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 then new association records are saved but the updated association records are not saved.

Validation

Child records are validated unless :validate is false.

Callbacks

Association with autosave option defines several callbacks on your model (around_save, before_save, after_create, after_update). Please note that callbacks are executed in the order they were defined in model. You should avoid modifying the association content before autosave callbacks are executed. Placing your callbacks after associations is usually a good practice.

One-to-one Example

class Post < ActiveRecord::Base
  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 < ActiveRecord::Base
  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')
comment = post.comments.create(body: 'hello world')
comment.body = 'hi everyone'
post.save # => saves post, but not comment

When :autosave is true all children are saved, no matter whether they are new records or not:

class Post < ActiveRecord::Base
  has_many :comments, autosave: true
end

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

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

post.comments # => [#<Comment id: 1, ...>, #<Comment id: 2, ...]>
post.comments[1].mark_for_destruction
post.comments[1].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

Caveats

Note that autosave will only trigger for already-persisted association records if the records themselves have been changed. This is to protect against SystemStackError caused by circular association validations. The one exception is if a custom validation context is used, in which case the validations will always fire on the associated records.

activerecord/lib/active_record/autosave_association.rb