$listings = Listing::has('photos')->get();

// fetch all the listings, eagerly loading the photos relationship
$listings = Listing::with('photos')->get();

foreach ($listings as $key => $listing)
{
    // if the listing has photos, remove it from the collection
    if (count($listing->photos) != 0)
    {
        unset($listings[$key]);
    }
}

$users = $users->filter(function($user)
{
    if($user->isAdmin())
    {
        return $user;
    }
});

$listings = $listings->filter(function($listing)
{
    // Keep listings with no photos
    if (count($listing->photos) == 0)
    {
        return $listing;
    }
});