ruby-on-rails - 如何在此迁移中编写向下或可逆函数？

Question

因此，如果此迁移导致任何错误，我希望能够恢复/rake db:rollback。

编码：

class ChangeUidToPrimaryKey < ActiveRecord::Migration
def change
execute ALTER TABLE "users" DROP CONSTRAINT "users_pkey".
execute ALTER TABLE "users" ADD PRIMARY KEY "uid"
end
end

在这种情况下，我可以添加哪些向下/可逆代码来使 rake db:rollback 工作？

Answer 1

email如果您需要恢复， 您可以执行以下操作，即保持唯一索引。

class ChangeUidToPrimaryKey < ActiveRecord::Migration
  def self.up
    execute "alter table users add constraint unique_users_email unique(email)"
    execute "ALTER TABLE users DROP CONSTRAINT users_pkey"
    execute "ALTER TABLE users ADD PRIMARY KEY (uid)"
  end

  def self.down
    execute "ALTER TABLE users DROP CONSTRAINT users_pkey"
    execute "ALTER TABLE users DROP CONSTRAINT unique_users_email"
    execute "ALTER TABLE users ADD PRIMARY KEY (email)"
  end
end