Implementing Rails helper method: Nested hash tree to nested HTML list

Question

I am trying to convert a nested hash tree to nested HTML list. So far I've created Post and Tag model and implemented hierarchy to the Tag model using Closure Tree .

Following is the helper method I've found from another post to make a recursive method to render hash to a nested set of list:

def hash_list_tag(hash)
  html = content_tag(:ul) {
    ul_contents = ""
    ul_contents << content_tag(:li, hash[:parent])
    hash[:children].each do |child|
      ul_contents << hash_list_tag(child)
    end

    ul_contents.html_safe
  }.html_safe
end

I just inserted this code to my helper section (application_helper.rb) without changing anything.

Afterwards, I embedded the following inside the view page(index.html.erb) to render a hash to a nested HTML list:

<div>
  <% hash_list_tag Tag.hash_tree do |tag| %>
    <%= link_to tag.name, tag_path(tag.name) %>
  <% end %>
</div>

However, I received this error:

ActionView::Template::Error (undefined method `each' for nil:NilClass):
    1: 
    2: 
    3: <div>
    4:   <% hash_list_tag Tag.hash_tree do |tag| %>
    5:     <%= link_to tag.name, tag_path(tag.name) %>
    6:   <% end %>
    7: </div>
  app/helpers/application_helper.rb:14:in `block in hash_list_tag'
  app/helpers/application_helper.rb:11:in `hash_list_tag'
  app/views/posts/index.html.erb:4:in `_app_views_posts_index_html_erb__1316616690179183751_70207605533880'

Sadly I'm not at a level to write my own helper methods, I found this helper method from another post. This is the link <stackoverflow.com/questions/14904772/…>. I'll greatly appreciate if you could help me what I should do to fix this or advise me if there's other way to call the descendants of root nodes. — wag0325
– wag0325, Commented Jan 26, 2014 at 2:30

Roobie Nuby · Accepted Answer · 2014-01-26 02:38:01Z

0

When you do

hash[:children].each do |child|

and there are no children, the result is a nil, which has no method called each. (Read the error message). So you need to check for this case:

if !(hash[:children].nil?)
  hash[:children].each do |child|

answered Jan 26, 2014 at 2:38

Roobie Nuby

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1 Comment

wag0325 Over a year ago

This removed the error, but I don't see my list on the index page. I'm double checked from 'rails console' that Tag.hash_tree generates nested hash.

Bhushan Ahire · Accepted Answer · 2016-12-09 15:17:15Z

0

With closure tree you dont get hash with :parent and :children keys. Below code will solve your issue.

html = content_tag(:ul) {
    ul_contents = ""
    hash.each do |key, value|
      ul_contents << content_tag(:li, key)
      if value.present?
        value.each do |child|
          ul_contents << hash_list_tag(child)
        end
      end
    end

    ul_contents.html_safe
  }.html_safe

answered Dec 9, 2016 at 15:17

Bhushan Ahire

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