Nested attributes (Paperclip) validation - ruby-on-rails

Question

I'm working on a nested form where a user when creating a Screen should also attached an image (a separate model called Screenshot). I'm trying to validate the presence of the attachment before saving the new Screen to the db. I tried to validate the presence of the attachment in the Screenshot model, but that only precent Screenshot to be saved, while it still creates a Screen.
Here's my models:
class Screen < ActiveRecord::Base
belongs_to :project
has_many :screenshots
validates :name, presence: true
accepts_nested_attributes_for :screenshots
validates_presence_of :screenshots
end
class Screenshot < ActiveRecord::Base
belongs_to :screen
has_attached_file :image, :styles => { :medium => "300x300>", :thumb => "100x100>" }
end
here's my controller:
def create
#screen = Screen.create(screen_params)
if #screen.save
flash[:notice] = "A new screen has been added to this project"
redirect_to [#screen.project]
else
render :action => 'new'
end
end
And lastly here's my form:
<%= form_for ([#project, #screen]), :html => { :multipart => true } do |f| %>
<% if #screen.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#screen.errors.count, "error") %> prohibited this screen from being saved:</h2>
<ul>
<% #screen.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.hidden_field :project_id %>
</div>
<div class="field">
<%= f.label :name %><br>
<%= f.text_field :name %>
</div>
<div class="field">
<%= f.label :description %><br>
<%= f.text_field :description %>
</div>
<%= f.fields_for :screenshots, #screen.screenshots.build do |s| %>
<%= s.hidden_field :screen_id, :value => #screen.id %>
<%= s.hidden_field :version, :value => "1" %>
<%= s.label :image %><br>
<%= s.file_field :image %>
<% end %>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
Any help to this noob is greatly appreciated.

Answer 1

Several things for you:
Form
You shouldn't build new objects in the form itself. That needs to happen in the controller's new function
<%= f.fields_for :screenshots do |s| %>
<%= s.hidden_field :screen_id, :value => #screen.id %>
<%= s.hidden_field :version, :value => "1" %>
<%= s.label :image %><br>
<%= s.file_field :image %>
<% end %>
You can declare them like this:
def new
#screen = Screen.new
#screen.screenshots.build
#any more build declarations go here
end
Verification
I believe you should put the verification into the screnshots model, as the nested parameters are passed directly to the corresponding model. I'm not sure on that though.
In the screenshots model, I would put the validates_presence_of :screenshots, with the name as your Paperclip attachment's name