如何为 ActiveRecord 连接应用附加条件

Question

假设我尝试计算一段时间内每个部门的事故数量。所以我有2张桌子。我正在尝试使用 ActiveRecord 来获取答案，它看起来像这样

class Division < ApplicationRecord
  has_many :accidents

end

class Accident < ApplicationRecord
  belongs_to :division

end


Division.left_joins(:accidents).where('accidents.occurred_at > ?', Time.now - 1.year).group(:name).count

在本例中 ActiveRecord 生成此 SQL

SELECT COUNT(accidents.id) AS "count_all", "divisions"."name" AS "divisions_name"
FROM "divisions"
LEFT OUTER JOIN "accidents" ON "accidents"."division_id" = "divisions"."id"
WHERE (accidents.occurred_at > '2022-07-30 20:56:10.178153')
GROUP BY "divisions"."name"

这里的问题是，如果某些除法的事故计数为0，我们将不会在查询结果中看到它，所以我需要像这样的SQL

SELECT COUNT(accidents.id) AS "count_all", "divisions"."name" AS "divisions_name"
FROM "divisions"
LEFT OUTER JOIN "accidents" ON "accidents"."division_id" = "divisions"."id" and accidents.occurred_at > '2022-07-30 20:56:10.178153'
GROUP BY "divisions"."name"

是否可以指定一些额外的加入条件？ 我知道我们可以为 has_many 关系指定附加条件，但这将是静态条件。我希望它根据用户请求参数是动态的

我试图避免使用原始sql作为连接条件e.q.

Division.joins("LEFT OUTER JOIN accidents ON accidents.division_id = divisions.id
and (accidents.occurred_at > '2022-07-30 20:56:10.178153'").group(:name).count('accidents.id')

Answer 1

我会尝试像这样的与范围的关联

# in the model
class Division < ApplicationRecord
  has_many :accidents
  has_many :recent_accidents, class_name:  'Accident', 
                              foreign_key: 'division_id',
                              -> { where occurred_at: (1.year.ago..) }

并且会像这样使用它：

Division.left_outer_joins(:recent_accidents)
        .group(:name)
        .count('accidents.id')

Answer 2

使用范围和

JOIN

 来简化最终查询怎么样？

class Division < ApplicationRecord
  scope :with_accidents_from, ->(occurred_at) do
    joins_query =
      sanitize_sql([
        'LEFT OUTER JOIN accidents ON accidents.division_id = divisions.id AND accidents.occurred_at > ?',
        occurred_at
      ])

    joins(joins_query)
  end
end

然后

Division.with_accidents_from(1.year.ago).group(:name).count('accidents.id')