Rails 5.2部分计数器：“未定义的局部变量或方法”错误

Question

Per the information box on https://guides.rubyonrails.org/layouts_and_rendering.html#using-partials :

Rails also makes a counter variable available within a partial called by the collection, named after the title of the partial followed by _counter. For example, when rendering a collection @products the partial _product.html.erb can access the variable product_counter which indexes the number of times it has been rendered within the enclosing view.

However, I am getting and error when referencing the counter in my partial. Here is the parent view:

<%= render partial: 'comments/comment_template', collection: @post.comments, as: :c %>

Here is the relevant part of _comment_template.html.erb :

<%= comment_template_counter %>

And here is the error:

undefined local variable or method `comment_template_counter' for #<#<Class: [etc.]

What am I missing?

Answer 1

I believe the documentation is incorrect. As pointed out by pedroadame at https://coderwall.com/p/t0no0g/render-partial-with-collection-has-hidden-index , when using the :as option, I need to use the name of the variable rather than the name of the partial .

Furthermore, if elsewhere in my app I am only rendering the partial once instead of as a collection, I need to sidestep the (same) error message by checking whether the counter is defined.

So in my partial, this now works:

<%= c_counter if defined? c_counter %>