Rails associations nesting

Question

I have three tables that are created by a non rails application. The following models are just the associations for the tables.

class Client < ActiveRecord::Base
  has_many :programs
  has_many :locations, :through => :programs
end

class Program < ActiveRecord::Base
  belongs_to :location
  belongs_to :client
end

class Location < ActiveRecord::Base
  has_many :programs
  has_many :clients, :through => :programs
end

I would like a simpler way to list out all the programs by location for a client.

I thought the following code would work, but it returns all programs for that location, and that completely makes sense.

@client.locations.each do |location|
  <h2>location.name</h2>
  <ul>
   location.programs.each do |program|
   <li>program.name</li>
  end
  </ul>
end

I'm currently using

@client.locations.each do |location|
      <h2>location.name</h2>
      <ul>
       Program.where(:location_id => location.id, :client_id => @client.id).each do |program|
       <li>program.name</li>
      end
      </ul>
    end

But this is against MVC principals and is ugly.

I'm not sure how to write this code elegantly, and would appreciate input.

Answer 1

You can use includes method for eager loading the data. Also, using include for this situation will create a join query that will fetch only those programs which are related to both location and client.

@client.locations.includes(:programs).each do |location|
  <h2>location.name</h2>
  <ul>
    location.programs.each do |program|
      <li>program.name</li>
    end
  </ul>
end

Though you should avoid using database queries in view files. So you can move @locations = @client.locations.includes(:programs) to your controller action and use @locations in view to maintain the structure.

Answer 2

You can do this

@client.programs.each do |program|
  <h2>program.location.name</h2>
  <ul>
      <li>program.name</li>
    end
  </ul>
end