eager_load
eager_load works with LEFT OUTER JOIN.
Forces eager loading by performing a LEFT OUTER JOIN on args:
User.eager_load(:posts) # SELECT "users"."id" AS t0_r0, "users"."name" AS t0_r1, ... # FROM "users" LEFT OUTER JOIN "posts" ON "posts"."user_id" = # "users"."id"
https://railsdoc.github.io/classes/ActiveRecord/QueryMethods.html#method-i-eager_load
But what about inner join?
eager_load + INNER JOIN
Model
Let’s say you have the following Models.
class Tweet < ApplicationRecord
belongs_to :user
end
class User < ApplicationRecord
has_many :tweets
end
Default eager_load
Tweet.eager_load(:user).to_sql
The output:
SELECT "tweets"."id" AS t0_r0, /*...snip...*/
FROM "tweets"
LEFT OUTER JOIN "users" ON "users"."id" = "tweets"."user_id"
eager_load with INNER JOIN
Add joins before eager_load.
Tweet.joins(:user).eager_load(:user).to_sql
The output:
SELECT "tweets"."id" , /*...snip...*/
FROM "tweets"
INNER JOIN "users" ON "users"."id" = "tweets"."user_id"