在Rails遷移中的rename_column後保存

Question

我正在嘗試解決Oracle無法更改其中包含數據的列的類型。我緩存屬性的正確值，將其設置爲無，重命名列，然後嘗試重新設置屬性：

class SwitchToForeignKeys < ActiveRecord::Migration 
    def self.up 
    registration_countries = {} 
    Registration.all.each do |r| 
     if c = Country.find_by_name(r.country) 
     registration_countries[r.id] = c.id 
     r.country = nil 
     r.save 
     end 
    end 

    rename_column :registrations, :country, :country_id 
    change_column :registrations, :country_id, :integer 

    Registration.reset_column_information 
    registration_countries.each do |reg_id, country_id| 
     r = Registration.find(reg_id) 
     r.reload 
     r.country_id = country_id 
     r.save 
    end 
    end 
end 

在運行遷移我上第二r.save此錯誤：

undefined method `country' for #<Registration:0x7f409698be48> 

Answer 1

一個解決辦法是使用執行：

registration_countries.each do |reg_id, country_id| 
    execute "UPDATE registrations SET country_id = '#{country_id}' WHERE id = #{reg_id}" 
end 
execute "commit"