How to convert params for nested attributes and _destroy

README

Convert params in form:

    "product_suppliers_attributes"=>{
     "0"=>{"id"=>"2", "_destroy"=>"false", "supplier_id"=>"1"},
     "1"=>{"id"=>"3", "_destroy"=>"false", "supplier_id"=>"3"}
    }

to form:

    "product_suppliers_attributes"=>[
      {"id"=>"2", "_destroy"=>"false", "supplier_id"=>"1"},
      {"id"=>"3", "_destroy"=>"false", "supplier_id"=>"3"}
    ]

So you can for example use in your views:

    hidden_field_tag "product[product_suppliers_attributes][_destroy]", "true"
    check_box_tag "product[product_suppliers_attributes][_destroy]", "false"

to allow user to decide if you want to leave nested relation or delete in single table view.

application_controller.rb

class ApplicationController < ActionController::Base

  def self.convert_nested_params(*args)
    model_name = controller_name.sub(/Controller$/, '').singularize.underscore.to_sym
    options = args.extract_options!
    args.each do |nested_params_name|
      before_filter options do |controller|
        nested_params = controller.params[model_name][nested_params_name]
        if nested_params.present?
          logger.info "Converting params for #{model_name}, nested_params: #{nested_params.inspect}"
          params[model_name][nested_params_name] = nested_params.inject([]) do |acc,el|
            acc << el.last
          end
          logger.info "Params after conversion: #{params.inspect}"
        end
      end
    end
  end 

end

products_controller.rb

class ProductsController < ApplicationController
  convert_nested_params :product_suppliers_attributes, :only => [:create, :update]
end