Nested forms for belongs_to relationship - ActiveAdmin

For my current project I had to add nested form for belongs_to relationship. After lots of searching i found a solution.

class Product < ActiveRecord::Base

 belongs_to :cost, :class_name => 'Currency', foreign_key: 'cost_id'

 accepts_nested_attributes_for :cost

 attr_accessor :cost_id

end

class Currency < ActiveRecord::Base

 def self.currency_types

   ['SAR','AED','USD','EUR','INR']

 end
end

ActiveAdmin.register Product do

 form do |f|

    f.semantic_errors *f.object.errors.keys

    f.inputs "Details" do

      f.input :name

      f.inputs "cost" do

         f.semantic_fields_for :cost_attributes  do |j|

            j.inputs do

              j.input :currency_type, :as => :select, :collection => Currency.currency_types,:label =>'Cost'

              j.input :value

            end

          end

        end

      end

    end

    f.actions

 end

 controller do

   def permitted_params

    params.permit product: [:name,cost_attributes:[:id,:currency_type,:value]]

   end

 end
end