Clever Geek Handbook

Understanding Blocks in Ruby / Rails

I have used scaffolding to create a CRUD system for posts. In the controller, I see the following:

class PostsController < ApplicationController
  # GET /posts
  # GET /posts.json
  def index
    @posts = Post.all

    respond_to do |format|
      format.html # index.html.erb
      format.json { render json: @posts }
    end
  end

  • What is it respond_to

    and where does it come from? Since it uses an operator do

    , it is some kind of iterable list I guess. On each format

    in this list, it will execute methods html

    and json

    .

  • How does it work { render json: @posts }

    in relation to the method json

    ? Passing render json: @posts

    as a method argument? Whether render

    and json

    subject to each object? I have never seen colon notation used outside of symbols.

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2 answers


  • PostsController inherits methods from ApplicationController and ApplicationController inherits from ActionController :: Base . This is where it comes from responds_to

    . A topic worth paying attention to is "finding a method".
  • do ... end

    - one of the ways to record a block. { render json: @posts }

    is another way.
  • json: "foo"

    - a more modern alternative to writing :json => "foo"

  • format

    is an arbitrary variable that you prepare for use within a block. render

    is a method and a :json

    is a symbol. respond_to

    will respond to user requests that conform to the Rails format requirements.
  • And to understand the method there is also the following:

http://apidock.com/rails/ActionController/MimeResponds/InstanceMethods/respond_to



And if you want to look at the source (it's a bit thick), for example, in the method respond_with

Paul was talking about, that's in the Rails source here:

rails / actionpack / Library / action_controller / metal / mime_responds.rb

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First of all, respond_to

not modern stuff in Rails. But I will provide a link for an explanation anyway .

The more modern respond_with helper .



You might find this screencast useful.

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