Question

I have list with posts (pages#home), on click I open list with comments (posts#show), where I declare variable @feed_items. In the end of the comments I have simple_form for new comment (comments#create). Problem: if error occuring on submit button, I need to render existed list with comments and form with errors.
I’m trying in comments#create:

if @comment.save
  ...
else
  render 'posts/show'
end

but in this case variable @feed_items isn’t declared because method posts#show didn’t called. When I trying to write redirect_to I see list with comments but without error messages. How to do this?

Answer 1

This is a common mistake people do. The render method only selects the view to display, and the redirect_to method executes the action of the redirection again.
When there are errors, you call the render method to select the view you want to display, and you have to manually assign all the instance variables this view need to work out.
Check Section 2.3.2 from the rails guides: http://guides.rubyonrails.org/layouts_and_rendering.html

In your case it would be something like this:

if @comment.save
  ...
else
  # Populate the @feed_items in here again
  render 'posts/show'
end