Rails 5 - Understanding the new action and rendering errors - ruby-on-rails

Question

My questions is regarding section 5.10 of the official Rails guide
I have an articles model with fields Title and Text
article.rb :
class Article < ApplicationRecord
validates :title, presence: true, length: { minimum: 5 }
end
articles_controller.rb :
class ArticlesController < ApplicationController
def index
#articles = Article.all
end
def show
#article = Article.find(params[:id])
end
def new
#article = Article.new
end
def create
#article = Article.new(article_params)
if #article.save
redirect_to #article
else
render 'new'
end
end
private
def article_params
params.require(:article).permit(:title, :text)
end
end
The guide says that
#article = Article.new
needs to be added to the new action otherwise otherwise #article would be nil in our view, and calling #article.errors.any? would throw an error. Here is the new.html.erb :
<%= form_with scope: :article, url: articles_path, local: true do |form| %>
<% if #article.errors.any? %>
<div id="error_explanation">
<h2>
<%= pluralize(#article.errors.count, "error") %> prohibited
this article from being saved:
</h2>
<ul>
<% #article.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<p>
<%= form.label :title %><br>
<%= form.text_field :title %>
</p>
<p>
<%= form.label :text %><br>
<%= form.text_area :text %>
</p>
<p>
<%= form.submit %>
</p>
<% end %>
<%= link_to 'Back', articles_path %>
What I am able to understand is when there is an error, it is present in #articles so #article.errors.any? helps in showing the errors when the 'new' view is rendered. It indeed works as expected but what I am not able to understand is #article = Article.new in the new action should reset the #article and the errors should be lost after the user is redirected to new. But somehow, the errors are not lost and are indeed being displayed. How is this happening ?

Answer 1

Both render and redirect are different things.
render Renders the content that will be returned to the browser as the response body.
redirect or redirect_to - Redirect is concerned about telling the browser it needs to make a new request to a different location or to the same location as given in path.
It is clearly mentioned in artcle 5.10
Notice that inside the create action we use render instead of redirect_to when save returns false. The render method is used so that the #article object is passed back to the new template when it is rendered. This rendering is done within the same request as the form submission, whereas the redirect_to will tell the browser to issue another request.
Note: You can read render vs redirect in detail
As per your question
def new
#article = Article.new
end
def create
#article = Article.new(article_params)
if #article.save
redirect_to #article
else
render 'new' # this will add error (validations)
end
end
def create
#article = Article.new(article_params)
if #article.save
redirect_to #article
else
redirect_to 'new' # this will not add any error as this is new request and #article will initialise again.
new #same as redirect
end
end
Edit: Creating Form Objects with ActiveModel. A form object is an object designed specifically to be passed to form_for
We always check for errors #article.errors.any? it will execute if #article object contains any error messages
Please read form_for doc.

Answer 2

render doesn't run any code in the new method, it just uses the new.html.x view. As such, #article = Article.new is never executed.
If you wanted the code from new run, you would need to actually call that method:
def create
#article = Article.new(article_params)
if #article.save
redirect_to #article
else
new #actually runs the code in the 'new' method
render 'new' # doesn't go anywhere near the new method, just uses its view
end
end