DBD::File::HowTo - Online Linux Manual PageSection : 3pm
Updated : 2020-11-08
Source : perl v5.32.0
Note : User Contributed Perl Documentation
NAMEDBD::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
DESCRIPTIONThis 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 CLASSESDo 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 overBased 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.
TestingNow 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.
AUTHORThis 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 LICENSECopyright (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. 0
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