Active Record Autosave Association

AutosaveAssociation is a module that takes care of automatically saving associated records when their parent is saved. In addition to saving, it also destroys any associated records that were marked for destruction. (See mark_for_destruction and marked_for_destruction?).

Saving of the parent, its associations, and the destruction of marked associations, all happen inside a transaction. This should never leave the database in an inconsistent state.

If validations for any of the associations fail, their error messages will be applied to the parent.

Note that it also means that associations marked for destruction won’t be destroyed directly. They will however still be marked for destruction.

Note that :autosave => false is not same as not declaring :autosave. When the :autosave option is not present new associations are saved.

One-to-one Example

class Post
  has_one :author, :autosave => true
end

Saving changes to the parent and its associated model can now be performed automatically and atomically:

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"

Destroying an associated model, as part of the parent’s save action, is as simple as marking it for destruction:

post.author.mark_for_destruction
post.author.marked_for_destruction? # => true

Note that the model is not yet removed from the database:

id = post.author.id
Author.find_by_id(id).nil? # => false

post.save
post.reload.author # => nil

Now it is removed from the database:

Author.find_by_id(id).nil? # => true

One-to-many Example

When :autosave is not declared new children are saved when their parent is saved:

class Post
  has_many :comments # :autosave option is no 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

When :autosave is true all children is saved, no matter whether they are new records:

class Post
  has_many :comments, :autosave => true
end

post = Post.create(:title => 'ruby rocks')
post.comments.create(:body => 'hello world')
post.comments[0].body = 'hi everyone'
post.save # => saves both post and comment, with 'hi everyone' as body

Destroying one of the associated models as part of the parent’s save action is as simple as marking it for destruction:

post.comments.last.mark_for_destruction
post.comments.last.marked_for_destruction? # => true
post.comments.length # => 2

Note that the model is not yet removed from the database:

id = post.comments.last.id
Comment.find_by_id(id).nil? # => false

post.save
post.reload.comments.length # => 1

Now it is removed from the database:

Comment.find_by_id(id).nil? # => true

Validation

Children records are validated unless :validate is false.

activerecord/lib/active_record/autosave_association.rb