Maypole::Manual::WorkfUser3Contributed Perl DocumeMaypole::Manual::Workflow(3)NAMEMaypole::Manual::Workflow - Maypole's Request Workflow
DESCRIPTION
This chapter describes the progress of a request through Maypole.
An application based on "Maypole" provides an Apache or CGI handler,
and eventually delivers a page. This document explains how that
happens, and how to influence it. We'll use the "BeerDB" project as our
example. Here's a diagram that gives an overview:
config $h
|
Maypole $r
Apache::Request |
+---- $r->get_request ---+
$ar |
|
$r->parse_location
|
$r->is_applicable
|
BeerDB::Beer $r->call_authenticate
->authenticate ------------+------------ $r->authenticate
|
$r->additional_data
|
$r->model_class->process($r)
|
$r->view_object->process($r)
Initialize class
When the first request comes in, the application class will call its
own "init" method, inherited from Maypole. This creates a new view
object.
Construction
Once we have initialized, the handler obtains the configuration for
your class, and puts it into a new object. We'll call this a request
object for the purposes of this document; it will be a new "BeerDB"
object.
Getting the request
Next, the handler calls "get_request" on the new object to have it
store a copy of the "Apache::Request". Of course, if you're not using
Apache, you might want to subclass this method to return something that
looks like an "Apache::Request" object, and possibly also subclass the
next stage too to get more control over what methods are called on your
"A::R"-lookalike. "get_request" is expected to put the object in the
"ar" slot of the request object.
Handling the URL
Typically, the details of the request will be passed in the URL. This
is done with the "parse_location" method, which is expected to populate
several slots of the request object. First, "table" and "action" should
be populated with the name of the table and the action parts of the
URL. Any other arguments should be placed in a listref in the "args"
slot, and GET and POST parameters should be arranged into a hash and
placed in the "query" and "params" slots, respectively.
Some people may not like the idea of passing everything around in the
URL; this is the method to override for you. Of course, you'll also
need to provide your own default templates to construct links using
your preferred format.
Is this an applicable URL?
Next, the "is_applicable" method works out if this is actually
something that "Maypole" should care about - whether the class exists
in the application, whether it supports the given action, and so on.
The action is "supported" if it exists in the model class (or its
ancestors) and is marked with the ":Exported" attribute; this stops web
users from firing off random subroutines in your code.
This should return an Apache status code; "OK" if the request should
proceed, "DECLINED" if it should be passed on to the default handlers,
or whatever other codes for permissions problems.
Are we allowed to do this?
We then look for an appropriate "authenticate" method to call; first it
will try calling the "authenticate" method of the model class, or, if
that does not exist, the "authenticate" method on itself. By default,
this allows access to everyone for everything. Your "authenticate"
methods must return an Apache status code: "OK" or "DECLINED". These
codes are defined by the Maypole::Constants module, which is
automatically used by your application.
Add any additional data to the request
You can write an "additional_data" method to do any additional fiddling
with the request object before it is despatched. Specifically, it
allows you to add to the "template_args" slot, which is a hash of
arguments to be added to the template, like this:
sub additional_data {
my $self = shift;
$self->{template_args}{answer} = 42;
}
which adds a new template variable "answer" with the value 42.
Ask model for widget set
Asking the model class to "process" the current request allows it to do
any work it needs for the given command, and populate the "objects" and
"template" slots of the request.
The model's "process" method is usually a thin wrapper around the
action that we have selected. It sets the template name to the name of
the action, fills "objects" with an object of that class whose ID comes
from the URL arguments if there is one. For instance, "/beer/foo/12"
will do the moral equivalent of
$r->objects([ BeerDB::Beer->retrieve(12) ]);
Then it calls the right method: in this case, the "foo" method with the
request object. This method will usually do any actions which are
required, including modifying the list of objects to be passed to the
template, or the name of the template to be called.
Ask view to process template
Now the view class has its "process" method called. It finds the
appropriate templates and calls the Template Toolkit processor.
The template processor is handed the objects, the template name, and
various other bits and pieces, and tries to find the right template. It
does this by looking first for "/beer/foo": that is, a specific
template appropriate to the class. Next, it looks at "/custom/foo", a
local modification, before looking for "/factory/foo", one of the
default templates that came with "Maypole".
The view puts the template's output in the "$r->{output}" slot. The
application's "handler" method calls the "send_output" method to push
it to the web server.
Default template arguments
If you're looking for the list of variables that are passed to the
Template Toolkit template by default, you'll find it in the View
chapter.
Links
Contents, Next The Beer Database Revisited, Previous Standard Templates
and Actions
perl v5.14.1 2005-11-23 Maypole::Manual::Workflow(3)
