How and where to handle the updating process of associated records?

问题

I am using Ruby on Rails 4 and I would like to properly handle the updating and creating process of associated records through the update_attributes method. That is, I have the following:

# Model
class Article < ActiveRecord::Base
  has_many :categories

  accepts_nested_attributes_for :categories
end

# Controller
class ArticlesController < ApplicationController
  def update
    @article = Article.find(params[:id])

    @article.update_attributes(update_params)
    ...
  end

  private

  def update_params
    params.require(:article).permit(:title, ..., :categories_attributes => [:name, ...])
  end
end

# Logger for the update request
Started PATCH "/articles/6"
Processing by ArticlesController#update
  Parameters: {"utf8"=>"✓", "article"=>{"title"=>"Sample title", "categories_attributes"=>{"0"=>{"name"=>"Sample Category 1", "..."=>"..."}, "1"=>{"name"=>"Sample Category 2", "..."=>"..."}, : "..." => {...}}
  ...

The issue is related to the way Rails handles things for updating associated records in the database, in my case when updating categories through the @article object: when data is submitted so to fire the update action and parameters are passed to the update_attributes method (as shown in the logger above) then Rails creates new category records in the database, one for each element present in the hash categories_attributes.

However, my intention is to update existing category records if those exist or create new ones if those do not exist, accordingly to the uniqueness of article_id and name columns in the categories database table, probabily performing a search for data present in these columns in order to check if it is needed to update or create new records. In fact, in the "edit article" view I display a form with input fields for editing categories including fields pre-populated with data related to existing categories and empty fields for categories that can be created "on the fly" by the editor user.

How can I properly handle this behavior? Is it model or controller responsability? Or, maybe, is there a better way to manage categories directly in the "edit article" view?

回答1:

I believe you need to permit the :id attribute for your nested model:

def update_params
  params.require(:article).permit(
    :title,
    ...,
    :categories_attributes => [:id, :name, ...]
  )
end

And if you want to be able to destroy categories with nested parameters, you'll need to add :_destroy as well. The Rails Guides have the full story.

回答2:

You should add categories_attributes as attr_accessible in your Article model. Like:

attr_accessible :categories_attributes

Without this line you are bound to face issues like above, creating new records instead of updating existing ones. Also there is a gem called nested_form which does an excellent job in building these complex forms.

来源：https://stackoverflow.com/questions/20268557/how-and-where-to-handle-the-updating-process-of-associated-records