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1 | <?xml version="1.0" ?> |
| 2 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> |
| 3 | <html xmlns="http://www.w3.org/1999/xhtml"> |
| 4 | <head> |
| 5 | <title>DBIx::Class::ResultSource::MultipleTableInheritance -- Use multiple tables to define your classes</title> |
| 6 | <meta http-equiv="content-type" content="text/html; charset=utf-8" /> |
| 7 | <link rev="made" href="mailto:amiri@akbuntu.nonet" /> |
| 8 | </head> |
| 9 | |
| 10 | <body style="background-color: white"> |
| 11 | |
| 12 | |
| 13 | <!-- INDEX BEGIN --> |
| 14 | <div name="index"> |
| 15 | <p><a name="__index__"></a></p> |
| 16 | |
| 17 | <ul> |
| 18 | |
| 19 | <li><a href="#name">NAME</a></li> |
| 20 | <li><a href="#synopsis">SYNOPSIS</a></li> |
| 21 | <li><a href="#why">WHY?</a></li> |
| 22 | <li><a href="#how">HOW?</a></li> |
| 23 | <li><a href="#author">AUTHOR</a></li> |
| 24 | <ul> |
| 25 | |
| 26 | <li><a href="#contributors">CONTRIBUTORS</a></li> |
| 27 | </ul> |
| 28 | |
| 29 | <li><a href="#license">LICENSE</a></li> |
| 30 | <li><a href="#see_also">SEE ALSO</a></li> |
| 31 | </ul> |
| 32 | |
| 33 | <hr name="index" /> |
| 34 | </div> |
| 35 | <!-- INDEX END --> |
| 36 | |
| 37 | <p> |
| 38 | </p> |
| 39 | <hr /> |
| 40 | <h1><a name="name">NAME</a></h1> |
| 41 | <p>DBIx::Class::ResultSource::MultipleTableInheritance -- Use multiple tables to define your classes</p> |
| 42 | <p> |
| 43 | </p> |
| 44 | <hr /> |
| 45 | <h1><a name="synopsis">SYNOPSIS</a></h1> |
| 46 | <pre> |
| 47 | { |
| 48 | package MyApp::Schema::Result::Coffee;</pre> |
| 49 | <pre> |
| 50 | __PACKAGE__->table_class('DBIx::Class::ResultSource::MultipleTableInheritance'); |
| 51 | __PACKAGE__->table('coffee'); |
| 52 | __PACKAGE__->add_columns( |
| 53 | "id", |
| 54 | { |
| 55 | data_type => "integer", |
| 56 | default_value => "nextval('coffee_seq'::regclass)", |
| 57 | is_auto_increment => 1, |
| 58 | is_foreign_key => 1, |
| 59 | is_nullable => 0, |
| 60 | size => 4, |
| 61 | }, |
| 62 | "flavor", |
| 63 | { |
| 64 | data_type => "text", |
| 65 | default_value => "good", |
| 66 | }, |
| 67 | );</pre> |
| 68 | <pre> |
| 69 | __PACKAGE__->set_primary_key("id");</pre> |
| 70 | <pre> |
| 71 | 1; |
| 72 | }</pre> |
| 73 | <pre> |
| 74 | { |
| 75 | package MyApp::Schema::Result::Sumatra;</pre> |
| 76 | <pre> |
| 77 | use parent 'Coffee';</pre> |
| 78 | <pre> |
| 79 | __PACKAGE__->table('sumatra');</pre> |
| 80 | <pre> |
| 81 | __PACKAGE__->add_columns( |
| 82 | "aroma", |
| 83 | { |
| 84 | data_type => "text", |
| 85 | default_value => undef, |
| 86 | is_nullable => 0, |
| 87 | }, |
| 88 | );</pre> |
| 89 | <pre> |
| 90 | 1; |
| 91 | } |
| 92 | |
| 93 | ...</pre> |
| 94 | <pre> |
| 95 | my $schema = MyApp::Schema->connect($dsn);</pre> |
| 96 | <pre> |
| 97 | my $cup = $schema->resultset('Sumatra')->new;</pre> |
| 98 | <pre> |
| 99 | print STDERR Dumper $cup->columns;</pre> |
| 100 | <pre> |
| 101 | $VAR1 = 'id'; |
| 102 | $VAR2 = 'flavor'; |
| 103 | $VAR3 = 'aroma';</pre> |
| 104 | <p>Inherit from this package and you can make a resultset class from a view, but that's more than a little bit misleading: the result is <strong>writable</strong> and updateable--transparently.</p> |
| 105 | <p>This is accomplished through the use of stored functions that map changes written to the view to changes to the underlying concrete tables.</p> |
| 106 | <p> |
| 107 | </p> |
| 108 | <hr /> |
| 109 | <h1><a name="why">WHY?</a></h1> |
| 110 | <p>In many applications, many classes are subclasses of others. Let's say you have this schema:</p> |
| 111 | <pre> |
| 112 | # Conceptual domain model |
| 113 | |
| 114 | class User { |
| 115 | has id, |
| 116 | has name, |
| 117 | has password |
| 118 | }</pre> |
| 119 | <pre> |
| 120 | class Investor { |
| 121 | has id, |
| 122 | has name, |
| 123 | has password, |
| 124 | has dollars |
| 125 | }</pre> |
| 126 | <p>That's redundant. Hold on a sec...</p> |
| 127 | <pre> |
| 128 | class User { |
| 129 | has id, |
| 130 | has name, |
| 131 | has password |
| 132 | }</pre> |
| 133 | <pre> |
| 134 | class Investor isa User { |
| 135 | has dollars |
| 136 | }</pre> |
| 137 | <p>Good idea, but how to put this into code?</p> |
| 138 | <p>One far-too common and absolutely horrendous solution is to have a "checkbox" in your database: a nullable "investor" column, which entails a nullable "dollars" column, in the user table.</p> |
