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.