帮助处理具有太多联接的复杂 ActiveRecord 查询

Question

我有以下模型

class User < ActiveRecord::Base
  has_many :occupations,     :dependent => :destroy
  has_many :submitted_jobs,  :class_name => 'Job', :foreign_key => 'customer_id'
  has_many :assigned_jobs,   :class_name => 'Job', :foreign_key => 'employee_id'
end

class Job < ActiveRecord::Base
  belongs_to :customer, :class_name => 'User', :foreign_key => 'customer_id'
  belongs_to :employee, :class_name => 'User', :foreign_key => 'employee_id'
  belongs_to :field
end

class Occupation < ActiveRecord::Base
  belongs_to :user
  belongs_to :field
  belongs_to :expertise
end

以及 Field （仅名称和 id）和 Expertise （名称和整数排名）。

我需要创建一个过滤器，其工作原理类似于以下伪代码。

select * from jobs where employee_id == current_user_id
or employee_id == 0
  and current_user has occupation where occupation.field == job.field
  and if job.customer has occupation where occupation.field == job.field
    current_user.occupations must include an occupation where field == job.field
      and expertise.rank > job.customer.occupation.expertise.rank

您可以看到我如何通过如此复杂的查询快速耗尽我的 SQL 知识。

你会怎么做？正确的 SQL 会很棒，但是如果 Rails 人员可以向我指出使用 ActiveRecord 方法执行此操作的正确方法，那也很棒。或者也许我没有很好地构建我的模型；我愿意接受各种建议。

谢谢！

Answer 1

我可能错过了一些东西，并且没有考虑重构模型，但这里有一些东西可能会帮助您获得完整的解决方案或如何重新制定查询

代码未经测试或语法检查

@jobs = Job.
    joins(:employee,:occupation).
    includes(:customer => {:occupations => :expertise}).
    where(:employee_id => current_user.id).
    where("occupations.field_id = jobs.field_id").all

user_occupations = current_user.occupations.include(:expertise)

user_occupations_by_field_id = user_occupations.inject({}) do |hash,oc|
    hash[oc.field_id] = oc
    hash
end

@jobs.reject! do |j|
  common_occupations = j.customer.occupations.select do |oc|
    if c = user_occupations_by_field_id[oc.field_id]
        !user_occupations.select do |eoc|
            c.field_id == eoc.field_id && c.expertise.rank > oc.expertise.rank
        end.empty?
    else
        true
    end
  end

end