置换＆QUOT;的has_many ... counter_sql＆QUOT;在Rails的4.1 [英] Replacement for "has_many ... counter_sql" in Rails 4.1

问题描述

Rails的4.1去掉了 counter_sql 从的has_many 的关联，所以下面就不再起作用：

Rails 4.1 removed the counter_sql from has_many associations, so the following does no longer work:

class Project < ActiveRecord::Base

  has_many :backers,
    -> { select('COMPLEX SQL QUERY') },
    through: :pledges,
    source: :backer,
    counter_sql: proc { "COMPLEX COUNT SQL QUERY" }

  (...)
end

我需要一个 counter_sql 在这里，因为有复杂的SQL查询选择，AR没有建立有效的SQL时，我做的 project.backers.count 。

I need a counter_sql here since with the COMPLEX SQL QUERY in select, AR does not build valid SQL when I do project.backers.count.

要解决这个问题，我想提出这个到像这样的方法：

To fix this, I'd move this to a method like so:

class Project < ActiveRecord::Base

  has_many :backers,
    -> { select('COMPLEX SQL QUERY') },
    through: :pledges,
    source: :backer

  def backers_count
    self.class.count_by_sql 'COMPLEX SQL QUERY'
  end

  (...)
end

这是一个很好的方式去还是有其他更好的办法？

Is this a good way to go or are there better approaches?

推荐答案

您可以使用关联的扩展

class Project < ActiveRecord::Base
  has_many :backers,
    -> { select('COMPLEX SQL QUERY') },
    through: :pledges,
    source: :backer do

    def count
      #query here
    end
  end
end

该协会代理可作为 proxy_association ，特别是 proxy_association.owner 返回项目对象。

The association proxy is available as proxy_association, in particular proxy_association.owner returns the project object.

这将覆盖默认提供的计数方法，所以 some_project.backers.count 将调用您的自定义查询

This overwrites the count method provided by default, so some_project.backers.count will call your custom query

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