Multiple Checkboxes with HABTM

Has and Belongs to Many with Multiple Check boxes

So if you are trying to do a multiple select of checkboxes and using habtm in your project, but when you submit the form, only one value was available in your controller. While you try to edit records in database but because of some error you get back to the pre field form and you found that the checkboxes checked by you gone ,then here’s the solution

Model:

   class Customer < ActiveRecord::Base
     has_and_belongs_to_many :intrests
   end

Controller code:

    class CustomersController < ApplicationController
      def create
        if request.post?
           @customer=Customer.new(params[:customer])
           @customer.save
        end
      end

      def edit
       @customer=Customer.find_by_id(params[:id]) if params[:id]
       if @customer
        if request.post?
         if @customer.update_attributes(customer)
           flash.now[:message]="Update successfully "
         end
        end
       else
        flash[:message]="Page requested by you does not exists"
       end
      end
    end

Your View:

   <% form_for :customer,  do |f| -%>
     First Name:
      <%= f.text_field :first_name  -%>
     Last Name:
      <%= f.text_field :last_name -%>
     <% for intr in total_intrests -%>
      <%= check_box_tag "customer[interest_ids][]","#{intr.id}",
          interest(intr) -%> # interest is a helper method  
      <%= "#{intr.name}" -%>
     <% end -%>
   <% end -%>

helper method
  def interest(i)
    if @customer
      @customer.interests.include?(i)
    else
      false
    end
  end

View generate a checkbox for every interest(all_interest=Interest.find(:all)). The name of the input is significant obviously. The trailing “[]” on the name means the end result will be the list of checked ids. This list will be stored on the @params['customer'] hash with the key ‘interest_ids’. When the controller calls @customer.update_attributes(@params[:customer]), it tries to call @customer.key= for each of the keys on @params[:customer]. What’s important to realize is that these keys don’t have to actually be attributes on the Customer model. All that’s important is that there’s a key= method on the model. Model automatically contains a “collection_ids=” method for habtm and has-many associations.

This method will load the objects identified by the ids and call the “interest=(list)” method on the model with the freshly loaded list. This method in turn, will compare the list to the current list of interests and delete/add interests as necessary.