Order By Count on has_many :through

问题

I use Rails 4. I have an application where i have a many-to-many relationship :

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

I follow this tutorial : http://ruby.railstutorial.org/chapters/following-users?version=3.0#top

But now I'd like to list all projects ordered by the number of follower. Like this :

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

I'm new to rails and I guess I keep making a mistake because I try a lot of examples like this : Rails 3 Order By Count on has_many :through or has_many , through: relationship count

I try this method : Project.joins(:relationshipfollows).group("relationshipfollows.project_id").order("count(relationshipfollows.project_id) desc")

But i have this error : 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

And I try a another method :

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

But I have this error : Association named 'relationshipfollow' was not found on Project; perhaps you misspelled it?

Could someone please help me to find the right direction how to make it all work ?

Cordially

Edit : I think the problem its from here. When I try this :

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

he return me this :

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

All projects are ordered by the number of followers and all followed_id (projects) are in the good order in relative of my test. But when I join this to my model Project like this :

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

he return me a list of projects but with project_id NULL :

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

回答1:

Here's what I would do:

#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>

回答2:

Project.joins(:relationshipfollows) will do an inner join. So, Projects without followers will NOT be included in the result set. You need something like this:

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")

回答3:

My rescues solution was to add a integer numberfollowers in my Project model

But with another project and the rails guides (http://guides.rubyonrails.org/active_record_querying.html), I finally found the answer to my request

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

来源：https://stackoverflow.com/questions/22703820/order-by-count-on-has-many-through

标签

sql

ruby-on-rails

ruby

count

has-many-through