# phpman > man > DBD::File::HowTo

## NAME
    [DBD::File::HowTo](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3AHowTo/markdown) - Guide to create [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown) based driver

## SYNOPSIS
      perldoc [DBD::File::HowTo](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3AHowTo/markdown)
      perldoc DBI
      perldoc [DBI::DBD](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD/markdown)
      perldoc [DBD::File::Developers](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3ADevelopers/markdown)
      perldoc [DBI::DBD::SqlEngine::Developers](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3ADevelopers/markdown)
      perldoc [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown)
      perldoc [SQL::Eval](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AEval/markdown)
      perldoc [DBI::DBD::SqlEngine::HowTo](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3AHowTo/markdown)
      perldoc [SQL::Statement::Embed](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement%3A%3AEmbed/markdown)
      perldoc [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown)
      perldoc [DBD::File::HowTo](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3AHowTo/markdown)
      perldoc [DBD::File::Developers](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3ADevelopers/markdown)

## DESCRIPTION
    This document provides a step-by-step guide, how to create a new "[DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown)" based DBD. It
    expects that you carefully read the DBI documentation and that you're familiar with [DBI::DBD](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD/markdown) and
    had read and understood [DBD::ExampleP](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AExampleP/markdown).

    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](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD/markdown).

    Of course, [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown) is a [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) and you surely read [DBI::DBD::SqlEngine::HowTo](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3AHowTo/markdown)
    before continuing here.

## CREATING DRIVER CLASSES
    Do you have an entry in DBI's DBD registry? For this guide, a prefix of "foo_" is assumed.

### Sample Skeleton
        package [DBD::Foo](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFoo/markdown);

        use strict;
        use warnings;
        use vars qw(@ISA $VERSION);
        use base qw([DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown));

        use DBI ();

        $VERSION = "0.001";

        package [DBD::Foo::dr](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFoo%3A%3Adr/markdown);

        use vars qw(@ISA $imp_data_size);

        @ISA = qw([DBD::File::dr](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3Adr/markdown));
        $imp_data_size = 0;

        package [DBD::Foo::db](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFoo%3A%3Adb/markdown);

        use vars qw(@ISA $imp_data_size);

        @ISA = qw([DBD::File::db](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3Adb/markdown));
        $imp_data_size = 0;

        package [DBD::Foo::st](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFoo%3A%3Ast/markdown);

        use vars qw(@ISA $imp_data_size);

        @ISA = qw([DBD::File::st](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3Ast/markdown));
        $imp_data_size = 0;

        package [DBD::Foo::Statement](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFoo%3A%3AStatement/markdown);

        use vars qw(@ISA);

        @ISA = qw([DBD::File::Statement](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3AStatement/markdown));

        package [DBD::Foo::Table](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFoo%3A%3ATable/markdown);

        use vars qw(@ISA);

        @ISA = qw([DBD::File::Table](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3ATable/markdown));

        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](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement/markdown). In [DBI::SQL::Nano](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ASQL%3A%3ANano/markdown) environments, this DBD can do
    nothing.

### Start over
    Based on [DBI::DBD::SqlEngine::HowTo](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3AHowTo/markdown), we're now having a driver which could do basic things. Of
    course, it should now derive from [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown) instead of [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown), shouldn't it?

    [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown) extends [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) to deal with any kind of files. In principle, the only
    extensions required are to the table class:

        package [DBD::Foo::Table](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFoo%3A%3ATable/markdown);

        sub bootstrap_table_meta
        {
            my ( $self, $dbh, $meta, $table ) = @_;

            # initialize all $meta attributes which might be relevant for
            # file2table

            return $self->[SUPER::bootstrap_table_meta](https://www.chedong.com/phpMan.php/perldoc/SUPER%3A%3Abootstraptablemeta/markdown)($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](https://www.chedong.com/phpMan.php/perldoc/SUPER%3A%3Ainittablemeta/markdown)( $dbh, $meta, $table );
        }

    In case "[DBD::File::Table::open_file](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3ATable%3A%3Aopenfile/markdown)" 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](https://www.chedong.com/phpMan.php/perldoc/SUPER%3A%3Aopenfile/markdown)( $meta, $attrs, $flags );
            # now do what ever needs to be done
        }

    Combined with the methods implemented using the [SQL::Statement::Embed](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement%3A%3AEmbed/markdown) guide, the table is full
    working and you could try a start over.

### User comfort
    "[DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown)" since 0.39 consolidates all persistent meta data of a table into a single structure
    stored in "$dbh->{f_meta}". With "[DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown)" version 0.41 and "[DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown)" version
    0.05, this consolidation moves to [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown). It's still the "$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](https://www.chedong.com/phpMan.php/perldoc/SUPER%3A%3Ainitvalidattributes/markdown) ();

            $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](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3AHowTo/markdown).

### Testing
    Now you should have your own [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown) 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](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD/markdown) to ensure
    testing even rare cases.

## AUTHOR
    This guide is written by Jens Rehsack. [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown) is written by Jochen Wiedmann and Jeff Zucker.

    The module [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown) is currently maintained by

    H.Merijn Brand < h.m.brand at xs4all.nl > and Jens Rehsack < rehsack at googlemail.com >

## 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.