Problem with an Tree-like object hierarchy (ActiveRecord act

Hello people on rails,

I am developing a web interface for a database that has hierarchical
data. I want the user to be able to browse the tree (~1300 nodes) and
activate/deactivate and showing/hiding groups of nodes (like
selecting one node selects all the children and the leafs). So I have
a tree of objects (ActiveRecord acts_as_tree). Because I need the
tree to be persistent and I don’t want to resend the whole thing
after every change I use Ajax to update only the parts that changed.
This all works like a charm! Sending a message (eg activation) down
the tree (root->leafs) is fine.
Now the problem: when I pick an node from the tree and try to
activate itself and all its ancestors, only the one element will get
activated. Trying something like my_node.children[0] =
true doesn’t work either. When I make the call recursive like

def show_up
puts “activating #{}”
@active = true
if parent then parent.show_up end

I can see in the log file that its traversing all the way up to the
root, but only the activation of the node called will ‘stick’.
speaking of ‘stick’, to preserve the tree between requests I store it
in the session variable and retrieve it from there:

def unfreeze_taxtree
if taxtree_frozen then return Marshal.load(session[:tax_tree])
else return nil end

def freeze_taxtree(tax)
return session[:tax_tree] = Marshal.dump(tax)

def get_tax_from_freezer(tax_id)
@@tax_tree = unfreeze_taxtree

So tax are the nodes and tax_tree the … well … tree.
I did the marshaling and retrieving via object id because I was
getting paranoid about the objects not being the original ones after
unfreezing from the session cache.
Before the first freezing I tried to send down a ping from the root
to all the twigs and back, to force the instantiation of all children
and parents. No cure.
I thinks it boils down to: what is the difference between children
and parents?

I would greatly appreciate any thoughts or help on this.

cheers, Florian

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