1ORLite::Migrate(3) User Contributed Perl Documentation ORLite::Migrate(3)
2
6 ORLite::Migrate - Extremely light weight SQLite-specific schema
7 migration
8
10 # Build your ORM class using a patch timeline
11 # stored in the shared files directory.
12 use ORLite::Migrate {
13 create => 1,
14 file => 'sqlite.db',
15 timeline => File::Spec->catdir(
16 File::ShareDir::module_dir('My::Module'), 'patches',
17 ),
18 user_version => 8,
19 };
20 # migrate-1.pl - A trivial schema patch
22 #!/usr/bin/perl
23 use strict;
25 use DBI ();
26 # Locate the SQLite database
28 my $file = <STDIN>;
29 chomp($file);
30 unless ( -f $file and -w $file ) {
31 die "SQLite file $file does not exist";
32 }
33 # Connect to the SQLite database
35 my $dbh = DBI->connect("dbi:SQLite(RaiseError=>1):$file");
36 unless ( $dbh ) {
37 die "Failed to connect to $file";
38 }
39 $dbh->do( <<'END_SQL' );
41 create table foo (
42 id integer not null primary key,
43 name varchar(32) not null
44 )
45 END_SQL
46
48 SQLite is a light weight single file SQL database that provides an
49 excellent platform for embedded storage of structured data.
50 ORLite is a light weight single class Object-Relational Mapper (ORM)
52 system specifically designed for (and limited to only) work with
53 SQLite.
54 ORLite::Migrate is a light weight single class Database Schema
56 Migration enhancement for ORLite.
57 It provides a simple implementation of schema versioning within the
59 SQLite database using the built-in "user_version" pragma (which is set
60 to zero by default).
61 When setting up the ORM class, an additional "timeline" parameter is
63 provided, which should be either a monolithic timeline class, or a
64 directory containing standalone migration scripts.
65 A "timeline" is a set of revisioned schema changed, to be applied in
67 order and representing the evolution of the database schema over time.
68 The end of the timeline, representing by the highest revision number,
69 represents the "current" anticipated schema for the application.
70 Because the patch sequence can be calculated from any arbitrary
72 starting version, by keeping the historical set of changes in your
73 application as schema patches it is possible for the user of any older
74 application version to install the most current version of an
75 application and have their database upgraded smoothly and safely.
76 The recommended location to store the migration timeline is a shared
78 files directory, locatable using one of the functions from
79 File::ShareDir.
80 The timeline for your application can be specified in two different
82 forms, with different advantages and disadvantages.
83 Timeline Directories
85 A Timeline Directory is a directory on the filesystem containing a set
86 of Perl scripts named in a consistent pattern.
87 These patch scripts are named in the form migrate-$version.pl, where
89 $version is the schema version to migrate to. A typical timeline
90 directory will look something like the following.
91 migrate-01.pl
93 migrate-02.pl
94 migrate-03.pl
95 migrate-04.pl
96 migrate-05.pl
97 migrate-06.pl
98 migrate-07.pl
99 migrate-08.pl
100 migrate-09.pl
101 migrate-10.pl
102 ORLite::Migrate formulates a migration plan that starts at the current
104 database "user_version" pragma value, executing the migration script
105 that has the version "user_version + 1", then executing "user_version +
106 2" and so on.
107 It will continue stepping forwards until it runs out of patches to
109 execute.
110 The main advantage of a timeline directory is that each patch is run in
112 its own process and interpreter. Hundreds of patches can be produced by
113 many different authors, with certainty that the changes described in
114 each will be executed as intended.
115 The main disadvantage of using a timeline directory is that your
117 application must be able to identify the Perl interpreter it is run in
118 so that it can execute a sub-process. This may be difficult or
119 impossible for cases such as PAR-packaged applications and Perl
120 interpreters embedded inside .exe wrappers or larger non-Perl
121 applications.
122 In general, it is recommended that you use the timeline directory
124 approach unless you encounter a situation in which sub-process
125 execution (or locating the patch files) is difficult.
126 Timeline Classes
128 A timeline class places all of the schema patches into a single Perl
129 module, with each patch represented as a method name.
130 The following is an example of a trivial timeline class.
132 package t::lib::MyTimeline;
134 use strict;
136 use base 'ORLite::Migrate::Timeline';
137 my $UPGRADE1 = <<'END_SQL';
139 create table foo (
141 id integer not null primary key,
142 name varchar(32) not null
143 );
144 insert into foo values ( 1, 'foo' )
146 END_SQL
148 sub upgrade1 {
150 my $self = shift;
151 foreach ( split /;\s+/, $UPGRADE1 ) {
152 $self->do($_);
153 }
154 return 1;
155 }
156 sub upgrade2 {
158 $_[0]->do("insert into foo values ( 2, 'bar' )");
159 }
160 sub upgrade3 {
162 $_[0]->do("insert into foo values ( 3, 'baz' )");
163 }
164 1;
166 As with the patch files, the current state of the "user_version" pragma
168 will be examined, and each "upgradeN" method will be called to advance
169 the schema forwards.
170 The main advantage of a timeline class is that you will not need to
172 execute sub-processes, and so a timeline class will continue to
173 function even in unusual or exotic process contents such as PAR
174 packaging or .exe wrappers.
175 The main disadvantage of a timeline class is that the entire timeline
177 code must be loaded into memory no matter how many patch steps are
178 needed (and stay in memory after the migration has completed), and all
179 patches share a common interpreter and thus can potentially pollute or
180 corrupt each other.
181
183 Bugs should be reported via the CPAN bug tracker at
184 <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=ORLite-Migrate>
186 For other issues, contact the author.
188
190 Adam Kennedy <adamk@cpan.org>
191
193 Copyright 2009 - 2012 Adam Kennedy.
194 This program is free software; you can redistribute it and/or modify it
196 under the same terms as Perl itself.
197 The full text of the license can be found in the LICENSE file included
199 with this module.
200perl v5.32.0 2020-07-28 ORLite::Migrate(3)