Postgres change column string to integer

postgres_change_column_string_to_integer.rb

class ChangeColumnOnMovementShipmentDvcaAndDvcu < ActiveRecord::Migration
  def change
    rename_column :movement_shipments, :dvca, :dvca_s
    rename_column :movement_shipments, :dvcu, :dvcu_s

    add_column :movement_shipments, :dvca, :decimal, default: 0
    add_column :movement_shipments, :dvcu, :decimal, default: 0

    MovementShipment.reset_column_information
    MovementShipment.find_each { |c| c.update_attributes({
      dvca: c.dvca_s,
      dvcu: c.dvcu_s
    }) }

    remove_column :movement_shipments, :dvca_s
    remove_column :movement_shipments, :dvcu_s
  end
end