LEFT OUTER joins in Rails 3

Question

I have the following code:

@posts = Post.joins(:user).joins(:blog).select

which is meant to find all posts and return them and the associat

Answer 1

Good news, Rails 5 now supports LEFT OUTER JOIN. Your query would now look like:

@posts = Post.left_outer_joins(:user, :blog)

Answer 2

Use eager_load:

@posts = Post.eager_load(:user)

Answer 3

You can do with this with includes as documented in the Rails guide:

Post.includes(:comments).where(comments: {visible: true})

Results in:

SELECT "posts"."id" AS t0_r0, ...
       "comments"."updated_at" AS t1_r5
FROM "posts" LEFT OUTER JOIN "comments" ON "comments"."post_id" = "posts"."id"
WHERE (comments.visible = 1)

Answer 4

class User < ActiveRecord::Base
     has_many :friends, :foreign_key=>"u_from",:class_name=>"Friend"
end

class Friend < ActiveRecord::Base
     belongs_to :user
end


friends = user.friends.where(:u_req_status=>2).joins("LEFT OUTER JOIN users ON users.u_id = friends.u_to").select("friend_id,u_from,u_to,u_first_name,u_last_name,u_email,u_fbid,u_twtid,u_picture_url,u_quote")

Answer 5

I'm a big fan of the squeel gem:

Post.joins{user.outer}.joins{blog}

It supports both inner and outer joins, as well as the ability to specify a class/type for polymorphic belongs_to relationships.

Answer 6

@posts = Post.joins("LEFT OUTER JOIN users ON users.id = posts.user_id").
              joins(:blog).select