# DBD::File::HowTo - phpMan

## NAME
    [DBD::File::HowTo] - Guide to create [DBD::File] based driver

## 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]

## DESCRIPTION
    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.

## 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];

        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 [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].

  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 [DBI::DBD] to ensure testing even rare cases.

## 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 >

## 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.