1DBD::File::HowTo(3)   User Contributed Perl Documentation  DBD::File::HowTo(3)
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3
4

NAME

6       DBD::File::HowTo - Guide to create DBD::File based driver
7

SYNOPSIS

9         perldoc DBD::File::HowTo
10         perldoc DBI
11         perldoc DBI::DBD
12         perldoc DBD::File::Developers
13         perldoc DBI::DBD::SqlEngine::Developers
14         perldoc DBI::DBD::SqlEngine
15         perldoc SQL::Eval
16         perldoc DBI::DBD::SqlEngine::HowTo
17         perldoc SQL::Statement::Embed
18         perldoc DBD::File
19         perldoc DBD::File::HowTo
20         perldoc DBD::File::Developers
21

DESCRIPTION

23       This document provides a step-by-step guide, how to create a new
24       "DBD::File" based DBD. It expects that you carefully read the DBI
25       documentation and that you're familiar with DBI::DBD and had read and
26       understood DBD::ExampleP.
27
28       This document addresses experienced developers who are really sure that
29       they need to invest time when writing a new DBI Driver. Writing a DBI
30       Driver is neither a weekend project nor an easy job for hobby coders
31       after work. Expect one or two man-month of time for the first start.
32
33       Those who are still reading, should be able to sing the rules of
34       "CREATING A NEW DRIVER" in DBI::DBD.
35
36       Of course, DBD::File is a DBI::DBD::SqlEngine and you surely read
37       DBI::DBD::SqlEngine::HowTo before continuing here.
38

CREATING DRIVER CLASSES

40       Do you have an entry in DBI's DBD registry? For this guide, a prefix of
41       "foo_" is assumed.
42
43   Sample Skeleton
44           package DBD::Foo;
45
46           use strict;
47           use warnings;
48           use vars qw(@ISA $VERSION);
49           use base qw(DBD::File);
50
51           use DBI ();
52
53           $VERSION = "0.001";
54
55           package DBD::Foo::dr;
56
57           use vars qw(@ISA $imp_data_size);
58
59           @ISA = qw(DBD::File::dr);
60           $imp_data_size = 0;
61
62           package DBD::Foo::db;
63
64           use vars qw(@ISA $imp_data_size);
65
66           @ISA = qw(DBD::File::db);
67           $imp_data_size = 0;
68
69           package DBD::Foo::st;
70
71           use vars qw(@ISA $imp_data_size);
72
73           @ISA = qw(DBD::File::st);
74           $imp_data_size = 0;
75
76           package DBD::Foo::Statement;
77
78           use vars qw(@ISA);
79
80           @ISA = qw(DBD::File::Statement);
81
82           package DBD::Foo::Table;
83
84           use vars qw(@ISA);
85
86           @ISA = qw(DBD::File::Table);
87
88           1;
89
90       Tiny, eh? And all you have now is a DBD named foo which will be able to
91       deal with temporary tables, as long as you use SQL::Statement. In
92       DBI::SQL::Nano environments, this DBD can do nothing.
93
94   Start over
95       Based on DBI::DBD::SqlEngine::HowTo, we're now having a driver which
96       could do basic things. Of course, it should now derive from DBD::File
97       instead of DBI::DBD::SqlEngine, shouldn't it?
98
99       DBD::File extends DBI::DBD::SqlEngine to deal with any kind of files.
100       In principle, the only extensions required are to the table class:
101
102           package DBD::Foo::Table;
103
104           sub bootstrap_table_meta
105           {
106               my ( $self, $dbh, $meta, $table ) = @_;
107
108               # initialize all $meta attributes which might be relevant for
109               # file2table
110
111               return $self->SUPER::bootstrap_table_meta($dbh, $meta, $table);
112           }
113
114           sub init_table_meta
115           {
116               my ( $self, $dbh, $meta, $table ) = @_;
117
118               # called after $meta contains the results from file2table
119               # initialize all missing $meta attributes
120
121               $self->SUPER::init_table_meta( $dbh, $meta, $table );
122           }
123
124       In case "DBD::File::Table::open_file" doesn't open the files as the
125       driver needs that, override it!
126
127           sub open_file
128           {
129               my ( $self, $meta, $attrs, $flags ) = @_;
130               # ensure that $meta->{f_dontopen} is set
131               $self->SUPER::open_file( $meta, $attrs, $flags );
132               # now do what ever needs to be done
133           }
134
135       Combined with the methods implemented using the SQL::Statement::Embed
136       guide, the table is full working and you could try a start over.
137
138   User comfort
139       "DBD::File" since 0.39 consolidates all persistent meta data of a table
140       into a single structure stored in "$dbh->{f_meta}". With "DBD::File"
141       version 0.41 and "DBI::DBD::SqlEngine" version 0.05, this consolidation
142       moves to DBI::DBD::SqlEngine. It's still the "$dbh->{$drv_prefix .
143       "_meta"}" attribute which cares, so what you learned at this place
144       before, is still valid.
145
146           sub init_valid_attributes
147           {
148               my $dbh = $_[0];
149
150               $dbh->SUPER::init_valid_attributes ();
151
152               $dbh->{foo_valid_attrs} = { ... };
153               $dbh->{foo_readonly_attrs} = { ...  };
154
155               $dbh->{foo_meta} = "foo_tables";
156
157               return $dbh;
158           }
159
160       See updates at "User comfort" in DBI::DBD::SqlEngine::HowTo.
161
162   Testing
163       Now you should have your own DBD::File based driver. Was easy, wasn't
164       it?  But does it work well?  Prove it by writing tests and remember to
165       use dbd_edit_mm_attribs from DBI::DBD to ensure testing even rare
166       cases.
167

AUTHOR

169       This guide is written by Jens Rehsack. DBD::File is written by Jochen
170       Wiedmann and Jeff Zucker.
171
172       The module DBD::File is currently maintained by
173
174       H.Merijn Brand < h.m.brand at xs4all.nl > and Jens Rehsack  < rehsack
175       at googlemail.com >
176
178       Copyright (C) 2010 by H.Merijn Brand & Jens Rehsack
179
180       All rights reserved.
181
182       You may freely distribute and/or modify this module under the terms of
183       either the GNU General Public License (GPL) or the Artistic License, as
184       specified in the Perl README file.
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188perl v5.32.1                      2021-01-27               DBD::File::HowTo(3)
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