Question

I have a form for creating a model (named Image) and the list for all entities of this model on the same view. The model is associated in a one-to-many relation with a second model called Deck (one Deck has many Images). The list in my view looks like this:

# image list    
<% @deck.images.each  do |img| %> # iterates also through invalidated model
    <%= link_to 'Delete', deck_image_path(@deck, img), 
           :confirm => 'Sure?', :method => :delete %>
<% end %>

My problem occurs when the validation for the @image object fails. The iteration iterates also through the invalid image object and gives an error for the next line saying there is no such path for that object.

I could check every object for .new_record?, but is this the preferred way? Or am I doing something absolutely wrong? I have nobody else seen with such a problem ;/

Update 1 – Controller

def create
    @deck = Deck.find(params[:id])
    @image = @deck.images.build(params[:image])

        respond_to do |format|
            if @image.save
              # redirect
              flash[:notice] = "Saved succesfully."
              format.html { redirect_to(@deck) }
            else
              # render
              format.html { 
                flash.now[:error] = "Could not be saved."
                render 'decks/show'
              }
        end
    end
end

Update 2 – More confusion

Well, ok I am absolutely confused now. Changing the second line in the create method from

# not working
@image = @deck.images.build(params[:image])

to

# working
@image = Image.new(params[:image])
@image.deck = @deck

seems to work without any errors. What is the difference?

Update 3 – View and error message

<h3>Upload Image</h3>
<%= form_for @image, :url => deck_images_path(@deck), :html => { :multipart => true } do |form| %>
<fieldset>
    <legend>Upload new image</legend>
    <%= render :partial => 'shared/model_errors', :locals => {:model => @image} %>
    <%= form.file_field :image %><br/>
    <%= form.submit "Upload", :class => 'btn btn-primary' %>
</fieldset>
<% end %>

<h3>Show all existing images</h3>
<% @deck.images.each  do |img| %>
    <%= image_tag img.image.url %>  
    <%= link_to 'Delete'.html_safe, deck_image_path(@deck, img) %>
<% end %>

The error message:

No route matches {:controller=>"images", :action=>"destroy", :deck_id=>#<Deck id: 1, 
name: "Test", description: "Test", created_at: "2012-12-10 20:44:22", 
updated_at: "2012-12-10 20:44:22">, :id=>#<Image id: nil, created_at: nil, 
updated_at: nil, image_file_name: nil, image_content_type: nil, 
image_file_size: nil, image_updated_at: nil, deck_id: 1>}

Answer 1

According to [1]: Build vs new in Rails 3 parent_model.children.build oder parent_model.children.new seems to create a relationship in memory instantly. So parent_model.children gets filled with a new children model having its parent_id = parent.

The alternative with Children.new seems to add this new relationship after saving the new child object. Therefore its missing in an iteration over all children.