1Maypole::Manual::Model(U3s)er Contributed Perl DocumentatMiaoynpole::Manual::Model(3)
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6 Maypole::Manual::Model - Maypole Model Classes
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9 Maypole's model classes provide an interface to your data store. In
10 principle Maypole can connect to pretty much any data source, but the
11 default model is based on the popular Class::DBI object interface that
12 uses the near-universal DBI Perl interface to databases.
13 Maypole::Model::CDBI
15 Maypole model classes are pretty evil. The very first thing a Maypole
16 model class will do in a Maypole application is to cause a load of
17 table-based classes to come into being, and then assimilate them.
18 What I mean by this is that when you set up a Maypole application, in
20 your driver class, you'll say something like this:
21 BeerDB->setup("dbi:mysql:beerdb");
23 "setup" is a Maypole method, and it hands its parameter to the model
25 class. In our case, the argument is a DBI connect string, because
26 that's what "Maypole::Model::CDBI", the "Class::DBI"-based model
27 expects. "Maypole::Model::CDBI" has a method called "setup_database"
28 that creates all the "Class::DBI" table classes after connecting to the
29 database with that connect string. It does this by using
30 "Class::DBI::Loader", a utility module which asks a database about its
31 schema and sets up classes such as "BeerDB::Beer" to inherit from
32 "Class::DBI".
33 Now it gets interesting. The names of these classes are stashed away in
35 the application's configuration, and then Maypole forcibly has these
36 classes inherit from the model class. Our "BeerDB::Beer" now inherits
37 both from "Class::DBI" and "Maypole::Model::CDBI".
38 This is useful for two reasons. The first reason is that
40 "Maypole::Model::CDBI" is stuffed full of "Class::DBI" goodies that
41 make writing Maypole applications a lot easier:
42 package Maypole::Model::CDBI;
44 use base qw(Maypole::Model::Base Class::DBI);
45 use Maypole::Model::CDBI::AsForm;
46 use Class::DBI::FromCGI; # probabyly broken .
47 use Class::DBI::Loader;
48 use Class::DBI::AbstractSearch;
49 use Class::DBI::Plugin::RetrieveAll;
50 use Class::DBI::Pager;
51 We'll meet most of these goodies in the Standard Templates and Actions
53 chapter, where we explain how "Maypole::Model::CDBI" works.
54 The second reason why we want our table classes to inherit from
56 "Maypole::Model::CDBI" is because it provides a useful set of default
57 actions. So what's an action, and why are they useful?
58 Maypole::Model::CDBI::Plain
60 The 'Plain' maypole Model : "Maypole::Model::CDBI" allows you
61 package Foo;
63 use 'Maypole::Application';
64 Foo->config->model("Maypole::Model::CDBI::Plain");
66 Foo->setup([qw/ Foo::SomeTable Foo::Other::Table /]);
67 # untaint columns and provide custom actions for each class
69 Foo::SomeTable->untaint_columns(email => ['email'], printable => [qw/name description/]);
71 Foo::Other::Table->untaint_columns ( ... );
73 sub Foo::SomeTable::SomeAction : Exported {
75 . . .
77 }
79 Extending a model class with actions
81 Maypole operates primarily by turning URLs into method calls on a model
82 class. All that the model stage of Maypole's operation does, when it
83 comes down to it, is maintain a mapping of tables to classes, and
84 despatch a HTTP request to a method call on the relevant table class.
85 This means that if you request a URL such as
86 http://localhost/beerdb/brewery/delete/20
88 Maypole's first stage of operation is to turn that into
90 "BeerDB::Brewery->delete(20)". Now, it's slightly more complex than
91 that. Firstly because it doesn't actually pass the parameter 20, but it
92 passes an object representing row 20 in the database, but we can gloss
93 over that for the second. No, the real issue is that Maypole does not
94 allow you to call just any method in the table class; that would be
95 somewhat insecure.
96 Instead, Maypole makes a distinction between the kind of methods that
98 only the class itself and other Perl code can call, and the kind of
99 methods that anyone can call from a URL. This latter set of methods are
100 called exported methods, and exporting is done by means of Perl
101 attributes. You define a method to be exported like so:
102 sub drink :Exported {
104 This will allow the user to access "/beerdb/beer/drink" over the web.
106 An exported method accompanied with a template to render its output is
107 sometimes called an action.
108 Maypole model classes like "Maypole::Model::CDBI" come with a
110 relatively handy set of actions which are all you need to set up a CRUD
111 (Create, Read, Update, Delete) database front-end: viewing a row in a
112 database, editing it, adding a new one, deleting, and so on. The most
113 important thing about Maypole, though, is that it doesn't stop there.
114 You can add your own.
115 For instance, in our beer database application, we could create a
117 "BeerDB::Beer" package, and put some additional actions in there.
118 package BeerDB::Beer;
120 sub top_five :Exported {
121 my ($class, $r) = @_;
122 $r->objects([ ($r->retrieve_all_sorted_by("score"))[-5..-1] ]);
123 }
124 Our action is called as a class method with the Maypole request object.
126 It uses the "Class::DBI::Plugin::RetrieveAll" module's
127 "retrieve_all_sorted_by" mixin to get the top five scoring beers, and
128 puts these in the "objects" slot of the request of object. Next, the
129 view class will come along and process the "top_five" template with
130 these five beers.
131 We'll look more at how to put together actions in the Standard
133 Templates and Actions chapter and our case studies.
134 Links
136 Contents, Next Maypole View Classes, Previous Introduction to Maypole
137perl v5.28.1 2006-09-05 Maypole::Manual::Model(3)