Rails回形针无法从另一个视图访问图像

Question

my app has an habtm relation b/w listings and categories. now from the categories index page, a user filters select box to view listings in the show page.

now i am not able to access images attached to listings in the category show page.

listing.rb

attr_accessible :placeholder, :categories_ids

  has_and_belongs_to_many :categories
  has_attached_file :placeholder, :styles => { :medium => "300x300>", :thumb => "100x100>" }, :default_url => "/images/:style/missing.png",
                      :url => "/system/:hash.:extension",
                     :hash_secret => "longSecretString"

categories controller

def index
  @categories = Category.all
end

def show
  @categories = Category.find_by_sql ["select distinct l.* from listings l , categories c, categories_listings cl where c.id = cl.category_id and l.id = cl.listing_id and c.id in (?,?)" ,  params[:c][:id1] , params[:c][:id2]]
end

the sql just filters and displays the listings in show page where i can show its attributes, but cant access the placeholder. note the plural @categories in show

categories show page

<ul>
  <% @categories.each_with_index do |c, index| %>
  <% if  index == 0 %>
    <li class="first"><%= c.place %></li>

    <%= image_tag c.placeholder.url(:thumb) %>

    <li><%= c.price %></li>

    <% else %>
    <li><%= c.place %></li>
    <li><%= c.price %></li>

    <%= image_tag c.placeholder.url(:thumb) %>
    <% end %>

  <% end %>
</ul>

Access image from different view in a view with paperclip gem ruby on rails

this said to make the object plural and call a loop, wch shall allow to access the image.

it does not work in this case.

undefined method `placeholder' for #<Category:0x5c78640>

but the amazing thing is, placeholder will be displayed as an array of all images for all the listings if used as suggested in that stackoverflow, wch is, obviously, not the way i prefer. where's the issue? what am i missing?

Answer 1

Having looked at your code, the immediate issue I can see is that placeholder is part of the listing.rb model, not category.rb

---

ActiveRecord Objects

When you call an ActiveRecord object (eg @categories = Category.all ), the ActiveRecord object is created on the Category model, which means any dependencies from that will have to be accessed like an array -> @categories.listings

The associations of these records are created with the various has_and_belongs_to_many associations you created in your models, which seem to be working correctly

So my recommendation is to call listings as a dependency of Category, like this:

<%= image_tag c.listings.first.placeholder.url(:thumb) %>

---

Update

To show all the images for the listings, you will have to just do an .each loop, like this:

<ul>
  <% @categories.each_with_index do |c, index| %>
  <% if  index == 0 %>
        <li class="first"><%= c.place %></li>

        <% c.listings.each do |listing| %>
            <%= image_tag listing.placeholder.url(:thumb) %> 
        <% end %>

        <li><%= c.price %></li>
    <% else %>
        <li><%= c.place %></li>
        <li><%= c.price %></li>

        <% c.listings.each do |listing| %>
            <%= image_tag listing.placeholder.url(:thumb) %> 
        <% end %>

    <% end %>

  <% end %>
</ul>

---

ActiveRecord & Paperclip

I think the conclusion is this:

Your SQL query is bringing back the "pure data" from your listings database. That's fine, but you want to use Paperclip's .url function, which only fires with ActiveRecord (it creates an image object & attaches to the ActiveRecord object)

Your listings db has these columns:

• placeholder_file_name
• placeholder_content_type
• placeholder_file_size
• placeholder_updated_at

These cannot create an image output for you, as the image file is stored in a different path to the placeholder_file_name

When you use Paperclip, it takes the data stored in these columns & creates an ActiveRecord image object, which you can then call by using c.listings.first.placeholder.url . Notice how the placeholder column is not in the database at all; meaning Paperclip needs to be called by ActiveRecord before you can use its functionality

You could use a query like this (this is a complete stab in the dark to be honest, but hope it gives you more insight):

@categories = Category.joins(:listings).where(:id => [params[:c][:id1],params[:c][:id2]])