--- /dev/null
+=pod
+
+=head1 NAME
+
+Apache::MVC::Workflow - Describes the progress of a request through Apache::MVC
+
+=head1 SYNOPSIS
+
+ config $h
+ |
+ Apache::MVC $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)
+
+
+=head1 DESCRIPTION
+
+An application based on C<Apache::MVC> will provide an Apache handler,
+and eventually deliver a page. This document explains how that happens,
+and how to influence it. We'll use the C<BeerDB> project as our example.
+
+=head2 Initialize class
+
+When the first request comes in, the class will call its own
+C<init> method. This creates a new view object, sets up inheritance
+relationships between the model classes and their parent, and so on.
+
+=head2 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
+I<object> for the purposes of this document; it will be a new C<BeerDB>
+object.
+
+=head2 Getting the request
+
+Next, the handler calls C<get_request> on the new object to have it
+store a copy of the C<Apache::Request>. Of course, if you're not using
+Apache, you might want to subclass this method to return something that
+looks like an C<Apache::Request> object, and possibly also subclass the
+next stage too to get more control over what methods are called on your
+C<A::R>-lookalike. C<get_request> is expected to put the object in the
+C<ar> slot of the request object.
+
+=head2 Handling the URL
+
+Typically, the details of the request will be passed in the URL. This is
+done with the C<parse_location> method, which is expected to populate
+several slots of the request object. First, C<table> and C<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
+C<args> slot, and GET and POST parameters should be arranged into a hash
+and placed in the C<query> and C<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.
+
+=head2 Is this an applicable URL?
+
+Next, the C<is_applicable> method works out if this is actually
+something that C<Apache::MVC> 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 C<:Exported> attribute; this stops web
+users from firing off random subroutines in your code.
+
+This should return an Apache status code; C<OK> if the request should
+proceed, C<DECLINED> if it should be passed on to the default handlers,
+or whatever other codes for permissions problems.
+
+=head2 Are we allowed to do this?
+
+We then look for an appropriate C<authenticate> method to call; first
+it will try calling the C<authenticate> method of the model class, or,
+if that does not exist, the C<authenticate> method on itself. By
+default, this allows access to everyone for everything. Similarly, this
+should return an Apache status code.
+
+=head2 Add any additional data to the request
+
+The open-ended C<additional_data> method allows any additional fiddling
+with the request object before it is despatched. Specifically, it allows
+you to add to the C<template_args> slot, which is a hash of arguments to
+be added to the template.
+
+=head2 Ask model for widget set
+
+Asking the model class to C<process> the current request allows it to do
+any work it needs for the given command, and populate the C<objects> and
+C<template> slots of the request.
+
+=head2 Ask view to process template
+
+Now the view class has its C<process> method called, finds the
+appropriate templates, passes the C<objects> and any additional data to
+the template, and pushes the output to the web server.
+
+We will go into more detail about these last two phases.
+
+=head1 Model class processing
+
+The model's C<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 C<objects> with an object of that class whose ID comes
+from the URL arguments if there is one. For instance, C</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 C<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.
+
+=head1 Template class processing
+
+Finally, 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 C</beer/foo>: that is, a
+specific template appropriate to the class. Next, it looks at
+C</custom/foo>, a local modification, before looking for
+C</factory/foo>, one of the default templates that came with
+C<Apache::MVC>.
+
+=head2 Default template arguments
+
+The following things are passed to the Template Toolkit template by
+default:
+
+=over 3
+
+=item request
+
+The whole C<Apache::MVC> request object, for people getting really dirty
+with the templates.
+
+=item objects
+
+The objects handed to us by the model.
+
+=item base
+
+The base URL of the application.
+
+=item config
+
+The whole configuration hash for the application.
+
+=item classmetadata
+
+A hash consisting of:
+
+C<name> - The name of the model class for the request: e.g. C<BeerDB::Beer>.
+
+C<columns> - The names of the columns in this class.
+
+C<colnames> - A hash mapping between the database's idea of a column
+name and a human-readable equivalent. (C<abv> should be mapped to
+C<A.B.V.>, perhaps.)
+
+C<related_accessors> - A list of accessors which are not exactly fields
+in the table but are related by a has-many relationship. For instance,
+breweries have many beers, so C<beers> would appear in the list.
+
+C<moniker> - The human-readable name for the class: C<beer>.
+
+C<plural> - The same, only plural: C<beers>.
+
+C<cgi> - A hash mapping columns and C<HTML::Element> objects
+representing a form field for editing that column.
+
+C<description> - (Perhaps) a user-supplied description of the class.
+
+=back
+
+Additionally, depending on the number of objects, there will be an alias
+for the C<objects> slot with the name of the moniker or plural moniker.
+
+That sounds a bit tricky, but what it means is that if you look at
+C</beer/view/4> then C<beer> will be populated with a C<BeerDB::Beer>
+object with ID 4. On the other hand, if you look at C</beer/list> you
+can get all the beers in C<beers> as well as in C<objects>.
+
+
projects / maypole.git / blobdiff