Checkbox list in Ruby on Rails using HABTM

Checkboxes are one of those things that look easy and should be easy, but they aren't always easy. I needed a solution that could create a checkbox list of languages that a user speaks. So I don't forget here's how to do it:

The migrations are important. You have to be sure to exclude the id parameter when you create languages_users or you will get ' Mysql::Error: #23000Duplicate entry' due to the fact that ActiveRecord will try to store a value in the id field that indicates which model created the entry (User.languages << vs Langauges.users). The other option is the create the id parameter so that the direction is maintained but be sure that it is not created as a primary key.


class LanguagesUsers < ActiveRecord::Migration
    def self.up
        create_table :languages_users, :id => false, :force => true do |t|
            t.integer :user_id
            t.integer :language_id
            t.timestamps
        end
    end

def self.down
    drop_table :languages_users
end

end


class Languages < ActiveRecord::Migration

def self.up
    create_table "languages", :force => true do |t|
        t.string  "name"
        t.string  "english_name"
        t.integer "is_default", :default => 0
    end
end

def self.down
    drop_table "languages"
    drop_table "users_languages"
end

end


class Users < ActiveRecord::Migration

def self.up
    create_table "users", :force => true do |t|
        t.string  "login"
        # other fields excluded for brevity
    end
end

def self.down
    drop_table "users"
end

end

Here are my models: user.rb


class User < ActiveRecord::Base
    has_and_belongs_to_many :languages
end

language.rb:


class Language < ActiveRecord::Base
  has_and_belongs_to_many :users
end

In my user_controller.rb the create and update methods are simple. This is thanks to the fact that you get a language_ids method on the user object because of the HABTM relationship.


    def create
        @user = User.new(params[:user])
        @user.save
    end

def update
    params[:user][:language_ids] ||= []

    @user = User.find(current_user)

    if @user.update_attributes params[:user]
        flash[:notice] = "Settings have been saved."
        redirect_to edit_user_url(@user)
    else
        flash.now[:error] = @user.errors
        setup_form_values
        respond_to do |format|
            format.html { render :action => :edit}
        end
    end

end

On to the view:

    <% @languages.each do |language| -%>

  • <%= check_box_tag "user[language_ids][]", language.id, user_speaks_language?(language) -%> <%= language.english_name -%>
  • <% end -%>

    NOTE: I had an error in my original method. This code:

  • <%= f.check_box :language_ids, {:checked => user_speaks_language?(language)}, "#{language.id}", "" -%> <%= "#{language.english_name}" -%>
  • should be this:

  • <%= check_box_tag "user[language_ids][]", language.id, user_speaks_language?(language) -%> <%= language.english_name -%>
  • And we'll need this helper method:

    
    def user_speaks_language?(language)
        if @user && [email protected]? # no sense in testing new users that have no languages
            @user.languages.include?(language)
        else
            false
        end
    end
    

    The result is that you will get a list of check boxes that update values in the join table that is part of the has_and_belongs_to_many relationship. Rails is very cool