Added ability to touch the parent

[seuros]

Just add :touch => true to the options of acts_as_tree.

[mceachen]

I don't quite understand this request—are you wanting children to force an update on parents? Why?

It looks like this pull request adds the option, but no implementation. If you want to add an implementation with test coverage, I'm happy to take a new PR.

Thanks!

[seuros]

I'm using closure for nested menus. When a child is updated, the root item need to be touched to invalidate the cache.

[mceachen]

Do you want to make the touch be recursive, or should it only touch the immediate parent?

[seuros]

in my case, i need to invalidated the root.
Active-record has the recursive touching implemented.
But i think we could improve the recursive touching by just 2 queries with closure_tree: (Get the ancestor_ids, touch them at once by updating the updated_at)

[seuros]

I will send another PR when i write tests

[mgwidmann]

Caching is broken without this feature... sad, have to implement your own touch functionality. 👎

[seuros]

I reimplemented it in another commit. just add touch: true to the ct options

[mgwidmann]

Well then this feature is broken. Using version 5.2.0 the following code does not work as expected:
(Below I've changed the model and ids, but I did run this code in my app)

child = MyTree.find(123)
parent = Mytree.find(456)
parent.children     # #<ActiveRecord::Associations::CollectionProxy []>
child.parent          # nil
child.update(parent_id: parent.id)
child.updated_at       # Mon, 15 Jun 2015 11:13:38 EDT -04:00
parent.updated_at    # Mon, 15 Jun 2015 10:52:53 EDT -04:00

The two updated_at timestamps should be identical (if not a small fraction of time different). The above shows the parent hasn't been touched in the last 20 minutes, meaning my cache was not busted.

[mgwidmann]

As the documentation in the README says:

:touch delegates to the belongs_to annotation for the parent, so touching cascades to all children (the performance of this for deep trees isn't currently optimal).

It does not touch parents (touching cascades to all children).

[mgwidmann]

My workaround:

before_save do
    if parent_id_changed?
      self.class.where(id: [parent_id, parent_id_was].compact).update_all(updated_at: Time.now)
    end
  end

Successfully busts the cache when child.update(parent_id: new_parent.id) is called, busting both old parent and new parent. Does not do recursive busting.