Automatically set child.parent_id when parent.children<< child?

How to do that with ActiveRecord? My code:

开发者_运维百科p = Product.create
l = Label.create
p.labels.add << l

But I get l.parent == nil

  create_table "labels", :force => true do |t|
    t.integer  "product_id"
  end

---

Some code from you would be appropriate, since what you're asking should be working automatically.

class Parent < ActiveRecord::Base
  has_many :children
end

class Child < ActiveRecord::Base
  belongs_to :parent
end

If your code doesn't resemble that, then please post a more specific question.

Edit: Does your Product model have any validations in it? They aren't going to pass your code above, and you aren't checking the return value from create, so you'll never know.

---

You could use acts_as_tree for this: http://github.com/rails/acts_as_tree