Rails tip - "Use model association"

So, I've read in some book about tip "Use model association", which encourages developers to use build methods instead of putting ids via setters.

Assume you have multiple has_many relationships in your model. What's best practise for creating model then ?

For example, let's say you have models Article, User and Group.

class Article < ActiveRecord::Base
  belongs_to :user
  belongs_to :subdomain
end

class User &开发者_开发技巧lt; ActiveRecord::Base
  has_many :articles
end

class Subdomain < ActiveRecord::Base
  has_many :articles
end

and ArticlesController:

class ArticlesController < ApplicationController
  def create
    # let's say we have methods current_user which returns current user and current_subdomain which gets current subdomain
    # so, what I need here is a way to set subdomain_id to current_subdomain.id and user_id to current_user.id
    @article = current_user.articles.build(params[:article])
    @article.subdomain_id = current_subdomain.id
    # or Dogbert's suggestion
    @article.subdomain = current_subdomain
    @article.save
  end
end

Is there a cleaner way ?

Thanks!

---

This should be a little cleaner.

@article.subdomain = current_subdomain

---

The only thing I can think of is merging the subdomain with params:

@article = current_user.articles.build(params[:article].merge(:subdomain => current_subdomain))