How Can I filter by a function in silverstripe - silverstripe

Question

I want to get a list of Files that are missing for a SilverStripe report.
The filesize is not directly stored in the database, instead I have to call method getSize()
If I try to iterate through the records and just choose the empty records, I only get the first level of the file hierarchy
$all_files = File::get()->sort('FileFilename');
$list = new ArrayList();
foreach ($all_files as $file) {
$file->mysize = $file->getSize();
if($file->getSize() == "" && $file->ClassName != 'SilverStripe\Assets\Folder'){
$list->push($file);
}
}
return $list;
How can I get all the records that are empty files?

Answer 1

there are 2 parts to your question:
to filter by a function, there is:
$list = $all_files->filterByCallback(function($file) {
return $file->getSize() == "" && $file->ClassName != 'SilverStripe\Assets\Folder';
});
This is a nice shorthand but does exactly what you are doing with your foreach
For the second part of your question:
I think you misunderstood how hierarchy in SilverStripe works.
If you do File::get() you will get all files regardless of their position in the hierarchy.
So you already have what you want I think. But if you only want files at the top level, you have to do $files = File::get()->filter(["ParentID" => 0]) and if you want a tree, then do a recursive loop with $file->Children().
Or you do what you've already done: fetch all of them, and then build a tree yourself based on the ParentID.