ruby-on-rails - Rails 4 迁移将列数据类型从字符串更改为整数并保留数据 (postgres)

Question

我需要将字符串字段转换为整数并使用enum代替。在不丢失数据的情况下执行此操作的最佳方法是什么？

这是当前的迁移:

class CreateSystems < ActiveRecord::Migration
  def change
    create_table :systems do |t|
      t.string :operation
      t.string :status

      t.timestamps null: false
    end
  end
end

然后我更改字段的类型，如下所示:

class ChangeColumnsForSystems < ActiveRecord::Migration
  def change
    change_column :systems, :operation, :integer
    change_column :systems, :status, :integer
  end
end

并更新模型文件。

/app/models/system.rb

...
enum operation { start: 0, stop: 1 }
enum status { init: 0, working: 1, complete: 2 }
...

如何更新旧数据？

Answer 1

经过一番研究，我发现这是一个合适的解决方案。

class ChangeColumnsForSystems < ActiveRecord::Migration
  def change
    change_column :systems, :operation, "integer USING (CASE operation WHEN 'start' THEN '0'::integer ELSE '1'::integer END)", null: false
    change_column :systems, :status, "integer USING (CASE status WHEN 'init' THEN '0'::integer WHEN 'working' THEN '1'::integer ELSE '2'::integer END)", null: false
  end
end

更新:在某些情况下，您必须在更改类型之前删除默认值。这是带有回滚功能的版本。

class ChangeColumnsForSystems < ActiveRecord::Migration
  def up
    change_column_default :systems, :status, nil
    change_column :systems, :operation, "integer USING (CASE operation WHEN 'start' THEN '0'::integer ELSE '1'::integer END)", null: false
    change_column :systems, :status, "integer USING (CASE status WHEN 'init' THEN '0'::integer WHEN 'working' THEN '1'::integer ELSE '2'::integer END)", null: false, default: 0
  end

  def down
    change_column_default :systems, :status, nil
    change_column :systems, :operation, "varchar USING (CASE operation WHEN '0' THEN 'start'::varchar ELSE 'stop'::varchar END)", null: false
    change_column :systems, :status, "varchar USING (CASE status WHEN '0' THEN 'init'::varchar WHEN '1' THEN 'working'::varchar ELSE 'complete'::varchar END)", null: false, default: 'init'
  end
end