Ruby on rails 从另一个表中获取计数

我有一个多对多HMT模型设置，我想添加一个计数值作为我的tab_communityindex方法的一部分返回。兴趣表和联接表的模型如下所示：

class TabCommunity < ApplicationRecord
  belongs_to :ref_community_type

  has_many :tab_client_project_communities
  has_many :tab_projects, through: :tab_client_project_communities

  has_many :tab_community_accounts
  has_many :tab_accounts, through: :tab_community_accounts

  has_many :tab_client_project_communities
  has_many :ref_platforms, through: :tab_client_project_communities
end

class TabCommunityAccount < ApplicationRecord
  belongs_to :tab_community
  belongs_to :tab_account
end

我希望在ActiveRecord中复制此查询：

select (select count(*) from tab_community_accounts where tab_community_id = c.id) as cnt, c.* from tab_communities c

我想要的结果如下：

7318    149 sports_writers  7   2017-12-17 15:45:36.946965  2017-12-17 15:45:36.946965
0   172 random_admin    8   2018-04-16 19:21:21.844041  2018-04-16 19:21:21.844041
2731    173 random_aacc 7   2018-04-16 19:22:35.074461  2018-04-16 19:22:35.074461

第一列是tab_社区账户中的count*，其余列是tab_社区账户中的count*

从目前为止我所看到的情况来看，我应该使用.select或.pulk，但两者都不适合我。我试过：

TabCommunity.pluck("distinct tab_community_accounts.tab_account_id as cnt").where(id: _tab_community_ids).includes(:ref_platforms).all.order(:updated_at).reverse_order

---

这是接近我需要的还是我完全不需要了？

你想要的是：

@tab_communities = TabCommunity
  .where(id: _tab_community_ids)
  .select('tab_communities.*, count(tab_community_accounts.id) AS cnt')
  .left_outer_joins(:tab_community_accounts)
  .includes(:ref_platforms) # consider if you actually need this
  .group(:id)
  .order(updated_at: :desc) # use an explicit order instead!

.另一方面，如果查询包含多个列，则Pull只提取列值并返回一个或多个数组

@tab_communities = TabCommunity
  .where(id: _tab_community_ids)
  .left_outer_joins(:tab_community_accounts)
  .includes(:ref_platforms) # consider if you actually need this
  .group(:id)
  .order(updated_at: :desc)
  .pluck('tab_communities.id, count(tab_community_accounts.id) AS cnt')

---

将。*与Pulk一起使用不是一个好主意，因为您不知道属性在结果数组中的顺序。

您想要的是：

@tab_communities = TabCommunity
  .where(id: _tab_community_ids)
  .select('tab_communities.*, count(tab_community_accounts.id) AS cnt')
  .left_outer_joins(:tab_community_accounts)
  .includes(:ref_platforms) # consider if you actually need this
  .group(:id)
  .order(updated_at: :desc) # use an explicit order instead!

.另一方面，如果查询包含多个列，则Pull只提取列值并返回一个或多个数组

@tab_communities = TabCommunity
  .where(id: _tab_community_ids)
  .left_outer_joins(:tab_community_accounts)
  .includes(:ref_platforms) # consider if you actually need this
  .group(:id)
  .order(updated_at: :desc)
  .pluck('tab_communities.id, count(tab_community_accounts.id) AS cnt')

使用.*with pulk不是一个好主意，因为您不知道属性在结果数组中的顺序。

.left\u outer\u联接是在Rails 5中引入的。有关遗留应用程序的解决方法，请参见。Rails 5中引入了左外连接。有关遗留应用的解决方法，请参阅。

@tab_communities = TabCommunity
  .where(id: _tab_community_ids)
  .left_outer_joins(:tab_community_accounts)
  .includes(:ref_platforms) # consider if you actually need this
  .group(:id)
  .order(updated_at: :desc)
  .pluck('tab_communities.id, count(tab_community_accounts.id) AS cnt')

 (1.0ms)  SELECT tab_communities.id, count(tab_community_accounts.id) AS cnt FROM "tab_communities" LEFT OUTER JOIN "tab_community_accounts" ON "tab_community_accounts"."tab_community_id" = "tab_communities"."id" WHERE "tab_communities"."id" = 1 GROUP BY "tab_communities"."id" ORDER BY "tab_communities"."updated_at" DESC
=> [[1, 1]]