I've been trying to write a recursive function to generate a hash of hashes with little luck. (Recursive functions seem to be my nemesis as of late...) I'm parsing some hierarchical data from a database and trying to display it in a Win32::GUI::Treeview.

I've written a recursive function to populate the TreeView given input that looks like this:

Item1 => {
    SubItem1 => {
        SubSubItem1 => 1,
        SubSubItem2 => 1,
        SubSubItem3 => 1,
    },
    SubItem2 => {
        SubSubItem1 => 1,
        SubSubItem2 => 1,
        SubSubItem3 => 1,
    },
},
Item2 => {
...
[download]

Which works great and looks like this:

sub hashref_to_treeview {
    my $hashref = shift;
    my $treeview = shift; # Win32::GUI::Treeview object
    my $parent_node = shift || 0;
    
    return unless ref($hashref) eq 'HASH';
    
    for my $node ( sort keys %$hashref ) {
        my $new_node = $treeview->InsertItem(-text => $node, -parent =
+> $parent_node);
        hashref_to_treeview($$hashref{$node}, $treeview, $new_node);
    }
}
[download]

However, I'm having trouble getting the data out of the database to look like the input up there to feed into hashref_to_treeview. I was able to replicate the behavior I would like with a nasty set of nested foreach loops, but after finishing it looked terrible to maintain and decidedly un-perl-ish. I've summarized the flow below in pseudo-perl.

my $id = 1;
my $data = {};
my $table1_results = $dbh->selectall_arrayref('SELECT field1 FROM tabl
+e1 WHERE id = ?', {Slice => {}}, $id);
foreach my $field1 (@$table1_results) {
    $data->{$id}->{$table1_results->{field_of_interest}} = undef;
    my $table2_results = $dbh->selectall_arrayref('SELECT field2 FROM 
+table2 WHERE field1 = ?', {Slice => {}}, $field1->{field1});
    foreach my $field2 (@$table2_results) {
        $data->{$id}->{$table1_results->{field_of_interest}}->{$table2
+_results->{field_of_interest}} = undef;
        ...
    }
}
[download]

I set up a slightly less ugly set of joins on the tables in question to return the values like this:

parent   child1   child2   child3
-------- -------- -------- --------
value1   value2   value3   value4
value1   value2a  value3   (null)
...
[download]

This seems a bit easier since the SQL changes for each level of recursion which I'd have to deal with in the function. The join's output could be returned with DBI's selectall_arrayref and then I can just recurse through each array. But I've gotten stuck on how to make that data look like the structure above. My most recent attempt looked something like this:

sub recursion_test {
    my $array = shift;
    
    my @results;
    while(@$array > 1){
        push @results, recursion_test($array);
    }
    return [$$array[0], undef];
}
[download]

Which doesn't work as well as I'd hoped and leads me to my question: How can I return data structures through recursion so I can build the hash above? Also, any other suggestions for a more painless way to do this would be welcomed!

Thanks in advance for your help!

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