| 139 | <pre> |
| 140 | create table "user" ( |
| 141 | "id" integer not null primary key autoincrement, |
| 142 | "name" text not null, |
| 143 | "password" text not null, |
| 144 | "investor" tinyint(1), |
| 145 | "dollars" integer |
| 146 | );</pre> |
| 147 | <p>Let's not discuss that further.</p> |
| 148 | <p>A second, better, solution is to break out the two tables into user and investor:</p> |
| 149 | <pre> |
| 150 | create table "user" ( |
| 151 | "id" integer not null primary key autoincrement, |
| 152 | "name" text not null, |
| 153 | "password" text not null |
| 154 | ); |
| 155 | |
| 156 | create table "investor" ( |
| 157 | "id" integer not null references user("id"), |
| 158 | "dollars" integer |
| 159 | );</pre> |
| 160 | <p>So that investor's PK is just an FK to the user. We can clearly see the class hierarchy here, in which investor is a subclass of user. In DBIx::Class applications, this second strategy looks like:</p> |
| 161 | <pre> |
| 162 | |
| 163 | my $user_rs = $schema->resultset('User'); |
| 164 | my $new_user = $user_rs->create( |
| 165 | name => $args->{name}, |
| 166 | password => $args->{password}, |
| 167 | );</pre> |
| 168 | <pre> |
| 169 | ...</pre> |
| 170 | <pre> |
| 171 | my $new_investor = $schema->resultset('Investor')->create( |
| 172 | id => $new_user->id, |
| 173 | dollars => $args->{dollars}, |
| 174 | );</pre> |
| 175 | <p>One can cope well with the second strategy, and it seems to be the most popular smart choice.</p> |
| 176 | <p> |
| 177 | </p> |
| 178 | <hr /> |
| 179 | <h1><a name="how">HOW?</a></h1> |
| 180 | <p>There is a third strategy implemented here. Make the database do more of the work. It'll save us some typing and it'll make for more expressive code. What if we could do this:</p> |
| 181 | <pre> |
| 182 | my $new_investor = $schema->resultset('Investor')->create( |
| 183 | name => $args->{name}, |
| 184 | password => $args->{password}, |
| 185 | dollars => $args->{dollars}, |
| 186 | ); |
| 187 | |
| 188 | And have it Just Work? The user ( {name => $args->{name}, password => $args->{password} } ) should be created transparently, and the use of either user or investor in your code should require no special handling. Deleting and updating $new_investor should also delete or update the user row.</pre> |
| 189 | <p>It does. User and investor are both views, their concrete tables abstracted away behind a set of rules and triggers. You would expect the above DBIC create statement to look like this in SQL:</p> |
| 190 | <pre> |
| 191 | INSERT INTO investor ("name","password","dollars") VALUES (...);</pre> |
| 192 | <p>But using MTI, it is really this:</p> |
| 193 | <pre> |
| 194 | INSERT INTO _user_table ("username","password") VALUES (...); |
| 195 | INSERT INTO _investor_table ("id","dollars") VALUES (currval('_user_table_id_seq',...) );</pre> |
| 196 | <p>For deletes, the triggers fire in reverse, to preserve referential integrity (foreign key constraints). For instance:</p> |
| 197 | <pre> |
| 198 | my $investor = $schema->resultset('Investor')->find({id => $args->{id}}); |
| 199 | $investor->delete;</pre> |
| 200 | <p>Becomes:</p> |
| 201 | <pre> |
| 202 | DELETE FROM _investor_table WHERE ("id" = ?); |
| 203 | DELETE FROM _user_table WHERE ("id" = ?);</pre> |
| 204 | <p></p> |
| 205 | <p> |
| 206 | </p> |
| 207 | <hr /> |
| 208 | <h1><a name="author">AUTHOR</a></h1> |
| 209 | <p>Matt S. Trout, <<a href="mailto:mst@shadowcatsystems.co.uk">mst@shadowcatsystems.co.uk</a>></p> |
| 210 | <p> |
| 211 | </p> |
| 212 | <h2><a name="contributors">CONTRIBUTORS</a></h2> |
| 213 | <p>Docs: Amiri Barksdale, <<a href="mailto:amiri@metalabel.com">amiri@metalabel.com</a>></p> |
| 214 | <p> |
| 215 | </p> |
| 216 | <hr /> |
| 217 | <h1><a name="license">LICENSE</a></h1> |
| 218 | <p>This library is free software; you can redistribute it and/or modify |
| 219 | it under the same terms as Perl itself.</p> |
| 220 | <p> |
| 221 | </p> |
| 222 | <hr /> |
| 223 | <h1><a name="see_also">SEE ALSO</a></h1> |
| 224 | <p><a href="/DBIx/Class.html">the DBIx::Class manpage</a> |
| 225 | <a href="/DBIx/Class/ResultSource.html">the DBIx::Class::ResultSource manpage</a></p> |
| 226 | |
| 227 | </body> |
| 228 | |
| 229 | </html> |
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