Rails eager_load
Rails eager_load works with LEFT OUTER JOIN query.
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"
ActiveRecord::QueryMethods eager_load | RailsDoc(β)
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 SQL:
SELECT "tweets"."id" AS t0_r0, /*...snip...*/
FROM "tweets"
LEFT OUTER JOIN "users" ON "users"."id" = "tweets"."user_id"
LEFT OUTER JOIN is used.
eager_load with INNER JOIN
Add joins before eager_load.
Tweet.joins(:user).eager_load(:user).to_sql
The SQL:
SELECT "tweets"."id" , /*...snip...*/
FROM "tweets"
INNER JOIN "users" ON "users"."id" = "tweets"."user_id"
INNER JOIN is used.