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Edit File: HowTo.pod
=head1 NAME DBD::File::HowTo - Guide to create DBD::File based driver =head1 SYNOPSIS perldoc DBD::File::HowTo perldoc DBI perldoc DBI::DBD perldoc DBD::File::Developers perldoc DBI::DBD::SqlEngine::Developers perldoc DBI::DBD::SqlEngine perldoc SQL::Eval perldoc DBI::DBD::SqlEngine::HowTo perldoc SQL::Statement::Embed perldoc DBD::File perldoc DBD::File::HowTo perldoc DBD::File::Developers =head1 DESCRIPTION This document provides a step-by-step guide, how to create a new C<DBD::File> based DBD. It expects that you carefully read the L<DBI> documentation and that you're familiar with L<DBI::DBD> and had read and understood L<DBD::ExampleP>. This document addresses experienced developers who are really sure that they need to invest time when writing a new DBI Driver. Writing a DBI Driver is neither a weekend project nor an easy job for hobby coders after work. Expect one or two man-month of time for the first start. Those who are still reading, should be able to sing the rules of L<DBI::DBD/CREATING A NEW DRIVER>. Of course, DBD::File is a DBI::DBD::SqlEngine and you surely read L<DBI::DBD::SqlEngine::HowTo> before continuing here. =head1 CREATING DRIVER CLASSES Do you have an entry in DBI's DBD registry? For this guide, a prefix of C<foo_> is assumed. =head2 Sample Skeleton package DBD::Foo; use strict; use warnings; use vars qw(@ISA $VERSION); use base qw(DBD::File); use DBI (); $VERSION = "0.001"; package DBD::Foo::dr; use vars qw(@ISA $imp_data_size); @ISA = qw(DBD::File::dr); $imp_data_size = 0; package DBD::Foo::db; use vars qw(@ISA $imp_data_size); @ISA = qw(DBD::File::db); $imp_data_size = 0; package DBD::Foo::st; use vars qw(@ISA $imp_data_size); @ISA = qw(DBD::File::st); $imp_data_size = 0; package DBD::Foo::Statement; use vars qw(@ISA); @ISA = qw(DBD::File::Statement); package DBD::Foo::Table; use vars qw(@ISA); @ISA = qw(DBD::File::Table); 1; Tiny, eh? And all you have now is a DBD named foo which will be able to deal with temporary tables, as long as you use L<SQL::Statement>. In L<DBI::SQL::Nano> environments, this DBD can do nothing. =head2 Start over Based on L<DBI::DBD::SqlEngine::HowTo>, we're now having a driver which could do basic things. Of course, it should now derive from DBD::File instead of DBI::DBD::SqlEngine, shouldn't it? DBD::File extends DBI::DBD::SqlEngine to deal with any kind of files. In principle, the only extensions required are to the table class: package DBD::Foo::Table; sub bootstrap_table_meta { my ( $self, $dbh, $meta, $table ) = @_; # initialize all $meta attributes which might be relevant for # file2table return $self->SUPER::bootstrap_table_meta($dbh, $meta, $table); } sub init_table_meta { my ( $self, $dbh, $meta, $table ) = @_; # called after $meta contains the results from file2table # initialize all missing $meta attributes $self->SUPER::init_table_meta( $dbh, $meta, $table ); } In case C<DBD::File::Table::open_file> doesn't open the files as the driver needs that, override it! sub open_file { my ( $self, $meta, $attrs, $flags ) = @_; # ensure that $meta->{f_dontopen} is set $self->SUPER::open_file( $meta, $attrs, $flags ); # now do what ever needs to be done } Combined with the methods implemented using the L<SQL::Statement::Embed> guide, the table is full working and you could try a start over. =head2 User comfort C<DBD::File> since C<0.39> consolidates all persistent meta data of a table into a single structure stored in C<< $dbh->{f_meta} >>. With C<DBD::File> version C<0.41> and C<DBI::DBD::SqlEngine> version C<0.05>, this consolidation moves to L<DBI::DBD::SqlEngine>. It's still the C<< $dbh->{$drv_prefix . "_meta"} >> attribute which cares, so what you learned at this place before, is still valid. sub init_valid_attributes { my $dbh = $_[0]; $dbh->SUPER::init_valid_attributes (); $dbh->{foo_valid_attrs} = { ... }; $dbh->{foo_readonly_attrs} = { ... }; $dbh->{foo_meta} = "foo_tables"; return $dbh; } See updates at L<DBI::DBD::SqlEngine::HowTo/User comfort>. =head2 Testing Now you should have your own DBD::File based driver. Was easy, wasn't it? But does it work well? Prove it by writing tests and remember to use dbd_edit_mm_attribs from L<DBI::DBD> to ensure testing even rare cases. =head1 AUTHOR This guide is written by Jens Rehsack. DBD::File is written by Jochen Wiedmann and Jeff Zucker. The module DBD::File is currently maintained by H.Merijn Brand < h.m.brand at xs4all.nl > and Jens Rehsack < rehsack at googlemail.com > =head1 COPYRIGHT AND LICENSE Copyright (C) 2010 by H.Merijn Brand & Jens Rehsack All rights reserved. You may freely distribute and/or modify this module under the terms of either the GNU General Public License (GPL) or the Artistic License, as specified in the Perl README file. =cut