How to check if a particular param is sent via submit in Rails

I am working on rails 2.3.11.

I have a doubt in the check_box_tag

   <% form_for '', :url => { :action => 'save_subcategories' } do  %>
     <% for cat in @categories %>
     <ul class="checkboxlist" style="display:none;"  rel="<%= category.id %>">
      <% for category in categories %>
      <li>
        <%= check_box_tag "#{cat.name}[subcategory_ids][]", subcategory.id,
    category.subcategories.include?(subcategory) %><%= subcategory.name.titleize %>
      </li>
    <% end %>
    </ul>
    <% end %>
   <%= submit_tag "Save Subcategories" %>

For each category I have a list of checkboxes of subcategories which I am trying to save with a single Save button for all.

When I submit the Form - Only those categories where any of their subcategories are checked are alone sent. And it is not sent for other categories whose subcategories which are totally unchecked are not sent via params.

So in my action:

     def save_subcategories
         categories = Categoryall
         for cat in categories
           unless params["#{ cat.name }"][:subcat开发者_如何学运维egory_ids].blank?
             category_to_edit = role
         category.subcategories.clear
         subcategories=Subcategories.find(params["#{ cat.name }"][:subcategory_ids])
         category_to_edit.subcategories<<subcategories 

           end
          end
    redirect_to :action => 'index'
  end

The above code throws error as if any of my Category has none of the subcategories checked as it is not sending the category even in params.

To check if a particular parameter is in params you can do:

params.include?(:parameter)

Add this to the first line of your action to see what's getting passed in:

raise params.inspect

In general unchecked checkboxes are not sent (see check_box_tag - one to many relationship), so I suppose, if there's nothing inside the category, it's not sent too.

You could do something like this:

def save_subcategories
  categories = Category.all
  for cat in categories
    from_params = params["#{ cat.name }"]
    unless from_params.nil? || from_params[:subcategory_ids].blank?
     category_to_edit = role
     category.subcategories.clear
     subcategories = Subcategories.find(from_params[:subcategory_ids])
     category_to_edit.subcategories << subcategories 
    end
  end
  redirect_to :action => 'index'
end

I don't know what does it mean in your app when all subcategories are unchecked, but you could clear them all if no checkboxes are passed:

def save_subcategories
  categories = Category.all
  for cat in categories
    from_params = params["#{ cat.name }"]
    if from_params && from_params[:subcategory_ids].present?
      if from_params[:subcategory_ids].sort != cat.subcategory_ids.sort
        category_to_edit = role
        category.subcategories.clear
        subcategories = Subcategories.find(from_params[:subcategory_ids])
        category_to_edit.subcategories << subcategories
      end
    else
      category_to_edit = role # no idea what's that and if it's needed here...
      category.subcategories.clear
    end
  end
  redirect_to :action => 'index'
end