1Maypole::Manual::WorkflUoswe(r3)Contributed Perl DocumenMtaaytpioolne::Manual::Workflow(3)
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6 Maypole::Manual::Workflow - Maypole's Request Workflow
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9 This chapter describes the progress of a request through Maypole.
10 An application based on "Maypole" provides an Apache or CGI handler,
12 and eventually delivers a page. This document explains how that
13 happens, and how to influence it. We'll use the "BeerDB" project as our
14 example. Here's a diagram that gives an overview:
15 config $h
17 |
18 Maypole $r
19 Apache::Request |
20 +---- $r->get_request ---+
21 $ar |
22 |
23 $r->parse_location
24 |
25 $r->is_applicable
26 |
27 BeerDB::Beer $r->call_authenticate
28 ->authenticate ------------+------------ $r->authenticate
29 |
30 $r->additional_data
31 |
32 $r->model_class->process($r)
33 |
34 $r->view_object->process($r)
35 Initialize class
37 When the first request comes in, the application class will call its
38 own "init" method, inherited from Maypole. This creates a new view
39 object.
40 Construction
42 Once we have initialized, the handler obtains the configuration for
43 your class, and puts it into a new object. We'll call this a request
44 object for the purposes of this document; it will be a new "BeerDB"
45 object.
46 Getting the request
48 Next, the handler calls "get_request" on the new object to have it
49 store a copy of the "Apache::Request". Of course, if you're not using
50 Apache, you might want to subclass this method to return something that
51 looks like an "Apache::Request" object, and possibly also subclass the
52 next stage too to get more control over what methods are called on your
53 "A::R"-lookalike. "get_request" is expected to put the object in the
54 "ar" slot of the request object.
55 Handling the URL
57 Typically, the details of the request will be passed in the URL. This
58 is done with the "parse_location" method, which is expected to populate
59 several slots of the request object. First, "table" and "action" should
60 be populated with the name of the table and the action parts of the
61 URL. Any other arguments should be placed in a listref in the "args"
62 slot, and GET and POST parameters should be arranged into a hash and
63 placed in the "query" and "params" slots, respectively.
64 Some people may not like the idea of passing everything around in the
66 URL; this is the method to override for you. Of course, you'll also
67 need to provide your own default templates to construct links using
68 your preferred format.
69 Is this an applicable URL?
71 Next, the "is_applicable" method works out if this is actually
72 something that "Maypole" should care about - whether the class exists
73 in the application, whether it supports the given action, and so on.
74 The action is "supported" if it exists in the model class (or its
75 ancestors) and is marked with the ":Exported" attribute; this stops web
76 users from firing off random subroutines in your code.
77 This should return an Apache status code; "OK" if the request should
79 proceed, "DECLINED" if it should be passed on to the default handlers,
80 or whatever other codes for permissions problems.
81 Are we allowed to do this?
83 We then look for an appropriate "authenticate" method to call; first it
84 will try calling the "authenticate" method of the model class, or, if
85 that does not exist, the "authenticate" method on itself. By default,
86 this allows access to everyone for everything. Your "authenticate"
87 methods must return an Apache status code: "OK" or "DECLINED". These
88 codes are defined by the Maypole::Constants module, which is
89 automatically used by your application.
90 Add any additional data to the request
92 You can write an "additional_data" method to do any additional fiddling
93 with the request object before it is despatched. Specifically, it
94 allows you to add to the "template_args" slot, which is a hash of
95 arguments to be added to the template, like this:
96 sub additional_data {
98 my $self = shift;
99 $self->{template_args}{answer} = 42;
100 }
101 which adds a new template variable "answer" with the value 42.
103 Ask model for widget set
105 Asking the model class to "process" the current request allows it to do
106 any work it needs for the given command, and populate the "objects" and
107 "template" slots of the request.
108 The model's "process" method is usually a thin wrapper around the
110 action that we have selected. It sets the template name to the name of
111 the action, fills "objects" with an object of that class whose ID comes
112 from the URL arguments if there is one. For instance, "/beer/foo/12"
113 will do the moral equivalent of
114 $r->objects([ BeerDB::Beer->retrieve(12) ]);
116 Then it calls the right method: in this case, the "foo" method with the
118 request object. This method will usually do any actions which are
119 required, including modifying the list of objects to be passed to the
120 template, or the name of the template to be called.
121 Ask view to process template
123 Now the view class has its "process" method called. It finds the
124 appropriate templates and calls the Template Toolkit processor.
125 The template processor is handed the objects, the template name, and
127 various other bits and pieces, and tries to find the right template. It
128 does this by looking first for "/beer/foo": that is, a specific
129 template appropriate to the class. Next, it looks at "/custom/foo", a
130 local modification, before looking for "/factory/foo", one of the
131 default templates that came with "Maypole".
132 The view puts the template's output in the "$r->{output}" slot. The
134 application's "handler" method calls the "send_output" method to push
135 it to the web server.
136 Default template arguments
138 If you're looking for the list of variables that are passed to the
139 Template Toolkit template by default, you'll find it in the View
140 chapter.
141 Links
143 Contents, Next The Beer Database Revisited, Previous Standard Templates
144 and Actions
145perl v5.38.0 2023-07-20 Maypole::Manual::Workflow(3)