POE::Component::DBIAgent::Helper(3) DBI Query Helper for DBIAgent


 use Socket qw/:crlf/;
 use POE qw/Filter::Line Wheel::Run Component::DBIAgent::Helper/;
 sub _start {
     my $helper = POE::Wheel::Run ->new(
             Program     => sub {
             StdoutEvent => 'db_reply',
             StderrEvent => 'remote_stderr',
             ErrorEvent  => 'error',
             StdinFilter => POE::Filter::Line->new(),
             StdoutFilter => POE::Filter::Line->new( Literal => CRLF),
             StderrFilter => POE::Filter::Line->new(),
      or carp "Can't create new DBIAgent::Helper: $!\n";
 sub query {
      my ($self, $query, $package, $state, @rest) = @_;
      $self->{helper}->put(join '|', $query, $package, $state, @rest);
 sub db_reply {
    my ($kernel, $self, $heap, $input) = @_[KERNEL, OBJECT, HEAP, ARG0];
    # $input is either the string 'EOF' or a Storable object.


This is our helper routine for DBIAgent. It accepts queries on STDIN, and returns the results on STDOUT. Queries are returned on a row-by-row basis, followed by a row consisting of the string 'EOF'.

Each row is the return value of $sth->fetch, which is an arrayref. This row is then passed to Storable for transport, and printed to STDOUT. HOWEVER, Storable uses newlines (``\n'') in its serialized strings, so the Helper is designed to use the ``network newline'' pair CR LF as the line terminator for STDOUT.

When fetch() returns undef, one final row is returned to the calling state: the string 'EOF'. Sessions should test for this value FIRST when being invoked with input from a query.


The Helper has one public subroutine, called "run()", and is invoked with two parameters:
An arrayref of parameters to pass to DBI->connect (usually a dsn, username, and password).
The Queries.
A hashref of the form Query_Name => ``$SQL''. See POE::Component::DBIAgent for details.


I have NO idea what to do about handling signals intelligently. Specifically, under some circumstances, Oracle will refuse to acknowledge SIGTERM (presumably since its libraries are non-reentrant) so sometimes SIGKILL is required to terminate a Helper process.


This module has been fine-tuned and packaged by Rob Bloodgood <[email protected]>. However, most of the code came directly from Fletch <[email protected]>, either directly (Po:Co:DBIAgent:Queue) or via his ideas. Thank you, Fletch!

However, I own all of the bugs.

This module is free software; you may redistribute it and/or modify it under the same terms as Perl itself.