Instance variable vs local variable in the Create method

Question

As far as I understand we use namely an instance variable in the method new

def new
  @article = Article.new
end

because this variable is used in new.html.erb too. (Please correct me if I am wrong).

But why do we use an instance variable in the create method? Where else is it used outside the create method? Can't we just use a local variable article instead of the instance variable @article?

def create
  article = Article.new(article_params)

  if article.save
    flash[:success] = "Article created successfully!"
    redirect_to  articles_url
  else
    render 'new'
  end 
end

private  
def article_params
   params.require(:article).permit(:title, :body)
end

Mirko Akov · Accepted Answer · 2014-02-25 13:05:26Z

3

This means that you don't understand render :new.

This line means that the view for the new method will be rendered, but the method itself will NOT be invoked. That's why you need the variable to be instance variable, because if the validations fails, you will need it to pass it to form.

Take a look at the guides for more information

PS render :new is the same as render 'new'

answered Feb 25, 2014 at 13:05

Mirko Akov

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Marek Lipka · Accepted Answer · 2014-02-25 12:58:32Z

1

You can't, because @article variable is also used in new.html.erb file, rendered when article isn't saved successfully.

So you'll get (as far as I remember) error undefined method 'model_name' for nil:NilClass.

answered Feb 25, 2014 at 12:58

Marek Lipka

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1 Comment

fade2black Over a year ago

Yeah, you are right. It is used by new. I've just figured out it, when my rspec-test failed and so it rendered the new. Since I used a local version of article it ended up with an error message. Thanks.

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