Blank value can't be saved if chosen in select field. (Gem Ancestry)

Question

I'm using Rails 4.0.1 with Ruby 2.0.0. I have a simple functionality of categories. Each category could belong to another one or be a root category (no parent). But if choose blank ('None') value from select, category can not be saved. Where is my mistake?

category.rb

class Category < ActiveRecord::Base

  has_many :items
  has_ancestry

  validates :name, presence: true, length: { minimum: 3 }
  mount_uploader :icon, IconUploader

end

categories_controller.rb

def create
  @category = Category.new(category_params)
  if @category.save 
    redirect_to admin_categories_path, notice: "Category was successfully created!"
  else
    render action: "new"
  end
end

_form.html.slim

= form_for [:admin, @category] do |f|
  = f.label :name
  = f.text_field :name

  = f.label :ancestry
  = f.select :ancestry, Category.all.map {|p| [ p.name, p.id ] }, include_blank: 'None'

  = f.label :icon
  = f.file_field :icon

  = f.submit nil

Transaction log

Started POST "/admin/categories" for 127.0.0.1 at 2014-01-11 12:18:35 +0600
Processing by Admin::CategoriesController#create as HTML
Parameters: {"utf8"=>"✓",    "authenticity_token"=>"aZS2bO2HEy65cf2jQmm5BTy1VS/1Na1LBN4mHR3FYy4=", "category"=>{"name"=>"Example", "ancestry"=>""}, "button"=>""}
(0.1ms)  begin transaction
(0.1ms)  rollback transaction

Answer 1

I just came across the same problem. Instead of trying to set the ancestry field on your model, use parent_id instead.

So in your form, use this:

= f.label :parent_id
= f.select :parent_id, Category.all.map {|p| [ p.name, p.id ] }, include_blank: 'None'

Then in your controller, edit the category_params function to allow the attribute to be assigned:

def category_params
  params.require(:category).permit(:name, :parent_id)
end