如何查询关联模型上的对象数量？

Question

我有一个 Profile 和那个 has_many :ratings。

我想要查找的是 Profile 个对象的数量，这些对象具有超过 1 个与之关联的评级记录。

我尝试了以下方法无济于事：

> Profile.includes(:ratings).where('ratings.count > 0').count
   (38.2ms)  SELECT COUNT(*) FROM "profiles" WHERE (ratings.count > 0)
ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR:  missing FROM-clause entry for table "ratings"
LINE 1: SELECT COUNT(*) FROM "profiles" WHERE (ratings.count > 0)
                                               ^
: SELECT COUNT(*) FROM "profiles" WHERE (ratings.count > 0)

和

> Profile.where('ratings.count > 1').count
   (28.1ms)  SELECT COUNT(*) FROM "profiles" WHERE (ratings.count > 1)
ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR:  missing FROM-clause entry for table "ratings"
LINE 1: SELECT COUNT(*) FROM "profiles" WHERE (ratings.count > 1)
                                               ^
: SELECT COUNT(*) FROM "profiles" WHERE (ratings.count > 1)

注意我的 ratings 模型不包含名为 count 的列。我想要做的是 count 与每个 profile 记录关联的 ratings 对象的数量和 return 具有超过 1 评价关联对象。

如何使用 ActiveRecord 实现？

编辑 1

根据用户 793789 的建议再尝试两个查询：

> Profile.includes(:ratings).where('ratings.count > 1').references(:ratings).count
   (55.3ms)  SELECT COUNT(DISTINCT "profiles"."id") FROM "profiles" LEFT OUTER JOIN "ratings" ON "ratings"."profile_id" = "profiles"."id" WHERE (ratings.count > 1)
ActiveRecord::StatementInvalid: PG::GroupingError: ERROR:  aggregate functions are not allowed in WHERE
LINE 1: ...N "ratings"."profile_id" = "profiles"."id" WHERE (ratings.co...
                                                             ^
: SELECT COUNT(DISTINCT "profiles"."id") FROM "profiles" LEFT OUTER JOIN "ratings" ON "ratings"."profile_id" = "profiles"."id" WHERE (ratings.count > 1)

> Profile.joins(:ratings).where('ratings.count > 1').count
   (40.4ms)  SELECT COUNT(*) FROM "profiles" INNER JOIN "ratings" ON "ratings"."profile_id" = "profiles"."id" WHERE (ratings.count > 1)
ActiveRecord::StatementInvalid: PG::GroupingError: ERROR:  aggregate functions are not allowed in WHERE
LINE 1: ...N "ratings"."profile_id" = "profiles"."id" WHERE (ratings.co...
                                                             ^
: SELECT COUNT(*) FROM "profiles" INNER JOIN "ratings" ON "ratings"."profile_id" = "profiles"."id" WHERE (ratings.count > 1)

Answer 1

Profile.includes(:ratings).where('ratings.count > 0').references(:ratings).count

OP 的编辑 1

几经周折，我们终于定下了这个：

Profile.joins(:ratings).group('profiles.id').having('count(ratings.id) > 0').length

但我觉得必须有更简单的方法来做到这一点。

如何查询关联模型上的对象数量？

How do I query the number of objects on an associated model?

activerecord

ruby-on-rails

active-record-query

ruby-on-rails-5