Find previous or next array - ruby-on-rails

Question

I created a rails app that allows the user to read a magazine.
To do so, I created two scaffolds, one for the magazine and an other for the pages inside of it. I then made a one-to-many relationship, so the pages belong to the magazine.
Each page is an image, since they are digitized then uploaded in a multi-upload form.
Recently, the group I work for asked me to find a way to allow the user to read two pages at the same time, so I made some tweaks, and it works like a charm.
However, I now have a problem: I want to set some "previous" and "next" links, but I can't find a way to do so
Here is what I have done so far:
magazine_controller.rb
def create
#magazine = Magazine.new(magazine_params)
if #magazine.save
#index = 0
(params[:images] || []).each_with_index do |image, index|
if index.even?
#This way, #index increments every other upload
#So I'm sure I have two images with the same page_number
#index += 1
end
#magazine.pages.create(image: image, page_number: #index)
end
redirect_to #magazine, notice: 'Magazine créé'
else
render :new
end
end
models/page.rb
class Page < ApplicationRecord
belongs_to :magazine
validates_presence_of :magazine
mount_uploader :image, PageUploader
def previous
self.class.first.where('page_number < ?', page_number).limit(1).first
end
def next
self.class.first.where('page_number > ?', page_number).limit(1).last
end
end
views/pages/show.html.erb
<% #page.each do |p| %>
<%= image_tag p.image %>
<%= p.inspect %>
<% end %>
<br />
<%= #page.first.page_number %>
<%= link_to '< Précédent', magazine_page_path(magazine_id: #magazine.slug, id: #page.previous) if #page.previous %>
<%= link_to 'Suivant >', magazine_page_path(magazine_id: #magazine.slug, id: #page.next) if #page.next %>
<br />
<%= link_to 'Back', magazines_path %>
page_controller.rb
private
def set_page
#magazine = Magazine.find_by(slug: params[:magazine_id])
#was 'find_by' before I was asked to show two records at the same time
#page = #magazine.pages.where(page_number: params[:id])
end
So with this code, I'm getting the error undefined method 'previous' for #<Page::ActiveRecord_AssociationRelation:0x007ff4f702ad48>. I don't have a clue about how to find if there is a following "page" or not.
Any idea welcome!
Thank you in advance

Answer 1

Remember that #page is no longer a single record, it's an association with two records.
You can create previous and next page methods in Page class for the association instead of the object (self.previous instead of previous). It will get a new association for the previous (or next) page number. Note the addiitional code to make sure you're getting the same magazine (which you don't have in your current code that worked for single pages).
Also note that if the association has no records (count == 0) the methods return nil... this is to accommodate your if #page.previous test for no previous (and if #page.next if no next)
def self.previous
new_page_set = Page.where(page_number: (first.page_number - 1), magazine: first.magazine)
return new_page_set.count == 0 ? nil : page_set
end
def self.next
new_page_set = Page.where(page_numberL (first.page_number + 1), magazine: first.magazine)
return new_page_set.count == 0 ? nil : page_set
end