Rails activerecord : sum, max and joins

问题:

I have two models users and posts. An user can votes and views a post

#users   id   name  #posts   id   count_votes   count_views   users_id   created_at   updated_at 

I want the user who received the most votes and views on his posts from the last 24 hours. The biggest sum of views and votes win.

WHAT I TRIED I have this SQL query, it's good but I would like to have the user with the max of votes, this one give me all users and I don't know how to add count_views

select u.name as "Name", sum(p.count_votes) from posts p  inner join users u on p.user_id = u.id  where p.created_at >= DATE_SUB(NOW(), INTERVAL 1 day) group by user_id; 

ActiveRecord version

Post.select("users.id, sum(posts.count_votes) as nb_votes") .joins(:user).where("posts.created_at >= ?", 1.day.ago.beginning_of_day) .group("posts.user_id")  # Results on IRB => #<ActiveRecord::Relation [#<Post id: 1>, #<Post id: 3>]>  

How can I combine a sum and a max on these two sums ? Is there a way to have an activerecord code or only raw SQL ?

回答1:

You current query does a grouping on user. So you would get one record for each user in the output. By limiting the output to just 1 record and ordering by votes+views total count, you can get the top user.

Raw SQL:

select u.id, sum(p.count_votes + p.count_views) total from posts p  inner join users u on p.user_id = u.id  where p.created_at >= DATE_SUB(NOW(), INTERVAL 1 day) group by u.id order by total DESC limit 1 ; 

ActiveRecord version: Start from your User model, so you will get the user object in the output instead of Post object, like you have mentioned in the question.

User.select("users.id, sum(posts.count_votes + posts.count_views) as nb_votes") .joins(:post).where("posts.created_at >= ?", 1.day.ago.beginning_of_day) .group("posts.user_id").order("nb_votes DESC").limit(1) 

回答2:

ActiveRecord makes sense once you work with an object, in that case you need to have a User object only, so here is your solution below:

  sql = %Q(SELECT * FROM users    WHERE id = (SELECT users_id FROM posts     WHERE DATE(created_at) = CURDATE()     ORDER BY count_votes DESC, count_views DESC     LIMIT 1   )    LIMIT 1)    ActiveRecord::Base.connection.execute(sql) 

文章来源: Rails activerecord : sum, max and joins