Manpages - DBD_File_HowTo.3pm

Table of Contents


DBD:::HowTo - Guide to create DBD::File based driver


perldoc DBD:::HowTo perldoc DBI perldoc DBI::DBD perldoc DBD:::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:::HowTo perldoc DBD:::Developers


This document provides a step-by-step guide, how to create a new DBD::File based DBD. It expects that you carefully read the DBI documentation and that you’re familiar with DBI::DBD and had read and understood 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 CREATING A NEW DRIVER in DBI::DBD.

Of course, DBD::File is a DBI::DBD::SqlEngine and you surely read DBI::DBD::SqlEngine::HowTo before continuing here.


Do you have an entry in DBI’s DBD registry? For this guide, a prefix of foo_ is assumed.

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:::dr); $imp_data_size = 0; package DBD::Foo::db; use vars qw(@ISA $imp_data_size); @ISA = qw(DBD:::db); $imp_data_size = 0; package DBD::Foo::st; use vars qw(@ISA $imp_data_size); @ISA = qw(DBD:::st); $imp_data_size = 0; package DBD::Foo::Statement; use vars qw(@ISA); @ISA = qw(DBD:::Statement); package DBD::Foo::Table; use vars qw(@ISA); @ISA = qw(DBD:::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 SQL::Statement. In DBI::SQL::Nano environments, this DBD can do nothing.

Start over

Based on 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 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 SQL::Statement::Embed guide, the table is full working and you could try a start over.

User comfort

DBD::File since 0.39 consolidates all persistent meta data of a table into a single structure stored in $dbh->{f_meta}. With DBD::File version 0.41 and DBI::DBD::SqlEngine version 0.05, this consolidation moves to DBI::DBD::SqlEngine. It’s still the $dbh->{$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 User comfort in DBI::DBD::SqlEngine::HowTo.


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 DBI::DBD to ensure testing even rare cases.


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 > and Jens Rehsack < rehsack at >


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.

Author: dt

Created: 2022-02-20 Sun 14:33