4.1. Using the
Scaffold Method
We've already demonstrated a working model for
Photo Share, including photos, categories, slideshows, and slides,
and you should be able to manage schema from Active Record objects
with the Rails console. The next step is to use scaffolding to
build primitive web user interfaces for these classes. Scaffolding
will take you a good ways down the road, but it won't generate a
completed application. That's okay. We're looking for a head start,
not a completed production-quality application.
4.1.1. A List of
Photos
Let's start by letting the user manage a list of
photos from the Web. Ensure that you've got a database, that it's
configured, and that you've got tables with model objects for
slides, slideshows, categories, and photos. If your server is not
started, restart it as usual with ruby script/server.
Point your browser to http://localhost:3000/ to make sure
things are working. You'll see the Rails welcome page if everything
is working correctly. Let's build some scaffolding.
You'll start to build scaffolding using the
scaffold method. That method goes into the controller, so
we need to generate a controller called Photos:
ruby script/generate controller Photos
Add the scaffold :photo method to
photo_controller.rb, like this:
class PhotosController < ApplicationController
scaffold :photo
end
That's all you needRails will do the rest. Now,
load the URL http://localhost:3000/photos to
see the scaffolding in action. You'll see a list of photos, with
links to create new photos, edit existing photos, and show existing
photos. With the simple scaffold :photo statement, you got
all the pages that show in
"#rubyrails-chp-4-fig-1">Figure 4-1. The scaffolding generates
surprisingly complete controller and view code. To be sure, the
scaffolding does not generate production-ready code, but it's a
starting point. The next shows how scaffolding works.
|
If you get the following error when trying to
access the application:
Mysql::Error in Photo#list
Access denied for user: 'root@localhost' (Using password: NO)
it means that you forgot to restart the
server.
|
|
4.1.2. More
Metaprogramming
scaffold :photo does the magic.
scaffold is a method on
ActionController. :photo is a symbol that determines
the Active Record model that Rails uses for this scaffold. When you
specify this single method, Rails adds to your controller the nine
methods in "#rubyrails-chp-4-table-1">Table
4-1. Four of them render views. Together, the methods build a
simple CRUD interface for your Active Record model based on the
model object. Within the model, the @@content_columns
attribute contains information about each of the columns in the
database.
Table 4-1. The scaffold :target method on
a Rails controller creates the methods on the controller
|
Methods
|
Purpose
|
View
|
|
index
|
Renders a welcome page. By default,
index redirects to the list controller action.
Also, by default, when a user specifies a controller but no action,
Rails invokes the index action.
|
No
|
|
list
|
Renders a view with a paginated list of
target objects, in which the target object
is the model object for the scaffold.
|
Yes
|
|
create(target)
|
Creates and saves an Active Record object from
the target object.
|
No
|
|
new
|
Renders a view to create a new controller
object.
|
Yes
|
|
edit(id)
|
Renders a view to edit the target object with
the supplied id.
|
Yes
|
|
update(id)
|
Updates the active record target object with the
supplied id.
|
No
|
|
show(id)
|
Renders a view to show an object
|
Yes
|
|
destroy(id)
|
Destroys the object of type
target with the supplied
id.
|
No
|
|
render_scaffold
|
Renders the default view for the view methods if
no .rhtml view is present.
|
N/A
|
Most of the methods listed in Table 4-1 wind up calling the
render_scaffold method, which checks to see whether you've
added the corresponding view. (Remember that by default, Rails
views will have the same name as the controller method.) If so,
Rails uses your views. Otherwise, the controller provides default
views. |
]