Rails: How to pass instance variables from a controller to render partial - ruby-on-rails

Question

I am having trouble passing an instance variable (#article) from a controller (articles_controller.rb) to a partial render (_form.html.erb) in Ruby.
Here is the error from being sent back:
`undefined method `errors' for nil:NilClass`
articles_controller.rb:
class ArticlesController < ApplicationController
def new
end
def create
#article = Article.new(article_params)
if #article.save
redirect_to #article
else
render 'new'
end
end
def update
#article = Article.find(params[:id])
if #article.update(article_params)
redirect_to #article
else
render 'edit', :article => #article
end
end
def show
#article = Article.find(params[:id])
end
def index
#articles = Article.all
end
private
def article_params
params.require(:article).permit(:title, :text)
end
end
new.html.erb
<h1>New Article</h1>
<%= form_for :article, url: articles_path do |f|%>
<%= render partial: "form", :locals => {:article => #article} %>
<% end %>
<% link_to 'Back', articles_path %>
_form.html.erb
<% 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_messeages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<p>
<%= f.label :title %><br />
<%= f.text_field :title %>
</p>
<p>
<%= f.label :text %><br />
<%= f.text_area :text %>
</p>
<p>
<%= f.submit %>
</p>
Any help would be appreciated

Answer 1

def new
#article = Article.new
end
<%= render partial: "form", collection: #article %>
or even
<%= form_for #article do |f|%>
<%= render 'form' %>
<% end %>
depends on your needs

Answer 2

I had this challenge when working on a Rails 6 application.
I wanted to use an instance variable in a partial (app/views/shared/_header.html.erb) that was defined in a different controller (app/controllers/categories_controller.rb).
Here's how I did it:
The instance variable that I wanted to use is #categories which is defined as:
# app/controllers/categories_controller.rb
class CategoriesController < ApplicationController
def index
#categories = Category.all
end
.
.
.
end
Firstly, I rendered the app/views/shared/_header.html.erb partial in the app/views/layouts/application.html.erb and passed the #categories instance variable into it this way:
<%= render partial: '/shared/header', locals: { categories: #categories } %>
And then I used the instance variable in the partial this way:
# app/views/shared/_header.html.erb
<% #categories.each do |category| %>
<%= link_to category do %>
<%= category.name %>
<% end %>
<% end %>
However, this will require a controller action that sets a #categories instance variable for every controller views that will use the partial.
If you want to make variables globally available in your controllers and views, this could help: Rails: Set a common or global instance variable across several controller actions
That's all.
I hope this helps

Answer 3

You should do like this, removing #. You are passing it to local variable article so you could access it with article not #article:
<% 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_messeages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<p>
<%= f.label :title %><br />
<%= f.text_field :title %>
</p>
<p>
<%= f.label :text %><br />
<%= f.text_area :text %>
</p>
<p>
<%= f.submit %>
</p>
For more info, please take a look at passing-local-variables