Datasheet

Chapter 1: Building Resources

When the respond_to method is called, the outer block is invoked. Each format method is called, and

does nothing unless the format method name matches the type of the request. (Metaprogramming fans

should note that this is elegantly implemented using

method_missing .) If the types match, then

behavior associated with that type is invoked — either the block if one is explicitly passed or the default

behavior if not.

The convention is to have nothing in your respond_to block except for the format calls, and nothing in

the format calling blocks except the actual rendering call being made. This goes along with the general

idea in Rails design that the controller should be as thin as possible, and that complex data processing

should be handled in the model object.

The

respond_to method adds a lot of flexibility to your Rails controller — adding XML data serialization

or RSS feeds is nearly trivial. The syntax, I think, may still have some tweaking ahead of it — I ’ m not sure

there ’ s a lot of love for the way default behaviors are specified, and if the rendering is complex, the nested

blocks can become hard to read.

Rails defines eight formats for you:

atom , html , ics , js , rss , text , xml , and yaml . Just to be clear on

this,

html is used for ordinary browser output, atom and rss should be used for feeds, xml and yaml

are used for object syndication,

ics is the standard iCalendar format for calendar data, text is often

used for simple serialization, and

js is used either to serialize data via the JSON format or as the target

of an Ajax call that would trigger JavaScript.

Adding your own formats is simple, assuming that the format has a MIME type. Suppose you wanted to

allow a URL like

/recipes.png to return some kind of graphical display of your recipe list. All you

need to do is go into the

config/environment.rb file and add the following line:

Mime::Type.register “image.png”, :png

Now any respond_to block in your application will enable you to use format.png as a method.

Show

The default show method is nearly identical to the index method, except that it only takes a single recipe

from the database, and renders the

show.html.erb file.

# GET /recipes/1

# GET /recipes/1.xml

def show

@recipe = Recipe.find(params[:id])

respond_to do |format|

format.html # show.html.erb

format.xml { render :xml = > @recipe }

end

The render :xml = > @recipe method call creates an XML representation of the data object by making

all of the attributes of the data object into subordinate tags of the XML (see Chapter 9 for more details).

c01.indd 12c01.indd 12 1/30/08 4:02:24 PM1/30/08 4:02:24 PM