Question

I have an array of @pages below

#<Page id: 1, url: "/location1", name: "Information", sort_order: 2, parent_id: nil>
#<Page id: 2, url: "/location2", name: "Information 2", sort_order: 2, parent_id: 4>
#<Page id: 3, url: "/location3", name: "Information 3", sort_order: 1, parent_id: >
#<Page id: 4, url: "/location4", name: "Information 4", sort_order: 1, parent_id: nil>
#<Page id: 5, url: "/location5", name: "Information 5", sort_order: 1, parent_id: 2>
#<Page id: 6, url: "/location6", name: "Information 6", sort_order: 3, parent_id: nil>

And i am trying to build a nav with these pages…Note this is just an example I really have 70 pages similar to this

I want the final outcome to look like this

<ul>
  <li><a href="/location4">Information 4</a>
    <ul>
      <li><a href="/location3">Information 3</a></li>
      <li><a href="/location2">Information 2</a>
        <ul><li><a href="/location5">Information 5</a></li></ul>
      </li>
    </ul>
  </li>
  <li><a href="/location1">Information 1</a></li>
  <li><a href="/location6">Information 6</a></li>
</ul>

So the parent_id will signal if the li has another child ul and li and the sort order is the ordering of the chil li’s

I cant seem to wrap my brain around how i need to loop over @pages efficiently …any ideas..

Answer 1

Start with only top level Pages, i.e. Pages where parent_id == nil, ordered by sort_order

Define a children method that gets you all Pages where parent_id == self.id, ordered by sort_order

Then you should be able to do something like this:

def build_navigation(pages, html = nil)
  return "" if pages.length == 0

  navigation_html = html || ""
  navigation_html << "<ul>"

  pages.each do |page|
    navigation_html << li_tag(page)
    navigation_html << build_navigation(page.children, navigation_html)
  end

  navigation_html << "</ul>"
end

def li_tag(page)
  "<li><a href='#{page.name}'>#{page.name}</a></li>"
end

build_navigation(parent_pages).html_safe

Update:
Slightly adapted so it works when you only want to do ONE query:

def all_pages
  # get all the pages from the DB
end

def parent_pages(pages)
  parents = pages.reject { |page| page.parent_id.nil? }
  sort(parents)
end

def children(parent, pages)
  children = pages.map { |page| page.parent_id == parent.id }
  sort(children)
end

def sort(pages)
  pages.sort { |a, b| a.sort_order <=> b.sort_order }      
end

def build_navigation(pages, html = nil)
  return "" if pages.length == 0

  navigation_html = html || ""
  navigation_html << "<ul>"

  pages.each do |page|
    navigation_html << li_tag(page)
    navigation_html << build_navigation(children(page, all_pages), navigation_html)
  end

  navigation_html << "</ul>"
end

def li_tag(page)
  "<li><a href='#{page.name}'>#{page.name}</a></li>"
end

build_navigation(parent_pages(all_pages)).html_safe