July 3rd, 2008 by
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
@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| -%>
- <%= f.check_box :language_ids, {:checked => user_speaks_language?(language)}, “#{language.id}”, “” -%> <%= "#{language.english_name}" -%>
<% end -%>
And we’ll need this helper method:
def user_speaks_language?(language)
if @user && !@user.login.nil? # 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
