trusty (3) Jifty::Manual::ObjectModel.3pm.gz
NAME
Jifty::Manual::ObjectModel -- An overview of the Jifty object model
OVERVIEW
Jifty applications are generally built in a similar way. There's no reason you need to use the model
we've built, but we find it a reasonably OK way to do things.
This document should serve as a roadmap to the Jifty class library, as well as an introduction to the way
Jifty applications are put together.
We start with the classes in your application and move on to the bits of Jifty itself.
If you create a brand new application, let's call it "MyWeblog", and create one model class called
"MyWeblog::Post", you'll end up with the following files and directories:
MyWeblog/
etc/
config.yml
lib/
MyWeblog/
Model/
Post.pm
Action/
bin/
jifty
web/
templates/
static/
t/
#some test files.
At least that's the scaffolding Jifty creates for you. Behind the scenes, Jifty is actually doing a lot
more. Rather than create a bunch of little "stub" classes and libraries for you, Jifty generates them on
the fly. It's always possible to actually create these libraries when you need to customize the default
behavior, but we work really hard to make sure you don't need to.
Right now, Jifty is automatically creating libraries, static web pages and web templates.
We're not 100% satisfied with how Jifty automatically creates web templates and static pages and are
working to redesign that.
The library you see when creating a Jifty app is:
MyWeblog::Model::Post
"MyWeblog::Model::Post" describes the schema and business logic of your post class. It uses two
namespaces, "MyWeblog::Model::Post::Schema" that has actual column definitions and
"MyWeblog::Model::Post" that contains the (optional) business logic, access control and so on.
That's it. But if you look carefully at "MyWeblog::Model::Post", you'll see the line:
use base qw/MyWeblog::Record/;
How can that possibly work? There is no "MyWeblog::Record" class in your application. And Jifty, while it
tries to be a comprehensive framework, draws the line somewhat short of including application-specific
base classes for every application you might possibly contrive.
The answer lies in Jifty::ClassLoader, a utility module Jifty uses to create the boring stuff for you
when you need it.
It'd certainly be possible for Jifty to create every class you might need as a file on disk when you
first create your application (and indeed we may decide to do so if enough people yell at us), but when
the stub classes we'd provide are just little shims that inherit from or call to the Jifty core, it
doesn't make much sense to create them before you need them. You could build a Jifty application without
these shims by having your model classes inherit directly from Jifty::Record, but then you'll run into
trouble the second you want to add application-specific code and have to go back and retrofit each and
every one of your classes to use your new base class. It's a little thing, but one that can save you a
bunch of pain and suffering later on.
"MyWeblog::Record" is the first autogenerated class you'll run into but probably not the last. A full
list of everything Jifty provides for your new application follows:
You get one each of the these:
MyWeblog::Record
This class is, as discussed above, a thin wrapper around Jifty::Record. You might choose to create
your own "MyWeblog::Record" if you want to build in custom access control by overriding
"current_user_can" in Jifty::Record or want to implement methods that every model class should have
access to.
MyWeblog::Collection
We haven't talked much about collections yet, but as their name implies, collections are bundles of
Jifty::Record objects that match some set of criteria. It's relatively uncommon that you'll want to
override this, but if you want the rope, it's here.
MyWeblog::Notification
"MyWeblog::Notification" is an app-specific implementation of the Jifty::Notification email driver.
You might want to override this class if you want to set an application-specific header or footer for
all outgoing email.
MyWeblog::Dispatcher
"MyWeblog::Dispatcher" is an application-specific "dispatcher" class that allows you to write code
that runs when a client makes a request to the server before Jifty runs actions or renders templates.
See Jifty::Dispatcher for more information about the dispatcher.
MyWeblog::CurrentUser
Most every web application that grows past a personal hack eventually starts to provide
personalization, require access control or otherwise want to know who's currently in the driver's
seat. The "current user" for an application is a first-class object in Jifty. To get user-based
authentication working out of the box, you'll have to override the default "MyWeblog::CurrentUser".
(Out of the box, it treats everyone as the same user.) We're working to generalize the authentication
system we've used in a few Jifty apps so far to the point where it feels "right" as a core Jifty
component, but we're not quite there just yet.
Most of what you'll need to override in "MyWeblog::CurrentUser" is the "_init" function, which needs
to load up an application-specific model class that represents one of your users into its
"user_object" accessor. To make all this work, you'll also need an application-specific
"MyWeblog::Action::Login" and likely also a passel of user-management code.
(And yes, this is the topic of a future generalization and a future tutorial. At that point, a bunch
of this documentation will be extracted to Jifty::CurrentUser.)
But wait! There's more! You also get one each of these for your default model class:
MyWeblog::Model::PostCollection
It's no fun having a weblog that only shows you one post at a time, is it? Jifty provides you with
default Jifty::Collection classes for every Jifty::Record subclass in your model. You get all the
standard "limit", "order_by", "columns", paging support and so-on out of the box, but sometimes when
you're going to be getting collections matching certain criteria often, it makes sense to actually
create your own subclass and start dropping methods in.
MyWeblog::Action::CreatePost, MyWeblog::Action::UpdatePost, MyWeblog::Action::DeletePost
One of Jifty's strengths is that it makes it easy to build applications by tying application-specific
controller functions to your model classes and intuiting what parameters they take by having a look
inside the models.
For each class in your model, Jifty creates three actions, "Create","Update" and "Delete". They're
named, perhaps a bit unadventureously, "MyWeblog::Action::CreatePost",
"MyWeblog::Action::UpdatePost", "MyWeblog::Action::DeletePost" and inherit directly from
Jifty::Action::Record::Create, Jifty::Action::Record::Update and Jifty::Action::Record::Delete,
respectively. Sometimes, it makes sense to override these default actions when you want to change the
behaviour of one or more of the actions. One common use is to add or remove AJAX validation or
autocompletion for an argument or to change an argument's default value for webforms. This, isn't,
however the place to start inserting business logic or access control. That belongs in your model
class, which these wrappers will hand things off to. By putting logic in your actions, you make your
model classes less useful and run into trouble when you want to start scripting your model outside a
web environment.
There's no reason you need to stick with these default "implementations" if they're not meeting your
needs. Just create your own classes and Jifty will use your real classes instead.