In this section of the Rails guide, it is instructed to add #article = Article.new in the new method of ArticlesController, explaining that otherwise we won't be able to access #article.errors.
From what I understand, #articles = Article.new creates a new instance of Article, and what we need is the #article variable that we tried to submit. I know it works but I need to understand why.
Controller code:
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
View code:
<%= 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 articles 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 %>
<% end %>
<%= link_to 'Back', articles_path %>
It says this:
The reason why we added #article = Article.new in the
ArticlesController is that otherwise #article would be nil in our
view, and calling #article.errors.any? would throw an error.
so it has nothing to do with accessing validation errors.
Without the #article variable in new action you would call errors method in your view on nil value and nil doesn't have such a method, so you would get an error undefined method 'errors' for nil:NilClass. In case of #article variable set to Article.new you call errors method on an Article class instance and since there are no validation errors (yet) the #error_explanation block will not be rendered.
But when you try to create a new record, then validation occurs. And if there are validation errors your rails app renders the new template again, but it does it with the create action. Therefore, the #article variable this time is the one from the create method and since we have validation errors in it, the #error_explanation block will be rendered and user will see what's wrong.
Related
I want to create a new article object, but have this error:
Showing
/Users/levanngoc/code/blog_app/app/views/articles/new.html.erb where
line #3 raised:
undefined method `errors' for nil:NilClass
How can I fix it?
this is my controller:
class ArticlesController < ApplicationController
def index
#article = Article.all
end
def show
#article = Article.find(params[:id])
end
def new
end
def edit
end
def create
#article = Article.new(article_params)
if #article.save
redirect_to #article
else
render 'new'
end
end
def update
end
def destroy
end
private
def article_params
params.require(:article).permit(:title, :text)
end
end
this is my view file: new.html.erb
<h1>New Article</h1>
<%= 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 %>
Your new view uses #article but the new action in the controller doesn't create this instance variable. You must change it to:
def new
#article = Article.new
end
You must declare:
#article = Article.new
I've been following the rails blog tutorial (you know, that one ) and i've come to a point where every time i reference #articles on the update form, rails takes it as a nil, it says:
First argument in form cannot contain nil or be empty
Here's the form
<h1>Edit article</h1>
<%= form_for #article do |f| %>
<% 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>
<%= f.label :title %><br>
<%= f.text_field :title %>
</p>
<p>
<%= f.label :text %><br>
<%= f.text_area :text %>
</p>
<p>
<%= f.submit %>
</p>
<% end %>
<%= link_to 'Back', articles_path %>
And the controller for the articles:
class ArticlesController < ApplicationController
def new
#article = Article.new
end
def create
#article = Article.new(article_params)
if #article.save
redirect_to #article
else
render 'new'
end
end
def show
#article = Article.find(params[:id])
end
def index
#articles = Article.all
end
def update
#article = Article.find(params[:id])
if #article.update(article_params)
redirect_to #article
else
render 'edit'
end
end
private
def article_params
params.require(:article).permit(:title, :text)
end
end
It does not look like you have an edit method in your Articles controller.
def edit
#article = Article.find(params[:id])
end
Just so it is clear. The edit method is what is called with the GET route that shows the form. Update is the PATCH/PUT route that takes the form in and updates the record. So, the form is shown by the edit method via GET, and processed by the update method via PUT/PATCH.
A sample code taken from http://guides.rubyonrails.org/getting_started.html
Controller
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
new.html.erb
<%= form_for :article, url: articles_path do |f| %>
<% 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>
<%= f.label :title %><br>
<%= f.text_field :title %>
</p>
<p>
<%= f.label :text %><br>
<%= f.text_area :text %>
</p>
<p>
<%= f.submit %>
</p>
<% end %>
<%= link_to 'Back', articles_path %>
A statement from this link
The reason why we added #article = Article.new in the
ArticlesController is that otherwise #article would be nil in our
view, and calling #article.errors.any? would throw an error.
