Question

I have this schema:

• There is a table for persons.
• Each person has one “info” table.
• Persons can have friends. This is stored in another table called “friends”, which has a foreign key for the person, and another one for his friend (both are pointing to the “person” table).

“person” model:

class Person < ActiveRecord::Base
  has_one :info
  has_many :friends
end

“info” model:

class Info < ActiveRecord::Base
  belongs_to :person

  attr_accessible :description
end

“friends” model:

class Friend < ActiveRecord::Base
  belongs_to :person

  attr_accessible :friend_id
end

Let’s suppose we have 2 persons: person1 and person2. Each one with a record in the “info” table storing its description. And let’s suppose that person2 is a friend of person1.

content of “person” table:

id: 1

id: 2

content of “info” table:

id: 1, person_id: 1, description: “This is person 1, our main dude.”

id: 2, person_id: 2, description: “This is person 2, our secondary dude.”

content of “friends” table:

id: 1, person_id: 1, friend_id: 2

If I want to get person1’s friends I do this:

Person.first.friends

This will give me:

id: 1, person_id: 1, friend_id: 2

Now, how do I add the “info” content for each row?

Answer 1

Here is the first solution I have come with:

Friends.select("p.description").joins("INNER JOIN info i ON i.person_id = friend_id").where(person_id: 1)

Anyone with a better/clearer/more efficient one?