Question

This is in continuation to the question which was raised here

How to add one-to-many objects to the parent object using ActiveRecord

class Foo < ActiveRecord::Base
  has_many :foo_bars
end

class Bar < ActiveRecord::Base
end  

class FooBar < ActiveRecord::Base
  belongs_to :foo
  belongs_to :bar
end 

How to handle removal of entries in a multi select check box are used to represent one-to-many entities. I am able to add or update entries, but removal seems to fail since foo_id seems to be empty and the query seems to be updating instead of delete.

EDIT :

I tried with @charlysisto suggestion using the following code

My Controller code is as follows :

  class Foo < ActiveRecord::Base
    has_many :foo_bars
    has_many :bars, :through => :foo_bars
  end

   def edit
    @foo = Foo.find(params[:id])
    @sites = Site.where(company_id: @current_user.company_id).all
   end

  def update
    @foo = Foo.find(params[:id])

    if @foo.update_attributes(params[:foo])
      flash[:notice] = "Foo was successfully updated"
      redirect_to foos_path
    else
      render :action => 'edit'
    end
   end

View code is as follows :

<% @bars.each do |bar| %>
    <%= check_box_tag 'bar_ids[]', bar.id %>
    <%= bar.name %>
<% end %>

So I tried with these changes, but still foo_bars doesn’t seem to reflect the changes if I removed a record.

Answer 1

What’s missing in your associations is this :

class Foo < ActiveRecord::Base
  has_many :bars, :through => :foo_bars
end

… the has_many (or has_many :through) macro gives you a truck load of methods including bar_ids and bar_ids= [...]

So all you need to do in your views/controller is :

# edit.html.haml which will send an array of bar_ids
=f.select :bar_ids, Bar.all.map {|b| [b.name, b.id]}, {}, :multiple => true

# foo_controller
@foo.update_attributes(params[:foo])

And that’s it! No need to manually set or delete the associations in FooController#update…