Question

I have an app where I know

def new 
    respond_to do |format|
      format.html { new_or_edit }
      format.js { 
        @category = Category.new
      }
    end  
end

is being called when I click a link.

This leads to new_or_edit being called (defined in the same file).

  def new_or_edit
    @categories = Category.find(:all)
    @category = Category.find(params[:id])
    @category.attributes = params[:category]
    if request.post?
      respond_to do |format|
        format.html { save_category }
        format.js do 
          @category.save
          @article = Article.new
          @article.categories << @category
          return render(:partial => 'admin/content/categories')
        end
      end
      return
    end
    render 'new'
  end

After some tests, I find that the each execution stops at

@category = Category.find(params[:id])

with the error “Couldn’t find Category without an ID”. Params doesn’t have an :id hash when I printed it out. Is this because I have to save it into the database before the default :id field is created?

Answer 1

What you are doing wrong is trying to unify two inherently different actions: new and edit.

params is a hash of parameters you get from the client.

When you create a new object, params[:id] is left blank since the id attribute of a newly created object is the responsibility of the server, not the client.

When you edit an existing object, params[:id] is not blank since the object already exists in the database and has an id. The meaning of params[:id] here is “Please edit object with id param[:id] using these attributes”.

After explaining this, when you create a new object this line:

@category = Category.find(params[:id])

Fails since params[:id] is empty.