Sql 创建连接到子查询的Rails 3作用域

首先，我是Ruby/Rails的新手，如果这个问题是基本的，我很抱歉

我有一个DB（除其他外）如下所示：

organizations { id, name, current_survey_id }
surveys { id, organization_id }
responses { id, survey_id, question_response_integer }

select * from organizations

select o.id, o.name, cs.average_responses
from organizations o join
(select r.id, avg(r.question_response_integer) as average_responses 
     from responses r 
     group by r.id) cs on cs.id = o.current_survey_id

current_survey_average: lambda do |scope, sort_direction|
  average_answers = Responses.
     select("survey_id, avg(question_response_integer) as average_responses").
     group("survey_id")
  scope.joins(average_answers).order("average_responses #{sort_direction}")
end

我试图创建一个scope方法，将当前调查答案的平均值添加到传入的组织关系中。换句话说，传递到方法中的作用域将生成大致如下所示的SQL：

organizations { id, name, current_survey_id }
surveys { id, organization_id }
responses { id, survey_id, question_response_integer }

select * from organizations

select o.id, o.name, cs.average_responses
from organizations o join
(select r.id, avg(r.question_response_integer) as average_responses 
     from responses r 
     group by r.id) cs on cs.id = o.current_survey_id

current_survey_average: lambda do |scope, sort_direction|
  average_answers = Responses.
     select("survey_id, avg(question_response_integer) as average_responses").
     group("survey_id")
  scope.joins(average_answers).order("average_responses #{sort_direction}")
end

我希望作用域在被lambda处理后生成如下所示的SQL：

organizations { id, name, current_survey_id }
surveys { id, organization_id }
responses { id, survey_id, question_response_integer }

select * from organizations

select o.id, o.name, cs.average_responses
from organizations o join
(select r.id, avg(r.question_response_integer) as average_responses 
     from responses r 
     group by r.id) cs on cs.id = o.current_survey_id

current_survey_average: lambda do |scope, sort_direction|
  average_answers = Responses.
     select("survey_id, avg(question_response_integer) as average_responses").
     group("survey_id")
  scope.joins(average_answers).order("average_responses #{sort_direction}")
end

我得到的最好的东西是这样的：

organizations { id, name, current_survey_id }
surveys { id, organization_id }
responses { id, survey_id, question_response_integer }

select * from organizations

select o.id, o.name, cs.average_responses
from organizations o join
(select r.id, avg(r.question_response_integer) as average_responses 
     from responses r 
     group by r.id) cs on cs.id = o.current_survey_id

current_survey_average: lambda do |scope, sort_direction|
  average_answers = Responses.
     select("survey_id, avg(question_response_integer) as average_responses").
     group("survey_id")
  scope.joins(average_answers).order("average_responses #{sort_direction}")
end

这基本上只是一个暗中操作——除其他事项外，它没有指定如何将作用域连接到

average\u answers

——但我还没有找到任何关于如何进行这种连接的文档，我已经没有什么可以尝试的了

有什么建议吗

编辑：谢谢肖恩·希尔的回答。为了记录在案，以下是我最终使用的代码：

current_survey_average: lambda do |scope, sort_direction|
  scope_table = scope.arel.froms.first.name
  query = <<-QUERY
    inner join (
     select r.survey_id, avg(r.question_response_integer) as average_responses
      from responses r
      group by r.survey_id
    ) cs
    on cs.survey_id = #{scope_table}.current_survey_id
  QUERY
  scope.
    joins(query).
    order("cs.average_responses #{sort_direction}")
end

当前调查平均值：lambda do范围、排序方向|
scope\u table=scope.arel.froms.first.name
query=我还不能测试这个，但是我认为下面的方法可以正常工作，或者稍微调整一下

class Response < ActiveRecord::Base
  scope :averaged, -> { select('r.id, avg(r.question_response_integer) as average_responses').group('r.id') }

  scope :current_survey_average, ->(incoming_scope, sort_direction) do
    scope_table = incoming_scope.arel.froms.first.name
    query = <<-QUERY
      INNER JOIN ( #{Arel.sql(averaged.to_sql)} ) cs
      ON cs.id = #{scope_table}.current_survey_id
    QUERY

    incoming_scope.joins(query).order("average_responses #{sort_direction}")
  end
end

类响应{select（'r.id，avg（r.question\u response\u integer）作为平均\u responses'）。group（'r.id'）}
范围：当前调查平均值，->（传入范围、排序方向）do
scope\u table=传入的\u scope.arel.froms.first.name
query=我还不能测试这个，但是我认为下面的方法可以正常工作，或者稍微调整一下

class Response < ActiveRecord::Base
  scope :averaged, -> { select('r.id, avg(r.question_response_integer) as average_responses').group('r.id') }

  scope :current_survey_average, ->(incoming_scope, sort_direction) do
    scope_table = incoming_scope.arel.froms.first.name
    query = <<-QUERY
      INNER JOIN ( #{Arel.sql(averaged.to_sql)} ) cs
      ON cs.id = #{scope_table}.current_survey_id
    QUERY

    incoming_scope.joins(query).order("average_responses #{sort_direction}")
  end
end

类响应{select（'r.id，avg（r.question\u response\u integer）作为平均\u responses'）。group（'r.id'）}
范围：当前调查平均值，->（传入范围、排序方向）do
scope\u table=传入的\u scope.arel.froms.first.name
非常感谢，这就是答案。我在上面发布了我的修改版本：非常感谢。非常感谢，这就是答案。我在上面发布了我的修改版本：非常感谢。