Edit File: DBD::File::HowTo.3pm
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" DBD::File::HowTo \- Guide to create DBD::File based driver .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 12 \& 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 .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" This document provides a step-by-step guide, how to create a new \&\f(CW\*(C`DBD::File\*(C'\fR based \s-1DBD\s0. It expects that you carefully read the \s-1DBI\s0 documentation and that you're familiar with \s-1DBI::DBD\s0 and had read and understood DBD::ExampleP. .PP This document addresses experienced developers who are really sure that they need to invest time when writing a new \s-1DBI\s0 Driver. Writing a \s-1DBI\s0 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. .PP Those who are still reading, should be able to sing the rules of \&\*(L"\s-1CREATING\s0 A \s-1NEW\s0 \s-1DRIVER\s0\*(R" in \s-1DBI::DBD\s0. .PP Of course, DBD::File is a DBI::DBD::SqlEngine and you surely read DBI::DBD::SqlEngine::HowTo before continuing here. .SH "CREATING DRIVER CLASSES" .IX Header "CREATING DRIVER CLASSES" Do you have an entry in \s-1DBI\s0's \s-1DBD\s0 registry? For this guide, a prefix of \&\f(CW\*(C`foo_\*(C'\fR is assumed. .SS "Sample Skeleton" .IX Subsection "Sample Skeleton" .Vb 1 \& 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; .Ve .PP Tiny, eh? And all you have now is a \s-1DBD\s0 named foo which will is able to deal with temporary tables, as long as you use SQL::Statement. In DBI::SQL::Nano environments, this \s-1DBD\s0 can do nothing. .SS "Start over" .IX Subsection "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? .PP DBD::File extends DBI::DBD::SqlEngine to deal with any kind of files. In principle, the only extensions required are to the table class: .PP .Vb 1 \& 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 ); \& } .Ve .PP In case \f(CW\*(C`DBD::File::Table::open_file\*(C'\fR doesn't open the files as the driver needs that, override it! .PP .Vb 7 \& sub open_file \& { \& my ( $self, $meta, $attrs, $flags ) = @_; \& # ensure that $meta\->{f_dontopen} is set \& $self\->SUPER::open_file( $meta, $attrs, $flags ); \& # now do what ever needs to be done \& } .Ve .PP Combined with the methods implemented using the SQL::Statement::Embed guide, the table is full working and you could try a start over. .SS "User comfort" .IX Subsection "User comfort" \&\f(CW\*(C`DBD::File\*(C'\fR since \f(CW0.39\fR consolidates all persistent meta data of a table into a single structure stored in \f(CW\*(C`$dbh\->{f_meta}\*(C'\fR. With \f(CW\*(C`DBD::File\*(C'\fR version \f(CW0.41\fR and \f(CW\*(C`DBI::DBD::SqlEngine\*(C'\fR version \f(CW0.05\fR, this consolidation moves to DBI::DBD::SqlEngine. It's still the \&\f(CW\*(C`$dbh\->{$drv_prefix . "_meta"}\*(C'\fR attribute which cares, so what you learned at this place before, is still valid. .PP .Vb 3 \& 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; \& } .Ve .PP See updates at \*(L"User comfort\*(R" in DBI::DBD::SqlEngine::HowTo. .SS "Testing" .IX Subsection "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 \s-1DBI::DBD\s0 to ensure testing even rare cases. .SH "AUTHOR" .IX Header "AUTHOR" This guide is written by Jens Rehsack. DBD::File is written by Jochen Wiedmann and Jeff Zucker. .PP The module DBD::File is currently maintained by .PP H.Merijn Brand < h.m.brand at xs4all.nl > and Jens Rehsack < rehsack at googlemail.com > .SH "COPYRIGHT AND LICENSE" .IX Header "COPYRIGHT AND LICENSE" Copyright (C) 2010 by H.Merijn Brand & Jens Rehsack .PP All rights reserved. .PP You may freely distribute and/or modify this module under the terms of either the \s-1GNU\s0 General Public License (\s-1GPL\s0) or the Artistic License, as specified in the Perl \s-1README\s0 file.
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