Question

I’m using simple_form, and I just want to create association between categories and articles using categorization table.

But I have this error:
Can’t mass-assign protected attributes: category_ids.
app/controllers/articles_controller.rb:36:in `update’

articles_controller.rb

def update
    @article = Article.find(params[:id])
      if @article.update_attributes(params[:article]) ---line with the problem
        flash[:success] = "Статья обновлена"
        redirect_to @article
      else
        render :edit
      end
end

article.rb

has_many :categorizations
has_many :categories, through: :categorizations

category.rb

has_many :categorizations
has_many :articles, through: :categorizations

categorization.rb

belongs_to :article
belongs_to :category

categorization has article_id and category_id fields.

My _form.html.erb

<%= simple_form_for @article, html: { class: "form-horizontal", multipart: true } do |f| %>
  <%= f.error_notification %> 
  <%= f.input :title %>
  <%= f.association :categories %>
  <%= f.input :teaser %>
  <%= f.input :body %>
  <%= f.input :published %>
 <% if @article.published? %>
   <%= f.button :submit, value: "Внести изменения" %>
 <% else %>
   <%= f.button :submit, value: "Опубликовать" %>
  <% end %>
<% end %>

Answer 1

do you have attr_accessible in article.rb?

if so add

     attr_accessible :title, :category_ids

Also make sure you really want this for all forms… If not add this:

  attr_accessible :title, :category_ids, :as => :admin

then

@article = Article.new
@article.assign_attributes({ :category_ids => [1,2], :title => 'hello' })
@article.category_ids # => []
@article.title # => 'hello'

@article.assign_attributes({ :category_ids => [1,2], :title => 'hello' }, :as => :admin)
@article.category_ids # => [1,2]
@article.title # => 'hello'
@article.save

or

@article = Article.new({ :category_ids => [1,2], :title => 'hello' })
@article.category_ids # => []
@article.title # => 'hello'

@article = Article.new({ :category_ids => [1,2], :title => 'hello' }, :as => :admin)
@article.category_ids # => [1,2]
@article.title # => 'hello'
@article.save