在has_many上按计数排序：through

Question

我使用Rails4。我有一个与我有多对多关系的应用程序：

class User < ActiveRecord::Base
  has_many :relationshipfollows, :foreign_key => "follower_id",
                           :dependent => :destroy
  has_many :following, :through => :relationshipfollows, :source => :followed
end

class Project < ActiveRecord::Base
 has_many :relationshipfollows, :foreign_key => "followed_id",
                           :dependent => :destroy
 has_many :followers, :through => :relationshipfollows, :source => :follower
end

class Relationshipfollow < ActiveRecord::Base
  belongs_to :follower, :class_name => "User"
  belongs_to :followed, :class_name => "Project"
end

我遵循此教程： http : //ruby.railstutorial.org/chapters/following-users? version= 3.0#top

但是现在，我想按关注者的数量列出所有已订购的项目。 像这样 ：

1. project1 | 99 followers
2. project2 | 16 followers
3. project3 | 2 followers
...

我是Rails的新手，我想我一直在犯一个错误，因为我尝试了很多这样的示例： Rails 3 has_many：through或has_many 上的Count by Count ，通过：关系计数

我尝试这种方法： Project.joins(:relationshipfollows).group("relationshipfollows.project_id").order("count(relationshipfollows.project_id) desc")

但是我有这个错误： SQLite3::SQLException: no such column: relationshipfollows.project_id: SELECT "projects".* FROM "projects" INNER JOIN "relationshipfollows" ON "relationshipfollows"."followed_id" = "projects"."id" GROUP BY relationshipfollows.project_id ORDER BY count(relationshipfollows.project_id) desc

我尝试另一种方法：

Project.joins(:relationshipfollow).select('following.*, COUNT(followers.id) AS user_count').group('project_id').order('COUNT(followers.id) DESC')

但是我有这个错误： Association named 'relationshipfollow' was not found on Project; perhaps you misspelled it? Association named 'relationshipfollow' was not found on Project; perhaps you misspelled it?

有人可以帮我找到正确的方向，如何使其全部正常工作吗？

亲切地

编辑：我认为问题是从这里开始。 当我尝试这个：

Relationshipfollow.select(:followed_id, "COUNT(follower_id) AS total").group(:followed_id).order("total DESC")

他把这个还给我：

=>＃ActiveRecord :: Relation [＃Relationshipfollow id：无，followed_id：2，＃Relationshipfollow id：无，followed_id：1，＃Relationshipfollow id：无，followed_id：3]

所有项目都按照关注者的数量排序，并且相对于我的测试，所有followed_id（项目）的顺序都很好。 但是当我像这样将其加入到我的模型项目中时：

Project.joins(:relationshipfollows).select(:followed_id, "COUNT(follower_id) AS total").group(:followed_id).order("total DESC")

他给我返回了一个项目列表，但是project_id为NULL：

=> #ActiveRecord::Relation [# Project id: nil, # Project id: nil, # Project id: nil]

Answer 1

这就是我要做的：

#app/models/project.rb
Class Project < ActiveRecord::Base
     has_many :relationshipfollows, :foreign_key => "follower_id", :dependent => :destroy
     has_many :followers, :through => :relationshipfollows, :source => :follower

     scope :sort_by_followers, -> { joins(:followers).select("followers.*", "COUNT(followers.id) AS follower_count").group(:project_id).order("follower_count DESC") }
end

#app/controllers/projects_controller.rb
def index
    @projects = Project.sort_by_followers
end

#app/views/projects/index.html.erb
<ol>
    <% @projects.each_with_index do |project, i| %>
        <li><%= "Project#{i} | #{project.follower_count} followers" %></li>
    <% end %>
</ol>

Answer 2

Project.joins（：relationshipfollows）将进行内部联接。 因此，没有关注者的项目将不包括在结果集中。 您需要这样的东西：

Project.select("projects.*, COUNT(relationshipfollows.follower_id) as follower_count").joins("LEFT OUTER JOIN relationshipfollows ON relationshipfollows.followed_id = projects.id").group("projects.id").order("follower_count DESC")

Answer 3

我的救援方案是在我的Project模型中添加一个整数numberfollowers

但是在另一个项目和Rails指南（ http://guides.rubyonrails.org/active_record_querying.html ）中，我终于找到了我的请求的答案

Project.joins(:relationshipfollows).select('projects.*, COUNT(followed_id) as user_count').group('projects.id').order('user_count DESC')