My doubt:
If there is an error while filling the form, how does the #article in new know about the errors caused to the #article instance of the create action? Aren't they both different variables? And when we render 'new' shouldn't the #artcle of create method goes out of scope which holds the error description and #article of new contain no error information?
when there is any error in #article creation, there is no redirection but rendering which means that it will just render/display the new action view i.e new.html.erb without going to the new action or more precisely without making another call to new action. see this http://brettu.com/rails-daily-ruby-tip-28-whats-the-difference-between-redirect_to-and-render-in-rails/
On errors when it will render the new.html.erb it will use #article object which has all the errors which you get from these lines
#article = Article.new(article_params)
#article.save #save basically runs the validations
So basically after you submit your form, the purpose of new action is done. Now whole thing will be handled by create action in which on errors it will display the errors and uses #article object which you initialized and saved in create action and on successful creation it will make another call to show action using redirect
Hope it makes sense.
I am going through the "Getting Started with Rails Tutorial" and am stuck on update aka Edit. It is throwing the ArgumentError in Posts#edit - first argument in form can't be nil or empty. Here is the highlighted line:
First argument in form cannot contain nil or be empty
Extracted source (around line #1):
<%= form_for #post do |f| %>
It seems to have started when I implemented the partial forms part of the tutorial.
Here is the post_contoller, edit action and _forms.html respectively:
Post_controller:
class PostsController < ApplicationController
def new
#post = Post.new
end
def create
#post = Post.new(params[:post].permit(:title, :text))
if #post.save
redirect_to #post
else
render 'new'
end
end
def show
#post = Post.find(params[:id])
end
def index
#posts = Post.all
end
def update
#post = Post.find(params[:id])
if #post.update(params[:post].permit(:title, :text))
redirect_to #post
else
render 'edit'
end
end
def destroy
#post = Post.find(params[:id])
#post.destroy
redirect_to posts_path
end
private
def post_params
params.require(:post).permit(:title, :text)
end
end
Edit.html
<h1>Edit post</h1>
<%= render 'form' %>
<%= link_to 'Back', posts_path %>
_form.html
<%= form_for #post do |f| %>
<% if #post.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#post.errors.count, "error") %> prohibited
this post from being saved:</h2>
<ul>
<% #post.errors.full_messages.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>
<% end %>
The error shows an ID of "7" which is the record I am trying to update.
All other functions work (show, new, delete) and BTW "new" uses the same partial form and works fine.
Any help would be much appreciated. Thanks!
U should add this in your _controller.rb
def edit
#post = Post.find(params[:id])
end
you have to pass in the post object as local. You cannot directly access instance variables defined in controller in partial. It will be nil
<h1>Edit post</h1>
<%= render :partial => 'form', :locals => {:post => #post} %>
<%= link_to 'Back', posts_path %>
In the partial
<%= form_for post do |f| %>
check below the private is used for the below function only and write all functions above this:
private
def article_params
params.require(:article).permit(:title, :text)
end
I'm doing the Ruby on Rails tutorial at http://guides.rubyonrails.org/getting_started.html
However when I get to "5.11 Adding Some Validation", after adding the error message to display when I try to create a new post from the index view I get
"undefined method `errors' for nil:NilClass"
This is the error line highlighted.
I have already created a new Post in my new action in the controller.
Here is the source
new.html.erb
<h1>New Post</h1>
<%= form_for :post, url: posts_path do |f| %>
<% if #post.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#post.errors.count, "error") %> prohibited this post from being saved:</h2>
<ul>
<% #post.errors.full_messages.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>
<% end %>
posts_controller.rb
class PostsController < ApplicationController
def new
#Post = Post.new
end
def create
#post = Post.new(post_params)
if #post.save
redirect_to #post
else
render 'new'
end
end
def show
#post= Post.find(params[:id])
end
def index
#posts = Post.all
end
def edit
#post = Post.find(params[:id])
end
def update
#post = Post.find(params[:id])
if #post.update(post_params)
redirect_to #post
else
render 'edit'
end
end
private
def post_params
params.require(:post).permit(:title, :text)
end
end
Thanks.
Change
#Post = Post.new
To
#post = Post.new
Subtle but deadly
You've got error in your controller:
def new
#Post = Post.new
end
just change #Post to #post.