Question

Given the following controller code

def update
  params[:image][:contributor_ids] ||= []
  params[:image][:category_ids] ||= []
  @image = Image.find( params[:id] )
  if @image.update_attributes params[:image]
    redirect_to session[:return_to]
  else
    render :edit
  end
end

And the following image model

class Image < ActiveRecord::Base

  has_many :category_links, :as => :categorizable, :dependent => :destroy
  has_many :categories, :through => :category_links

  has_many :contributions, :as => :contributable, :dependent => :destroy
  has_many :contributors, :through => :contributions
  # .... omitted for clarity
end

When the update_attributes gets called with just the associations being changed
ActiveRecord does not change the updated_at column – why is that and how to change that behavior ?

Answer 1

I think this is happening because when you have a N:N relation and you update that relation, you are actually creating/modifying/deleting records in the join table (in this case, contributions or category_links), and not actually updating the @image instance itself.