Rails' respond_to - syntax analysis

Question

Here is a Rails code:

respond_to do |format|
  format.html
  format.xml { render :xml => @users }
  format.json { render :json => @users }
end

I know what it does. But I don't know the meaning of the commands syntax-wise.

format.xml -- what is xml, is this a method which an object format has, correct? Where do I find its signature (or description)?
{ } -- a block or a hash? I think this is a block.
render -- a method? where do I find its signature (where in api docs)?
:xml => @users -- a hash, where :xml => is a key, correct?

So it could be reprented as, right?:

respond_to do |format|
  format.html
  format.xml do
    render(:xml => @users)
  end 
  format.json do
    render(:json => @users)
  end
end

Have you checked out apidock.com ? http://apidock.com/rails/ActionController/MimeResponds/InstanceMethods/respond_to — scaryguy, Aug 10 '13 at 20:45
Possible duplicate: http://stackoverflow.com/questions/9492362/rails-how-does-the-respond-to-block-work — cmpolis, Aug 10 '13 at 20:58

score 0 · Answer 1 · answered Aug 10 '13 at 21:06

format comes from the request made to the method, http://app.com/controller/method.format where format could be .html or .csv etc. The meaning of format.xml is simply to check if the user requested an xml page (http://app.com/controller/method.xml.
Block, just like you describe.
At the apidock! http://apidock.com/rails/ActionController/Base/render
Correct, render will act depending on the key that exists. In your case, as the existing key is :xml the render method will output @users formatted as XML.

score 0 · Accepted Answer · answered Aug 10 '13 at 21:29

format.*

Using the debugger, I learnt that format is an instance of ActionController::MimeResponds::Collector. It includes AbstractController::Collector, which uses method_missing to respond to various format calls.

if Mime::SET.include?(mime_constant)
  AbstractController::Collector.generate_method_for_mime(mime_constant)
  send(symbol, &block)
else
  # ...

{ render xml: ... }

Looking at method_missing, it's clear that it expects a block.

render

Yes, render is a method. Documentation.

:xml => @user

Yes, it's a hash. The key is the symbol :xml. It can also be written as

render xml: @user

render(xml: @user)

render({xml: @user})
render({:xml => @user})

Rails' respond_to - syntax analysis

2 Answers2

format.*

{ render xml: ... }

render

:xml => @user