Takehiro Adachi

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09 Oct 2012
nested object forms with checkbox

versions: rails 3.2.8, ruby 1.9.4

Rails is an awesome framework.
You can really concentrate on what you want you make, not how to make it.
One good example is nested object forms.
You dont have to write tons of code in your controller to operate models which has relations like has_many.

There’s an good tutorial in railscast.com, #196 Nested Model Form Part 1 and #197 Nested Model Form Part 2, so I’m not gonna explain about nested object forms.

I wanted to create an nested object forms using checkboxes just like the below image.


This needs a little twist, if you understand the nested object forms you’ll know why.

I’ll show you how I did this, if there’s any better way to do this, please comment :)

Lets say we have article table and category table, And we want to register multiply category on 1 article by using checkboxes.

The basics(models)

the models will be like the below

class Article < ActiveRecord::Base
  attr_accessible :articles_categories_attributes

  has_many :categories, :through => :articles_categories
  has_many :articles_categories, :dependent => :destroy

  accepts_nested_attributes_for :articles_categories, :allow_destroy => true
class ArticlesCategory < ActiveRecord::Base
  attr_accessible :article_id, :category_id

  belongs_to :article
  belongs_to :category
class Category < ActiveRecord::Base
  attr_accessible :name

  has_many :articles, :through => :articles_categories
  has_many :articles_categories, :dependent => :destroy

form and update method

this is the part which is different from normal nested object forms


<% Category.all.each do |category| %>

  <% check_flag = @article.articles_categories.any? { |articles_category| articles_category.category_id == category.id } %>

  <%= check_box_tag "article[articles_categories_attributes][][category_id]", category.id, check_flag %>
  <%= category.name %>
<% end %>

basically you can’t use fields_for, so you have to write it like this.

update method

def update
  ArticlesCategory.transaction do
    @article = Article.find(params[:id], :lock => true)
    flash[:notice] = 'Article was successfully updated.'
    redirect_to :action => 'index'
  rescue ActiveRecord::RecordInvalid
    render :action => 'edit'

If we don’t do this, the checkbox which has been turned off wont be deleted properly.

That’s it! feel free to comment.

Takehiro Adachi at 00:00

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