rails associations :autosave doesn't seem to working as expected

Question

I made a real basic github project here that demonstrates the issue. Basically, when I create a new comment, it is saved as expected; when I update an existing comment, it isn't saved. However, that isn't what the docs for :autosave => true say ... they say the opposite. Here's the code:

class Post < ActiveRecord::Base
  has_many :comments, 
           :autosave => true, 
           :inverse_of => :post,
           :dependent => :destroy

  def comment=(val)
    obj=comments.find_or_initialize_by(:posted_at=>Date.today)
    obj.text=val
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post, :inverse_of=>:comments
end

Now in the console, I test:

p=Post.create(:name=>'How to groom your unicorn')
p.comment="That's cool!"
p.save!
p.comments # returns value as expected. Now we try the update case ... 

p.comment="But how to you polish the rainbow?"
p.save!
p.comments # oops ... it wasn't updated

Why not? What am I missing?

Note if you don't use "find_or_initialize", it works as ActiveRecord respects the association cache - otherwise it reloads the comments too often, throwing out the change. ie, this implementation works

def comment=(val)
  obj=comments.detect {|obj| obj.posted_at==Date.today}
  obj = comments.build(:posted_at=>Date.today) if(obj.nil?)
  obj.text=val
end

But of course, I don't want to walk through the collection in memory if I could just do it with the database. Plus, it seems inconsistent that it works with new object but not an existing object.

Answer 1

Here is another option. You can explicitly add the record returned by find_or_initialize_by to the collection if it is not a new record.

def comment=(val)
  obj=comments.find_or_initialize_by(:posted_at=>Date.today)
  unless obj.new_record?
    association(:comments).add_to_target(obj) 
  end
  obj.text=val
end