instance variable vs. symbol in ruby on rails (form_for)

Question

hi, i'm new to ruby on rails and am working with version 2.3 on mac osx. i am trying to create the same functionality a scaffold creates, but on my own. i created a "post" controller, view, and model. in post controller, i have the following:

class PostController < ApplicationController
  def index
  end

  def new
    @post = Post.new
  end
end

in new.html.erb, i have the following:

<h1>New Post</h1>

<% form_for :post do |f| %>

    <%= f.text_field :title %>

<% end %>

i noticed that in the scaffold generated code, the use the instance variable @post for the form_for helper. why do they use the instance variable in the scaffold generated form if passing the symbol :post in form_for does the exact same thing, while a symbol requires changing the config of the routes?

thank you very much, yuval

Answer 1

One possible reason is that it makes the code for the form to create a new post more similar to the code for a form to update an existing post.

Answer 2

if you use symbol :post it creates

<form action="/posts" method="post">

if you use the instance @post

for @post = Post.new you will get

<form action="/posts/create" class="new_account" id="new_account" method="post">

for @post = Post.find(1) you will get

<form action="/posts/update" class="edit_account" id="edit_account_1" method="post">
<input name="_method" type="hidden" value="put">

if you have different forms for your new and your edit no big deal but more likey than not your new and your edit forms are going to be identical or close to it

so if you use the instance variable @post you can put all the form code into _form and just call the partial and it will handle the rest based on if you pass in a new record or an existing record