I'm a little bit confused about the way DBI works when I re-use a prepared statement handle inside a while loop. Here's what I mean (table contains a set of tree structure data where elements refer to a parent_id):

my $prepared_handle = $dbh->prepare('SELECT * FROM table WHERE parent_
+id = ?');

:
:
:
get_children(0);

sub get_children {
  my $parent_id = shift;

  $executed_handle = $prepared_handle->execute($parent_id);
  while (my $pointer = $executed_handle->fetchrow_hashref) {
    $results .= $pointer->{id}."\n";
    get_children($pointer->{parent_id});
  }
}

[download]

This sort of code doesn't seem to work because the nested call to get_children() appears to be overwriting the previous query. I'm getting:

Top level A
Top level B
  Second Level A
  Second Level B

[download]

and then it stops, instead of continuing like so:

Top level A
Top level B
  Second Level A
  Second Level B
Top level C
Top level D

[download]

Now this isn't a major problem, I can just re-prepare the $prepared_handle inside get_children() each time instead of using a globally prepared one, but this is less obviously efficient.

Is there an efficient way around this or is this just a limitation of the DBI interface?

(This is on mysql if it makes a difference)

Cheers
MattLG

In reply to Nesting prepared DBI handles by MattLG

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