Can't get Rails :autosave option to work on models

This may be something totally simple, but I can't for the life of me get this working. For some reason, :autosave isn't actually autosaving underlying models.

Here is my schema:

    create_table :albums do |t| 
  t.string :title
  t.text :review

  t.timestamps
end 

create_table :songs do |t| 
  t.integer :album_id
  t.string :name
  t.integer :length
end 

create_table :cover_arts do |t| 
  t.integer :album_id
  t.integer :artist
end 

Here are my models:

class Album < ActiveRecord::Base
  has_ma开发者_StackOverflow社区ny :songs, :autosave => true
  has_one :cover_art, :autosave => true
end

class CoverArt < ActiveRecord::Base
  belongs_to :album
end

class Song < ActiveRecord::Base
  belongs_to :album
end

When I do the following in IRB for an album with cover art that is already in the database:

a = Album.find(1)
a.title = "New title"
a.cover_art.artist = "New Artist"
a.save

It updates the album record but not the CoverArt record. What am I doing wrong?

When this happened to me, I found the betternestedset plugin was overwriting the update method without using alias_method_chain or anything else to maintain the existing call chain. I replaced betternestedset's update rewrite and put a simple attr_readonly call in its place (similar to the existing attr_protected call in that plugin). Perhaps this will help someone somewhere.

According to the docs, you have to save the parent record, not just set a new value, for the child records to also save.

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"