Rails Format Collection_Select Based on two relationships

Question

I'm trying to figure out how to construct a collection_select to include two relationships. Here are my models:

class Country < ActiveRecord::Base
  has_many :companies, :dependent => :destroy
end

class Company < ActiveRecord::Base
  belongs_to :country
  has_many :departments, :dependent => :destroy
end

class Department < ActiveRecord::Base
  belongs_to :company
end

When I create a new company I use the following to show a select box based on the relationship.

<%= collection_select(:company, :country_id, Countries.all, :id, :name, :prompt => 'Please select country') %>

But for the departments I'd like to have a select which let's the user select it's company from a select which also includes the companies country, formatted in the following way:

Company 1 - Country 1 Company 2 - Country 1

If i use the following I will only get a list of all the companies which I'd like to be able to see from the list which country they are from.

<%= collection_select(:device, :cabinet_id, Cabinet.all, :id, :name, :prompt => 'Please select cabinet') %>

Is there a way for rails to pull the information for the country into a select and append the entry with it's parent country?

I hope I've worded this question correctly! Sorry if it isn't clear.

Answer 1

Use

UPDATE: move logic code to model

# company.rb
def company_with_country
  "#{name} - #{country.name}" # this is better than using `string + string` since it creates only 1 string
end

# view
collection_select :department, :company_id, Company.includes(:country).all, :id, :company_with_country

UPDATE: faster version because it only uses needed columns

# controller
@companies = Company.joins(:country)
  .select('companies.id, companies.name, countries.name AS country_name')
  .map { |c| ["#{c.name} - #{c.country_name}", c.id] }`

# view
select :department, :company_id, @companies