Does ActiveRecord save a belongs_to association when saving main object?

Question

If I have two models:

class Post < ActiveRecord::Base
  belongs_to :user
end

and

class User < ActiveRecord::Base
  has_many :posts
end

If I do:

post = Post.new
user = User.new
post.user = user
post.save

Does the user get saved as well and the primary key properly assigned in post's user_id field?

Answer 1

ActiveRecord belongs_to associations have the ability to be autosaved along with the parent model, but the functionality is off by default. To enable it:

class Post < ActiveRecord::Base
  belongs_to :user, :autosave => true
end

Answer 2

I believe you want:

class User < ActiveRecord::Base
    has_many :posts, :autosave => true
end

In other words, when saving a User record, seek out all records on the other side of the 'posts' association and save them.