

1. IQueryable<T> IS3Repository.FindAllBuckets<T>()
   {
       IQueryable<object> list = _repository
                                 .GetAllBuckets()
                                 .Cast<object>().AsQueryable();
   
   
   return list == null ? list.DefaultIfEmpty().AsQueryable() : list; }
   
   
   

Answer 1

Try this:

IQueryable<T> IS3Repository.FindAllBuckets<T>()
{
    IQueryable<T> list = _repository
                         .GetAllBuckets()
                         .Cast<T>()
                         .AsQueryable();

    return list ?? new List<T>().AsQueryable();
}

The main problem with your original approach is that you were trying to return an instance of T rather than an instance of IQueryable<T>.

Answer 2

You're casting list to T but the return value of FindAllBuckets is of type IQueryable<T>.

Depending on the return type of _repository.GetAllBuckets(), this should work:

IQueryable<T> IS3Repository.FindAllBuckets<T>()
{
    return _repository.GetAllBuckets()
                      .Cast<T>()
                      .AsQueryable();
}