define column default in app/models/*.rb

gistfile1.rb

class Person < ActiveRecord::Base
  def self.column_default_values(defs)
    defs.each do |cname, value|
      columns.detect{|c| c.name.to_sym == cname.to_sym }.instance_variable_set('@default', value)
    end
  end

  column_default_values(name: 'hibariya')
end