Rails 4 strong params and nested form - ruby-on-rails

Question

I'm building a simple app (Ruby 2.0.0 and Rails 4) where a user can create a project and for each project create multiple screens. When creating a screen the user can upload a screenshot, that refer to a its own model (I do this to handle multiple versions of the same screen).
When creating the screen, the screenshot doesn't seem to be created because of a permission problem. Here's the server log:
Processing by ScreensController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"kezaGADsaLmY/+zozgbjEe5UfdeqRPg58FCf1qzfHxY=", "screen"=>{"project_id"=>"24", "name"=>"Billing", "description"=>"This is the page where a user will enter their credit card information", "screenshot"=>{"image"=># <ActionDispatch::Http::UploadedFile:0x007fcdce25b2c0 #tempfile=#<Tempfile:/var/folders/pv/srwrv0qj35b0hsxkt42l_z500000gn/T/RackMultipart20131007-91790-tewse9>, #original_filename="fb-banner.png", #content_type="image/png", #headers="Content-Disposition: form-data; name=\"screen[screenshot][image]\"; filename=\"fb-banner.png\"\r\nContent-Type: image/png\r\n">}}, "commit"=>"Create Screen"}
Unpermitted parameters: screenshot
These are my models:
Screen
class Screen < ActiveRecord::Base
belongs_to :project
has_many :screenshots
validates :name, presence: true
accepts_nested_attributes_for :screenshots
end
Screenshot
class Screenshot < ActiveRecord::Base
belongs_to :screen
end
This is my screens_controller:
class ScreensController < ApplicationController
before_action :set_screen, only: [:show, :edit, :update, :destroy]
def index
#screens = Screen.all
end
def show
end
def new
#screen = Screen.new(:project_id => params[:project_id])
#screen.screenshot.build
end
def edit
end
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
def update
#screen = Screen.find(params[:id])
if #screen.update_attributes(screen_params)
flash[:notice] = "The screen has been successfully updated"
redirect_to [#screen.project]
else
render :action => 'edit'
end
end
def destroy
#screen = Screen.find(params[:id])
#screen.destroy
flash[:notice] = "Successfully destroyed screen"
redirect_to [#screen.project]
end
private
def set_screen
#screen = Screen.find(params[:id])
end
def screen_params
params.require(:screen).permit(:project_id, :name, :description, screenshot_attributes: [ :id, :screen_id, :image, :version ])
end
end
And finally this is the form:
<%= form_for #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 :screenshot 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 %>
I hope this is enough to help me spot the problem. I'm a newbie when it comes to programming, so any help is more than welcome.

Answer 1

I recently worked through something similar, and this is what seemed to work...
Change your fields_for to plural:
<%= f.fields_for :screenshots do |s| %>
And also, make your params
def screen_params
params.require(:screen).permit(:project_id, :name, :description, screenshots_attributes: [ :id, :screen_id, :image, :version ])
end
Also, you need to update your new action to make screenshots plural, like so:
def new
#screen = Screen.new(:project_id => params[:project_id])
#screen.screenshots.build
end