On Tuesday, 26 August 2014 09:10:23 UTC-4, Ganesh Ranganathan wrote: > > Hi, > > Is it possible to do a left outer join in Rails4. This is my model and I > am trying to write a scope which will do a left outer join of users with > the message, comments and likes tables and then group by id to get total > count. > > So the final result set would be cuuser.*, message_count, likes_count and > comments_count. Any idea how this can be accomplished? Thanks in Advance! > > class Cuuser < ActiveRecord::Base > has_and_belongs_to_many :groups > has_many :messages > has_many :comments > has_many :likes > > validates :username, format: { without: /\s/ } > scope :superusers, -> { joins(:comments, :likes). > select('cuusers.id'). > group('cuusers.id'). > having('count(comments.id) + count(likes.id) > 2')} > > Couple thoughts:
* plain `joins` is going to do an INNER JOIN. You might want something like this: includes(:comments, :likes).references(:comments, :likes).select('cuusers.id').group('cuusers.id').having(...) * BUT: that query is going to be fairly inefficient, since it's going to have to compute *every* group before filtering them with HAVING. Instead, you might want to do this bookkeeping differently by using the built-in counter caching mechanism. More info here: http://guides.rubyonrails.org/association_basics.html#counter-cache Using counter caches in your example will mean adding a `comments_count` and `likes_count` column to your cuusers table. Then your scope could just use `where` to compare them... --Matt Jones -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To unsubscribe from this group and stop receiving emails from it, send an email to rubyonrails-talk+unsubscr...@googlegroups.com. To post to this group, send email to rubyonrails-talk@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/rubyonrails-talk/5a9a57b8-3a9d-48fd-9435-418355f7ec32%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.