controller.rb

  # my controller
  
    def create
    @uid = Uid.find_by(number: uid_params[:number])
    if @uid
      update
    else
      @uid = Uid.new(uid_params)
      if @uid.save
        puts "Uid is #{@uid.inspect}"
        flash[:success] = "Successfully created post"
        redirect_to uids_path
      else
        @uids = Uid.paginate(page: params[:page])
        render :index
      end
    end
  end

  def update
    @uid = Uid.find_by(number: uid_params[:number])
    if @uid.update_attributes(uid_params)
      flash[:success] = "Successfully created post"
      redirect_to uids_path
    else
      @uids = Uid.paginate(page: params[:page])
      render :index
    end
  end


# my modal

class Uid < ActiveRecord::Base

  before_save :check_number_validity

  has_many :microposts, dependent: :destroy, autosave: true
  accepts_nested_attributes_for :microposts

  validates :number, presence: true, length: { is: 12 }, format: { with: /\A\d{12}\z/ }, uniqueness: true

  private

    def check_number_validity
      # to check for number validity
      true
    end
end


# my micropost model
class Micropost < ActiveRecord::Base

  belongs_to :uid

  default_scope -> { order('created_at DESC') }

  validates :content, presence: true, length: { maximum: 256 }
  validates :uid_id, presence: true
end