Railsのhas_oneのsaveに注意！

has_one(1:1)のアソシエーションの場合

autosave: trueを付けないと、アソシエーション先authorのnameを変更してpostをsaveしても、authorはsaveされない

class Post
  has_one :author, autosave: true
end

post = Post.find(1)
post.title       # => "The current global position of migrating ducks"
post.author.name # => "alloy"

post.title = "On the migration of ducks"
post.author.name = "Eloy Duran"

post.save
post.reload
post.title       # => "On the migration of ducks"
post.author.name # => "Eloy Duran”

has_many(1:N)のリレーションの場合

• autosaveオプションは、不要
• postをsaveすると、commentsもsaveされる

class Post
  has_many :comments # :autosave option is not declared
end

post = Post.new(title: 'ruby rocks')
post.comments.build(body: 'hello world')
post.save # => saves both post and comment

post = Post.create(title: 'ruby rocks')
post.comments.build(body: 'hello world')
post.save # => saves both post and comment

post = Post.create(title: 'ruby rocks')
post.comments.create(body: 'hello world')
post.save # => saves both post and comment

ActiveRecord::AutosaveAssociation