ruby-on-rails - Ruby复杂查询优雅解决方案

Question

在我的 Rails 4 项目中，我有以下表格

在此SO question ，我搜索了一个 SQL 查询以获取具有实际项目状态 id = XX 的项目。实际上，我指的是具有 max(created_at) 的那个。

我的查询得到了答案

select p.* from projects p
     left join projects_status_projects psp on (psp.project_id = p.id)
     where created_at = (select max(created_at) from projects_status_projects 
           where project_id = p.id)    
     and project_status_id = XX

我的模型已定义

class Project < ActiveRecord::Base
   has_many :projects_status_projects
   has_many :projects_statuses, :through => :projects_status_projects
end

class ProjectStatus < ActiveRecord::Base
   has_many :projects_status_projects
   has_many :projects, :through => :projects_status_projects
end

class ProjectsStatusType < ActiveRecord::Base
   belongs_to :project
   belongs_to :project_status
end

在我的 Project 模型中，我有以下方法

def self.with_status(status)
   joins(:projects_status_projects)
       .where('projects_status_projects.created_at = (select max(created_at) from 
                    projects_status_projects where project_id = p.id)')
       .where('projects_status_projects.project_status_id = ?', status)
end

虽然查询是正确的，但接收到的结果被很好地过滤了，我觉得这个解决方案很糟糕，一点也不优雅。

有什么方法可以用范围获得相同的结果吗？

感谢您的帮助。

Answer 1

你觉得怎么样

scope :with_status, -> (status) { 
   ProjectsStatusType.where(:project_status_id, status).order(:created_at).last.project 
}

根据评论编辑:

正如 sockmonk 所说，范围应该是可链接的。这是一种更简洁的方法，如果找不到项目，它也可以解决问题。

# ProjectStatusType model
scope :with_ordered_status, -> (status) { 
   where(:project_status_id, status).order(:created_at)
}

# Project model
def self.find_by_status(status)
  project_statuses = ProjectsStatusType.with_ordered_status(status)
  project_statuses.any? ? project_statuses.last.project : nil
end