Why use "accepts_nested_attributes_for" when you can already save through the parent?

When should I use "accepts_nested_attributes_for"? In the example below, I can d开发者_运维问答o a successful "user.microposts.create" without needing "accepts_nested_attributes_for" in the User model.

class Micropost < ActiveRecord::Base
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :microposts
end

accepts_nested_attributes_for is just a shortcut. It defines a dynamic attribute {field_name}_attributes so that if you have a form you can include nested attributes and have it automatically assign them to an association. Like so :

form_for :object do |f|
  f.text_field :attr1
  f.text_field :attr2
  f.fields_for :association_attributes do |g|
    g.text_field :nested1
    g.text_field :nested2
  end
end

This posts with parameters {object: {attr1: val, attr2: val, association_attributes: {nested1: val, nested2: val}} and adding accepts_nested_attributes_for :association to your class makes the whole thing work without any extra code.