Ruby on Rails Model with table join

Question

In my database, I create three tables which are user, user_group, user_group_info.
I want to do something like this query, but i have no idea how can i join the two tables.

SELECT * FROM user AS u
INNER JOIN user_group AS ug ON u.user_group_id=ug.user_group_id
INNER JOIN user_group_info AS ugi ON ug.user_group_id=ugi.user_group_id
WHERE ugi.language_id = 1

User Model

class User < ApplicationRecord
    self.table_name = "user"
    self.primary_key = "user_id"
    belongs_to :user_group
end

---

UserGroup Model

 class UserGroup < ApplicationRecord self.table_name = "user_group" self.primary_key = "user_group_id" has_many :user belongs_to :user_group_info end 

---

UserGroupInfo Model

 class UserGroupInfo < ApplicationRecord self.table_name = "user_group_info" has_many :user_group end 

Answer 1

You can use ActiveRecord to create your query rather than creating it by hand. Try this:

User.joins(user_group: :user_group_info).where(user_group_infos: { language_id: 1 })

This should translate into what you gave as an example query in your question.

You start with User and you join with user_groups . Through user_groups , you join with user_group_infos . Finally, you add a condition on the user_group_infos . There are a couple ways to write that.

where("user_group_infos.language_id = ?", language_id)
# or
where(user_group_infos: { language_id: language_id })