Rails join table: Ultimate tutorial

This is a complete tutorial for creating join table in Ruby on Rails. It will show you how to generate the model, address associations and join table model. Also, it will show you how to write a form with multiple select boxes and how to handle it in the controller.

First, let's create join table in Rails way, with the city and the cleaner as references.

rails g model Assignment city:references cleaner:references

This will create the migration:

create_assignments.rb
class CreateAssignments < ActiveRecord::Migration
def change
create_table :assignments do |t|
t.references :city, index: true, foreign_key: true
t.references :cleaner, index: true, foreign_key: true
t.timestamps null: false
end
end
end

cleaner.rb

class Cleaner < ActiveRecord::Base
has_many :assignments
has_many :cities, through: :assignments
end

city.rb

class City < ActiveRecord::Base
has_many :assignments
has_many :cleaners, :through => :assignments
end

assignment.rb

class Assignment < ActiveRecord::Base
belongs_to :city
belongs_to :cleaner
end

cleaners_controller.rb

`private

def cleaner_params
params.require(:cleaner).permit(city_ids: [])
end`

_form.html.erb Select multiple form

<%= form_for(@cleaner) do |f| %>
<p>
<%= f.label :cities %><br />
<% for city in City.all %>
<%= check_box_tag "cleaner[city_ids][]", city.id, @cleaner.cities.include?(city) %>
<%=h city.name %><br />
<% end %>
</p>
<div class="actions">
<%= f.submit %>
</div>
<% end %>

Hope you find this tutorial helpful!

Originally posted at kolosek.com.