如何获得可在rake任务中运行的Rails控制台中工作的Active Record查询？

Question

我有一个活动记录查询，该查询在控制台中工作正常，但在rake任务中使用它时不起作用

这是我耙任务的开始：

namespace :attendees do
  desc "Migrate sms plans to receive_sms attribute for attendees"
  task migrate_sms_plans: :environment do
    attendees_with_sms_plans = Attendee.select('attendees.id, attendees.phone, attendees.local_phone').joins(:plans).where('plans.name = ?', "Yes! SMS!")

为什么select语句可以在我的rails控制台中工作，但在rake任务中使用它时却出现以下错误，以及如何解决：

ActiveRecord::StatementInvalid: PG::UndefinedFunction: ERROR:  function count(integer, character varying, character varying) does not exist
LINE 1: SELECT COUNT(attendees.id, attendees.phone, attendees.local_...
               ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

原来错误不是select语句，而是下一行：

puts <<-TEXT
    Going to migrate #{attendees_with_sms_plans.count} attendees from "Yes! SMS!" plan to receive_sms: true attribute on Attendee Model
TEXT

我通过更改为：

puts <<-TEXT
    Going to migrate #{attendees_with_sms_plans.to_a.count} attendees from "Yes! SMS!" plan to receive_sms: true attribute on Attendee Model
TEXT

Answer 1

到目前为止，您猜错了：-

attendees_with_sms_plans = Attendee.select('attendees.id, attendees.phone, attendees.local_phone').joins(:plans).where('plans.name = ?', "Yes! SMS!")

Attendee::ActiveRecord_Relation attendees_with_sms_plans结果将与Attendee::ActiveRecord_Relation

并在调用attendees_with_sms_plans.count会导致

错误：函数计数（整数，字符变化，字符变化）不存在

这意味着Postgres不支持不止一列的count（）

所以解决方案是您可以使用size()来代替count()如下所示：-

attendees_with_sms_plans.size

Answer 2

请通过以下查询检查功能计数是否存在

SELECT n.nspname
FROM pg_extension e
   JOIN pg_namespace n
      ON e.extnamespace = n.oid
WHERE e.extname = 'count';

如果不在search_path ，则查询将找不到该函数。

要在其他架构中使用扩展，请在以下示例中将其拖放并重新创建：

DROP EXTENSION count;
CREATE EXTENSION count SCHEMA public;