gistfile1.rb

# Simple JOIN
User.joins(:account)  # User -> Account
# Will produce
# SELECT `users`.* FROM `users` INNER JOIN `accounts` ON `accounts`.`user_id` = `users`.`id`

# Complicated JOIN
Trait.joins(:user => :account)  # Trait -> User -> Account
# Will produce
# SELECT `traits`.* FROM `traits` INNER JOIN `users` ON `users`.`id` = `traits`.`user_id` INNER JOIN `accounts` ON `accounts`.`user_id` = `users`.`id`

# And more complicated JOIN
Completion.joins(:trait => {:user => :account}) # Completion -> Trait -> User -> Account
# Will produce
# SELECT `completions`.* FROM `completions` INNER JOIN `traits` ON `traits`.`id` = `completions`.`trait_id` INNER JOIN `users` ON `users`.`id` = `traits`.`user_id` INNER JOIN `accounts` ON `accounts`.`user_id` = `users`.`id`